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In article , Uwe
writes: 12V, holy cow! If I go low voltage I keep it at around 5. I am building a controller board with basic stamps and recently fried an A/D chip by letting it have 12V, it was lethal. Heh heh heh...you low-voltage kids are all alike. Us vacuum veterans would not think twice about the +120 VDC (the "B+") in the old "All-American Five" cheap table model AM BC radios.... :-) By the way, talking about overload. The issue of crystals breaking has been mentioned a few times, but how do I measure what the crystal "sees" for current and what is tooo much??? Seriously, folks, the websites for International Crystal, Corning Frequency Control division, etc., all give specs on various sizes and cuts of their quartz crystal units. Few really "measure" the crystal drive levels since that can be done analytically...if one knows how to do this. If not, there are several hints on the various crystal unit websites for approximating that, such as typical circuits. The best approach at the beginning is to take advice from others on what works and what doesn't...such as the old, old FT-243 holder crystals can take more power dissipation (thicker slice of quartz) than most of the smaller HC-6 holder units. The newer SMD quartz crystal units have very low power specs and should not be used with most vacuum tube circuits because of that. Having been in the electron-pushing racket for better than a half century and bridging the tube and transistor eras, I've never experienced any quartz crystal physically "breaking." If a quartz crystal circuit stopped working, the quartz unit just sat there without a sound, same as it did when it worked OK. :-) Only the oscilloscope trace knew what was in the hearts of such circuits... Len Anderson retired (from regular hours) electronic engineer person |
By the way, talking about overload. The issue of crystals breaking has been mentioned a few times, but how do I measure what the crystal "sees" for current and what is tooo much??? It's not easy to measure crystal current, since it's RF current at the crystals frequency of oscillation. Most AC milliameters will stop working at about 10Khz, and the lead length and impedance will probably throw off your oscillator. One "trick" we used in the old days, which also sometimes saved the crystal from destruction, was to put a low current pilot lamp in series with the crystal. Seems to me it was a #49, but you'd best look it up. My recollection was that this was a 60ma bulb. In normal operation it should not glow visibly. Doug Moore KB9TMY |
By the way, talking about overload. The issue of crystals breaking has been mentioned a few times, but how do I measure what the crystal "sees" for current and what is tooo much??? It's not easy to measure crystal current, since it's RF current at the crystals frequency of oscillation. Most AC milliameters will stop working at about 10Khz, and the lead length and impedance will probably throw off your oscillator. One "trick" we used in the old days, which also sometimes saved the crystal from destruction, was to put a low current pilot lamp in series with the crystal. Seems to me it was a #49, but you'd best look it up. My recollection was that this was a 60ma bulb. In normal operation it should not glow visibly. Doug Moore KB9TMY |
In article ,
"Paul_Morphy" writes: " Uncle Peter" wrote in message news:vQnbc.9210$pM1.6556@lakeread06... I suggest he put all his radios on a shelf, and get a cell phone. No dangerous RF levels, no deadly voltages... NOT Gee, Unc, have a tough week? : I don't want him to give up radio, I just don't think an Ameco AC-1 is worth the trouble. But he does think it's worth the trouble. I didn't want one when I was 15 and they were new, and I wouldn't waste my time fiddling with one now. Nobody is saying *you* should. But your're saying Uwwe shouldn't. See the contradiction? 73 de Jim, N2EY |
In article ,
"Paul_Morphy" writes: " Uncle Peter" wrote in message news:vQnbc.9210$pM1.6556@lakeread06... I suggest he put all his radios on a shelf, and get a cell phone. No dangerous RF levels, no deadly voltages... NOT Gee, Unc, have a tough week? : I don't want him to give up radio, I just don't think an Ameco AC-1 is worth the trouble. But he does think it's worth the trouble. I didn't want one when I was 15 and they were new, and I wouldn't waste my time fiddling with one now. Nobody is saying *you* should. But your're saying Uwwe shouldn't. See the contradiction? 73 de Jim, N2EY |
In article , Uwe
writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Nobody has complained yet anyways and maybe the chirp is worse in my receiver than on the air, as someone here suggested. By the way I use a Icom R75 for a receiver and switch the antenna off during transmit-still plenty of a signal seems to get into the receiver anyways. It is quite possible that the receiver is being overloaded by the large signal and creating a chirp. 73 de Jim, N2EY |
In article , Uwe
writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Nobody has complained yet anyways and maybe the chirp is worse in my receiver than on the air, as someone here suggested. By the way I use a Icom R75 for a receiver and switch the antenna off during transmit-still plenty of a signal seems to get into the receiver anyways. It is quite possible that the receiver is being overloaded by the large signal and creating a chirp. 73 de Jim, N2EY |
in article , N2EY at
PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. The coil which works best with my tx is 8 turns on a 1,125" ceramic core. To get guess work out of it I just bought and built a L/C meter and measured my coil to have 2.7 microhenry. So I am way off, but it works, sort of. The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so that seem right. All this happens with B+200V and 35 mA plate current. Older ARRL handbooks give typical values for pi network for 50 Ohm antenna loads and my values are in range for the caps but my coil is too small. The ouput voltage on my antenna measured with a scope is up to 75 volts peak to peak, with a 50 Ohm load that would mean I get more out of the tx than I put into it and I am not of the sort who says this might happen. So my conclusion is, and tell me if this sounds right, that I have an antenna which is far from 50 ohm resistive at 40m and that that makes everything weird. The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. 73 Uwe |
"Uwe" wrote in message ... The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The pi network should be able to match a wide range of impedances but it would help to connect a known resistive load. Five, 2-watt, 270-ohm resistors in parallel would be close enough. If you're getting a dip in plate current the circuit is resonating somewhere, and you say you've worked people, so it's putting some rf on the band. See if you're getting two dips. A lot of those pi networks would resonate on the operating band with the plate tuning cap almost completely meshed, but there was enough range in the cap that it would also tune to the second harmonic. If your LC meter is right you may be dipping at a harmonic, not the fundamental. OTOH, if your calculation of what the original coil was is correct, the plate tuning capacitor should resonate when its value is about 20 pF -- for a 22-uH coil. That doesn't mesh with the range of your plate tuning cap. A 2.7 uH coil would resonate with the plate tuning cap at about 185 pF, which seems more reasonable. This is one of those rare occasions when a grid-dip meter is handy. Is there a ham club in your area? Someone may have one to lend. Meanwhile, hook it up to a dummy load and see what you get. There's something else you could try, but I don't know how well it would work. With the AC-1 unplugged you could connect your receiver antenna to the top of the plate tuning cap and adjust the plate tuning cap while listening for a peak in the noise level. That would tell you the circuit was resonating at 7 MHz. If NG, try 20 meters and 10 meters. In the olden days I had a 6BE6 connected inside my Viking Valiant, such that it turned on and bridged the receiver antenna input when transmitted rf appeared at the grid. When the key was up, rf from the antenna passed into the receiver. This allowed for full break-in CW, and I could dip the plate tuning cap just by listening to the noise level. Real handy when moving around the band in a contest. You would probably pop the front end of a solid-state receiver doing this, so don't try it. The circuit was in an old Radio Handbook, which was edited by Bill Orr, W6SAI. That's what made me think that you could try this with your receiver, but exercise appropriate caution. You know, I think you can get coil forms to fit your rig from Antique Radio Supply, and also maybe Ocean State Electronics (oselectronics.com). You could even make one for 30 meters. Ocean State has a power transformer in their catalog that may do for a power supply for your rig, too. Or look for an old tube-type hi-fi receiver in a thrift shop or at a tag sale. If you're going to do, you may as well do it! : 73, "PM" |
"Uwe" wrote in message ... The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The pi network should be able to match a wide range of impedances but it would help to connect a known resistive load. Five, 2-watt, 270-ohm resistors in parallel would be close enough. If you're getting a dip in plate current the circuit is resonating somewhere, and you say you've worked people, so it's putting some rf on the band. See if you're getting two dips. A lot of those pi networks would resonate on the operating band with the plate tuning cap almost completely meshed, but there was enough range in the cap that it would also tune to the second harmonic. If your LC meter is right you may be dipping at a harmonic, not the fundamental. OTOH, if your calculation of what the original coil was is correct, the plate tuning capacitor should resonate when its value is about 20 pF -- for a 22-uH coil. That doesn't mesh with the range of your plate tuning cap. A 2.7 uH coil would resonate with the plate tuning cap at about 185 pF, which seems more reasonable. This is one of those rare occasions when a grid-dip meter is handy. Is there a ham club in your area? Someone may have one to lend. Meanwhile, hook it up to a dummy load and see what you get. There's something else you could try, but I don't know how well it would work. With the AC-1 unplugged you could connect your receiver antenna to the top of the plate tuning cap and adjust the plate tuning cap while listening for a peak in the noise level. That would tell you the circuit was resonating at 7 MHz. If NG, try 20 meters and 10 meters. In the olden days I had a 6BE6 connected inside my Viking Valiant, such that it turned on and bridged the receiver antenna input when transmitted rf appeared at the grid. When the key was up, rf from the antenna passed into the receiver. This allowed for full break-in CW, and I could dip the plate tuning cap just by listening to the noise level. Real handy when moving around the band in a contest. You would probably pop the front end of a solid-state receiver doing this, so don't try it. The circuit was in an old Radio Handbook, which was edited by Bill Orr, W6SAI. That's what made me think that you could try this with your receiver, but exercise appropriate caution. You know, I think you can get coil forms to fit your rig from Antique Radio Supply, and also maybe Ocean State Electronics (oselectronics.com). You could even make one for 30 meters. Ocean State has a power transformer in their catalog that may do for a power supply for your rig, too. Or look for an old tube-type hi-fi receiver in a thrift shop or at a tag sale. If you're going to do, you may as well do it! : 73, "PM" |
Uwe wrote in message ...
in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns The coil which works best with my tx is 8 turns on a 1,125" ceramic core. But do you get a dip? Be aware that the AC-1 went through some changes in its lifetime. Some models used a filter choke, others did not. Some used a 730 uuf loading capacitor, others just a single-section 365 uuf one. Coils changed too. To get guess work out of it I just bought and built a L/C meter and measured my coil to have 2.7 microhenry. So I am way off, but it works, sort of. The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so that seem right. All this happens with B+200V and 35 mA plate current. LC = 25,330/(f * f) so for 7 MHz, the LC constant is 516. Your 2.7 uH coil should resonate with 191 uuf. Older ARRL handbooks give typical values for pi network for 50 Ohm antenna loads and my values are in range for the caps but my coil is too small. The ouput voltage on my antenna measured with a scope is up to 75 volts peak to peak, with a 50 Ohm load that would mean I get more out of the tx than I put into it and I am not of the sort who says this might happen. So my conclusion is, and tell me if this sounds right, that I have an antenna which is far from 50 ohm resistive at 40m and that that makes everything weird. That's defintitely part of the problem. What antenna are you using? Have you tried a resistor or lamp load? The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The meter tells more. You can use a pilot light (#47, 150 mA) instead of a meter. Sudden thought: Where is the meter connected? Are you reading plate current, or plate-and-screen current combined? Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
Uwe wrote in message ...
in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns The coil which works best with my tx is 8 turns on a 1,125" ceramic core. But do you get a dip? Be aware that the AC-1 went through some changes in its lifetime. Some models used a filter choke, others did not. Some used a 730 uuf loading capacitor, others just a single-section 365 uuf one. Coils changed too. To get guess work out of it I just bought and built a L/C meter and measured my coil to have 2.7 microhenry. So I am way off, but it works, sort of. The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so that seem right. All this happens with B+200V and 35 mA plate current. LC = 25,330/(f * f) so for 7 MHz, the LC constant is 516. Your 2.7 uH coil should resonate with 191 uuf. Older ARRL handbooks give typical values for pi network for 50 Ohm antenna loads and my values are in range for the caps but my coil is too small. The ouput voltage on my antenna measured with a scope is up to 75 volts peak to peak, with a 50 Ohm load that would mean I get more out of the tx than I put into it and I am not of the sort who says this might happen. So my conclusion is, and tell me if this sounds right, that I have an antenna which is far from 50 ohm resistive at 40m and that that makes everything weird. That's defintitely part of the problem. What antenna are you using? Have you tried a resistor or lamp load? The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The meter tells more. You can use a pilot light (#47, 150 mA) instead of a meter. Sudden thought: Where is the meter connected? Are you reading plate current, or plate-and-screen current combined? Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
"N2EY" wrote in message om... This is just a temporary setup to see if the RFC is OK. My recollection is hazy but I seem to recall that when the loading cap was open too far for the load the pi net was seeing, the dip got very shallow. I'll bet his antenna is outside the range it can match. Time for Uwe to gather up some of that coil-winding stuff and make a tuner. 73, "PM" |
"N2EY" wrote in message om... This is just a temporary setup to see if the RFC is OK. My recollection is hazy but I seem to recall that when the loading cap was open too far for the load the pi net was seeing, the dip got very shallow. I'll bet his antenna is outside the range it can match. Time for Uwe to gather up some of that coil-winding stuff and make a tuner. 73, "PM" |
in article , N2EY at
wrote on 4/6/04 12:29: Uwe wrote in message ... in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns Well, the way I use the formula is 1.25*1.25*15*15/((9*1.25)+(10*0.45)) = 351.5/15.75 = 22.3 O.45 is the length of the 15 windings. Do I not use the formula properly?? My meter is built into my bench power supply (thats why it reads up to 250mA), so I am measuring plate and screen current. I put in a second meter which would only measure the plate current but its reading is practicly identical to the first one, as if there was no grid current. My antenna is a dipole of about 75ft. length each side, connected with a 50 ohm coax, no balun or such things. I will need a few days to try out some of the things you and also Paul suggested and it might really be a good idea to get an SWR meter and a tuner. All in due time and I will surely get back to you. Thanks for the help Uwe The coil which works best with my tx is 8 turns on a 1,125" ceramic core. But do you get a dip? Be aware that the AC-1 went through some changes in its lifetime. Some models used a filter choke, others did not. Some used a 730 uuf loading capacitor, others just a single-section 365 uuf one. Coils changed too. To get guess work out of it I just bought and built a L/C meter and measured my coil to have 2.7 microhenry. So I am way off, but it works, sort of. The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so that seem right. All this happens with B+200V and 35 mA plate current. LC = 25,330/(f * f) so for 7 MHz, the LC constant is 516. Your 2.7 uH coil should resonate with 191 uuf. Older ARRL handbooks give typical values for pi network for 50 Ohm antenna loads and my values are in range for the caps but my coil is too small. The ouput voltage on my antenna measured with a scope is up to 75 volts peak to peak, with a 50 Ohm load that would mean I get more out of the tx than I put into it and I am not of the sort who says this might happen. So my conclusion is, and tell me if this sounds right, that I have an antenna which is far from 50 ohm resistive at 40m and that that makes everything weird. That's defintitely part of the problem. What antenna are you using? Have you tried a resistor or lamp load? The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The meter tells more. You can use a pilot light (#47, 150 mA) instead of a meter. Sudden thought: Where is the meter connected? Are you reading plate current, or plate-and-screen current combined? Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
in article , N2EY at
wrote on 4/6/04 12:29: Uwe wrote in message ... in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns Well, the way I use the formula is 1.25*1.25*15*15/((9*1.25)+(10*0.45)) = 351.5/15.75 = 22.3 O.45 is the length of the 15 windings. Do I not use the formula properly?? My meter is built into my bench power supply (thats why it reads up to 250mA), so I am measuring plate and screen current. I put in a second meter which would only measure the plate current but its reading is practicly identical to the first one, as if there was no grid current. My antenna is a dipole of about 75ft. length each side, connected with a 50 ohm coax, no balun or such things. I will need a few days to try out some of the things you and also Paul suggested and it might really be a good idea to get an SWR meter and a tuner. All in due time and I will surely get back to you. Thanks for the help Uwe The coil which works best with my tx is 8 turns on a 1,125" ceramic core. But do you get a dip? Be aware that the AC-1 went through some changes in its lifetime. Some models used a filter choke, others did not. Some used a 730 uuf loading capacitor, others just a single-section 365 uuf one. Coils changed too. To get guess work out of it I just bought and built a L/C meter and measured my coil to have 2.7 microhenry. So I am way off, but it works, sort of. The air caps are 36 to 420pf at the plate and 15 to 728pf at the antenna, so that seem right. All this happens with B+200V and 35 mA plate current. LC = 25,330/(f * f) so for 7 MHz, the LC constant is 516. Your 2.7 uH coil should resonate with 191 uuf. Older ARRL handbooks give typical values for pi network for 50 Ohm antenna loads and my values are in range for the caps but my coil is too small. The ouput voltage on my antenna measured with a scope is up to 75 volts peak to peak, with a 50 Ohm load that would mean I get more out of the tx than I put into it and I am not of the sort who says this might happen. So my conclusion is, and tell me if this sounds right, that I have an antenna which is far from 50 ohm resistive at 40m and that that makes everything weird. That's defintitely part of the problem. What antenna are you using? Have you tried a resistor or lamp load? The dips in plate current are nearly imperceptible and they are not aided by my 250mA full scale meter. They may be 2 or 3 mA. I tune with the help of my scope. The meter tells more. You can use a pilot light (#47, 150 mA) instead of a meter. Sudden thought: Where is the meter connected? Are you reading plate current, or plate-and-screen current combined? Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
In article , Uwe
writes: in article , N2EY at wrote on 4/6/04 12:29: Uwe wrote in message ... in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns Well, the way I use the formula is 1.25*1.25*15*15/((9*1.25)+(10*0.45)) = 351.5/15.75 = 22.3 O.45 is the length of the 15 windings. Do I not use the formula properly?? You used the coil *diameter* where you should have used the coil *radius*. A coil with diameter of 1.25 inch has a radius of 0.625 inch. Compute 0.625*0.625*15*15/((9*0.625)+(10*0.45)) = and see what you get. My meter is built into my bench power supply (thats why it reads up to 250mA), so I am measuring plate and screen current. I put in a second meter which would only measure the plate current but its reading is practicly identical to the first one, as if there was no grid current. That's odd. My antenna is a dipole of about 75ft. length each side, connected with a 50 ohm coax, no balun or such things. 150 feet total length? That's not resonant on 40 meters, and your SWR with 50 ohm coax is probably quite high. A half-wave 40 meter dipole is about 66-67 feet long (33 feet each side), and will have a fairly low SWR on 40 meters when fed with 50 ohm coax. The next length that will give a fairly low 40 meter SWR is about 205 feet overall (102 feet each side). Such a dipole is one-and-a-half waves long. These are "ballpark" figures, not exact ones. How high is your dipole? I agree with Paul Morphy that a simple dummy load is best for testing. His suggestion of paralleled noninductive resistors is excellent. I will need a few days to try out some of the things you and also Paul suggested and it might really be a good idea to get an SWR meter and a tuner. That will work, but first get the rig working correctly into a dummy load. All in due time and I will surely get back to you. If it takes me a while to respond, it's because I'm away from the computer. Thanks for the help You're welcome. 73 de Jim, N2EY |
In article , Uwe
writes: in article , N2EY at wrote on 4/6/04 12:29: Uwe wrote in message ... in article , N2EY at PAMNO wrote on 4/5/04 18:59: In article , Uwe writes: I will just have to fiddle a bit more with the pi network (since at the B+ voltages suggested here my plate current would be way high) and I will have to live with the chirp. Are you getting a "dip" in plate current? If not, the coil is probably too large or too small. Unless you get a real dip, the output network isn;t right. I have used a very similar transmitter with 350 volts on the plate, and the dip is clean and pronounced. Jim, the original docs I got for this tx call, at 40 m, for a 15 turn coil on the coil form provided with the kit, which I hear was 1.25" diameter. If I use the formula for air coils this turns out to be roughly a 22 microhenry coil. 22 microhenries? I get more like 8 microhenries using the formula L = (a * a * n * n)/([9 * a] + [10 * b]) where a = radius of coil in inches b = length of winding in inches n = number of turns Well, the way I use the formula is 1.25*1.25*15*15/((9*1.25)+(10*0.45)) = 351.5/15.75 = 22.3 O.45 is the length of the 15 windings. Do I not use the formula properly?? You used the coil *diameter* where you should have used the coil *radius*. A coil with diameter of 1.25 inch has a radius of 0.625 inch. Compute 0.625*0.625*15*15/((9*0.625)+(10*0.45)) = and see what you get. My meter is built into my bench power supply (thats why it reads up to 250mA), so I am measuring plate and screen current. I put in a second meter which would only measure the plate current but its reading is practicly identical to the first one, as if there was no grid current. That's odd. My antenna is a dipole of about 75ft. length each side, connected with a 50 ohm coax, no balun or such things. 150 feet total length? That's not resonant on 40 meters, and your SWR with 50 ohm coax is probably quite high. A half-wave 40 meter dipole is about 66-67 feet long (33 feet each side), and will have a fairly low SWR on 40 meters when fed with 50 ohm coax. The next length that will give a fairly low 40 meter SWR is about 205 feet overall (102 feet each side). Such a dipole is one-and-a-half waves long. These are "ballpark" figures, not exact ones. How high is your dipole? I agree with Paul Morphy that a simple dummy load is best for testing. His suggestion of paralleled noninductive resistors is excellent. I will need a few days to try out some of the things you and also Paul suggested and it might really be a good idea to get an SWR meter and a tuner. That will work, but first get the rig working correctly into a dummy load. All in due time and I will surely get back to you. If it takes me a while to respond, it's because I'm away from the computer. Thanks for the help You're welcome. 73 de Jim, N2EY |
Jim, after my calculation of the coil were wrong I thought it was about time
to check everything and I did and to try and distinguish between radius and diameter... Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. Happy about the dip but still not clear on the deeper reasons... 73 Uwe Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
Jim, after my calculation of the coil were wrong I thought it was about time
to check everything and I did and to try and distinguish between radius and diameter... Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. Happy about the dip but still not clear on the deeper reasons... 73 Uwe Here's something else to try: Often trouble of this sort is due to the RF choke used. What RFCs are you suing, particularly in the plate circuit? Although the LC meter may say they are a certain L, in real life they may have all sorts of unwanted resonances. To test this idea out, do the following: - Remove the plate RFC - Connect the antenna end of the plate coil to the B+ where the RFC used to be connected. This point should already be bypassed to ground through a disk capacitor of about .01 uF - Disconnect the "loading" capacitor - Remove the plate coupling capacitor. What you will then have is the 200 volts being fed to the plate through the coil, with one end of the coil going to the plate supply and the other end connected directly to the plate of the 6V6. The plate tuning capacitor is connected between the plate of the 6V6 and ground. End result is no plate RFC and a parallel resonant circuit. There's no connection for an antenna yet, but that's not important right now. Test out the rig and look for the plate current dip. It should be very obvious because there is no load connected. This is just a temporary setup to see if the RFC is OK. 73 es GL de Jim, N2EY |
In article , Uwe
writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY |
In article , Uwe
writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY |
in article , N2EY at
PAMNO wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe |
in article , N2EY at
PAMNO wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe |
In article , Uwe
writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY |
In article , Uwe
writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY |
in article , N2EY at
PAMNO wrote on 4/9/04 19:59: In article , Uwe writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY Thanks for the good wishes. Yes I got the ticket and I am out there with my 5 wpm but sometimes I really feel I don't belong there, 5 wpm in the "laboratory conditons" of the test is one thing, out there with all that noise and distraction is an altogether different thing and "stagefright" takes over sometimes. (www.oldradioparts.com) seems like a good source, I might buy from them sometimes, I still need a transformer for the little transmitter. By the way about specifying these transformers, to get those 320Volt with a tube rectifier do you need a centertapped transformer with roughly 160V in each winding, what they call a 160-0-160?? I did see these other AC-1 sites and yes I do use the smaller resistor parallel to the crystal. I read a little more about chokes in old radio amateur handbooks and it seems that even their placement in the chassis can be tricky. I would love to know a way, because even with the 'new' choke the rig is not 'there' yet, to possibly make a test setup for this entire pi section and 'bench test it. Is there such a thing? If I terminate it with a 50 load and feed my HF generator signal on the input (plate) side this would not be appropriate because the tx and the test generator have a different output impedance?? And what do you want the pi section to do, resonate at the transmitter frequency? Ways to go... 73 Uwe |
in article , N2EY at
PAMNO wrote on 4/9/04 19:59: In article , Uwe writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY Thanks for the good wishes. Yes I got the ticket and I am out there with my 5 wpm but sometimes I really feel I don't belong there, 5 wpm in the "laboratory conditons" of the test is one thing, out there with all that noise and distraction is an altogether different thing and "stagefright" takes over sometimes. (www.oldradioparts.com) seems like a good source, I might buy from them sometimes, I still need a transformer for the little transmitter. By the way about specifying these transformers, to get those 320Volt with a tube rectifier do you need a centertapped transformer with roughly 160V in each winding, what they call a 160-0-160?? I did see these other AC-1 sites and yes I do use the smaller resistor parallel to the crystal. I read a little more about chokes in old radio amateur handbooks and it seems that even their placement in the chassis can be tricky. I would love to know a way, because even with the 'new' choke the rig is not 'there' yet, to possibly make a test setup for this entire pi section and 'bench test it. Is there such a thing? If I terminate it with a 50 load and feed my HF generator signal on the input (plate) side this would not be appropriate because the tx and the test generator have a different output impedance?? And what do you want the pi section to do, resonate at the transmitter frequency? Ways to go... 73 Uwe |
Uwe wrote in message ...
in article , N2EY at PAMNO wrote on 4/9/04 19:59: In article , Uwe writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY Thanks for the good wishes. Yes I got the ticket and I am out there with my 5 wpm but sometimes I really feel I don't belong there, 5 wpm in the "laboratory conditons" of the test is one thing, out there with all that noise and distraction is an altogether different thing and "stagefright" takes over sometimes. You do belong there, Uwe. You just need to develop skills, that's all. And the only way to get them is on-the-air. (www.oldradioparts.com) seems like a good source, I might buy from them sometimes, I still need a transformer for the little transmitter. By the way about specifying these transformers, to get those 320Volt with a tube rectifier do you need a centertapped transformer with roughly 160V in each winding, what they call a 160-0-160?? No! That will get you far less than what you need. With theoretically "perfect" rectifiers and transformers, the output voltage depends entirely on the type of filter and the transformer voltage. With a full-wave center-tap rectifier and a choke-input filter, the maximum voltage obtainable is 0.9 times the transformer voltage, and with a capacitor input filter, the maximum voltage obtainable is 1.414 times the transformer voltage. With the full-wave center-tap rectifier, "transformer voltage" means "each side of center tap". The above numbers assume perfect components whose ratings are big enough to do the job. With real world components, it's a little more complicated, but the results are always that you get less voltage. The AC-1 uses a capacitor-input filter and a 6X5GT rectifier. Also, the transformer is not "perfect" - just good enough to do the job. End result is that the transformer is about 320-0-320 and the resulting DC is about 325 volts. Easiest way to work with tube rectifiers is to look them up in the tube manuals (there are several tube manuals on-line) and look at the design curves. I did see these other AC-1 sites and yes I do use the smaller resistor parallel to the crystal. Excellent. May take some experimentation. btw, check out AF4K's website for crystal suppliers. I read a little more about chokes in old radio amateur handbooks and it seems that even their placement in the chassis can be tricky. I would love to know a way, because even with the 'new' choke the rig is not 'there' yet, to possibly make a test setup for this entire pi section and 'bench test it. Is there such a thing? Yes, but it's not necessary. You know the capacitors are the right ones, so it's merely a matter of the chokes and coil. If I terminate it with a 50 load and feed my HF generator signal on the input (plate) side this would not be appropriate because the tx and the test generator have a different output impedance?? That's exactly right. And what do you want the pi section to do, resonate at the transmitter frequency? Yes. But more than just resonate, it transforms the load impedance from 50 ohms to whatever the tube needs. Ways to go... Good luck & congrats again! 73 de Jim, N2EY |
Uwe wrote in message ...
in article , N2EY at PAMNO wrote on 4/9/04 19:59: In article , Uwe writes: Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. That should be a good one. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? "Play Things of The Past" (www.oldradioparts.com) is one. Antique Electric Supply (www.tubesandmore.com) is another. JWMiller still makes pie-wound 2.5 millihenry chokes with phenolic (no iron) cores. Check Digi-Key and Mouser. Also google "AC1 ameco" - several websites with more info. One site I visited (whose url I didn't save!) listed the plate voltage as approximately 325 volts. This site also cautioned that the original grid resistor (47 K?) is way too high, and that better results are obtained with a grid resistor of 4.7 K to 15 K. The author says the smaller value grid resistor gives less chirp. The traditional amateur way to measure grid current is with a small lamp in series with the xtal. "Small" means a #48 or #49 bulb - 2 volts at 60 ma. The common #47 lamp needs 6.3 volts at 150 ma. and is way too insensitive. Small flashlight lamps such as used in single-cell penlights may also be useful. But the lamp should only be used for testing. Its resistance may cause chirp. and before I forget: CONGRATS ON YOUR GENERAL, Uwe! 73 de Jim, N2EY Thanks for the good wishes. Yes I got the ticket and I am out there with my 5 wpm but sometimes I really feel I don't belong there, 5 wpm in the "laboratory conditons" of the test is one thing, out there with all that noise and distraction is an altogether different thing and "stagefright" takes over sometimes. You do belong there, Uwe. You just need to develop skills, that's all. And the only way to get them is on-the-air. (www.oldradioparts.com) seems like a good source, I might buy from them sometimes, I still need a transformer for the little transmitter. By the way about specifying these transformers, to get those 320Volt with a tube rectifier do you need a centertapped transformer with roughly 160V in each winding, what they call a 160-0-160?? No! That will get you far less than what you need. With theoretically "perfect" rectifiers and transformers, the output voltage depends entirely on the type of filter and the transformer voltage. With a full-wave center-tap rectifier and a choke-input filter, the maximum voltage obtainable is 0.9 times the transformer voltage, and with a capacitor input filter, the maximum voltage obtainable is 1.414 times the transformer voltage. With the full-wave center-tap rectifier, "transformer voltage" means "each side of center tap". The above numbers assume perfect components whose ratings are big enough to do the job. With real world components, it's a little more complicated, but the results are always that you get less voltage. The AC-1 uses a capacitor-input filter and a 6X5GT rectifier. Also, the transformer is not "perfect" - just good enough to do the job. End result is that the transformer is about 320-0-320 and the resulting DC is about 325 volts. Easiest way to work with tube rectifiers is to look them up in the tube manuals (there are several tube manuals on-line) and look at the design curves. I did see these other AC-1 sites and yes I do use the smaller resistor parallel to the crystal. Excellent. May take some experimentation. btw, check out AF4K's website for crystal suppliers. I read a little more about chokes in old radio amateur handbooks and it seems that even their placement in the chassis can be tricky. I would love to know a way, because even with the 'new' choke the rig is not 'there' yet, to possibly make a test setup for this entire pi section and 'bench test it. Is there such a thing? Yes, but it's not necessary. You know the capacitors are the right ones, so it's merely a matter of the chokes and coil. If I terminate it with a 50 load and feed my HF generator signal on the input (plate) side this would not be appropriate because the tx and the test generator have a different output impedance?? That's exactly right. And what do you want the pi section to do, resonate at the transmitter frequency? Yes. But more than just resonate, it transforms the load impedance from 50 ohms to whatever the tube needs. Ways to go... Good luck & congrats again! 73 de Jim, N2EY |
Ok Folks, at the end of a long saga of fiddling with an old technology tube
transmitter is this bit of satifying news: A few days ago, I had a QSO with a fellow in Ohio, I received an email and mp3 sound file from a fellow in Leeds, England, who had heard and recorded my little 5 Watt signal and this way I could hear it too. He gave it a 429-539 QSB and listening to it I was embarrassed by the less than perfect code as well as the detectable chirp but oh well... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? Anyways, hints of where to find the circuit diagram are welcome. With a very chirpy 73 Uwe in article , Uwe at wrote on 4/8/04 4:42 PM: in article , N2EY at PAMNO wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe |
Ok Folks, at the end of a long saga of fiddling with an old technology tube
transmitter is this bit of satifying news: A few days ago, I had a QSO with a fellow in Ohio, I received an email and mp3 sound file from a fellow in Leeds, England, who had heard and recorded my little 5 Watt signal and this way I could hear it too. He gave it a 429-539 QSB and listening to it I was embarrassed by the less than perfect code as well as the detectable chirp but oh well... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? Anyways, hints of where to find the circuit diagram are welcome. With a very chirpy 73 Uwe in article , Uwe at wrote on 4/8/04 4:42 PM: in article , N2EY at PAMNO wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe |
Uwe wrote:
Ok Folks, at the end of a long saga of fiddling with an old technology tube transmitter is this bit of satifying news: A few days ago, I had a QSO with a fellow in Ohio, I received an email and mp3 sound file from a fellow in Leeds, England, who had heard and recorded my little 5 Watt signal and this way I could hear it too. He gave it a 429-539 QSB and listening to it I was embarrassed by the less than perfect code as well as the detectable chirp but oh well... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? Anyways, hints of where to find the circuit diagram are welcome. With a very chirpy 73 Uwe in article , Uwe at wrote on 4/8/04 4:42 PM: in article , N2EY at wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe See if you can get a copy of the ARRL Handbook from the '40s or '50s. '60s will get you some 807's, some 1625's (still cheaper than 807's at Antique Electronics Supply!), and some 6146's. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Uwe wrote:
Ok Folks, at the end of a long saga of fiddling with an old technology tube transmitter is this bit of satifying news: A few days ago, I had a QSO with a fellow in Ohio, I received an email and mp3 sound file from a fellow in Leeds, England, who had heard and recorded my little 5 Watt signal and this way I could hear it too. He gave it a 429-539 QSB and listening to it I was embarrassed by the less than perfect code as well as the detectable chirp but oh well... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? Anyways, hints of where to find the circuit diagram are welcome. With a very chirpy 73 Uwe in article , Uwe at wrote on 4/8/04 4:42 PM: in article , N2EY at wrote on 4/8/04 07:59: In article , Uwe writes: Using the L/C meter I wound a proper coil, I checked the calibration of my plate current meter, I did a more thorough check of the grid current (it is between 1 and 2 mA) and so on and so forth. I think you mean "screen current". And I did connect a dummy load (even though they don't respond or send out QSL cards when you tranmit into them). Yup! None of the thing did make any real difference and the dip, the elusive dip, was in the order of magnitude of maybe 2 mA, nearly impossible to see on my meter. Then I changed the circuit around as you suggested, testing the RFC and I got a dip the likes of which I had never seen. The meter went slowly from about 30 mA to 50 mA and then dropped to about 25 mA, I couldn't miss it. But what does it mean. I gather my RFC is not ok. What is wrong?? I used a Series 4590 high current filter inductor I had around, it has the Digi Key number DN 4528. The RFC you're using is not meant for the appliucation. It's intended for much lower frequencies. You can't tell that just by looking at it. RF choke design is a matter of compromises. For example, the use of a powdered iron or ferrite core will raise the inductance. But that same core does not work at all frequencies, and may saturate from DC current in the core. The biggest problem is called "distributed capacitance". In order to get lots of inductance, you put on lots of turns, closely spaced. But each turn has a small amount of capacitance to the turns next to it. All these small capacitances add up, and as the frequency is increased they become significant to the total reactance of the choke. At one or more frequencies the choke will actually resonate - these are called "self resonant" frequencies. At some frequencies the choke may act like an inductor of much lower inductance, or even like a capacitor, because of the self resonances. Self resonance in a choke can be found with a suitable dip meter. RF chokes that are meant for applications like the AC-1 are designed to have self-resonant frequencies far from the amateur bands. Happy about the dip but still not clear on the deeper reasons... Hope this helps. 73 de Jim, N2EY Yes this is all very helpful. Indeed I was thinking that it would have taken me a very long time to figure this out by myself, if at all. I put another choke in there, a Hammond 1535B, the self resonant min. frequ. is 1.3Mhz. I guess it does take some deeper inside what parameters to look for since this one improves things slightly but not yet altogether (slightly more pronounced dip). Who carries the sort of chokes you were refering to? 73 Uwe See if you can get a copy of the ARRL Handbook from the '40s or '50s. '60s will get you some 807's, some 1625's (still cheaper than 807's at Antique Electronics Supply!), and some 6146's. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
"Uwe" wrote in message ... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? You almost have to put those 807s in push-pull, for aesthetic reasons. That is easier to do with plug-in coils than with a bandswitch. Then you need a dual variable to tune the dual coils. Swinging link to adjust coupling to the antenna. This stuff shows up at hamfests sometimes. You may find someone's old homebrew rig for sale and you can salvage the parts from it. The Handbooks Tim mentioned will have all the info you need. I started out with a 1953 Handbook but I can't remember what projects were in it anymore. They're all over eBay, don't pay too much. Tim's also right about the 1625 tubes. They're the same as 807s except for the filament voltage and socket. My second transmitter (the first was a single 6V6) used an 807W, a compact version of the full-size bottle, as the PA. I used a Calumet baking soda can for a shield. While you're cruising the hamfests, look for an RCA Transmitting Tube manual, a small paperback. They're fun to read and there's some application info in them, as well as the usual datasheets. I used to use a mercury-wetted relay to key my tube rigs. They're really fast and make a nice ticking sound when you're keying. They also isolate you from the keyed voltage and allow the use of most modern keyers. Definitely in keeping with the period, too. They look like octal vacuum tubes with metal bulbs but they're shiny, not black. 24 VDC is a common coil voltage. Do you hang out on the boatanchors group? You might be able to turn up some parts and lots of info over there. (Note that I have quit trying to convert you to solid-state! You are obviously a lost cause. : Have fun.) 73, "PM" |
"Uwe" wrote in message ... So now is the time to start the construction of that more advanced version of a starter transmitter using two 807 as finals, who was mentioning that design way back?? You almost have to put those 807s in push-pull, for aesthetic reasons. That is easier to do with plug-in coils than with a bandswitch. Then you need a dual variable to tune the dual coils. Swinging link to adjust coupling to the antenna. This stuff shows up at hamfests sometimes. You may find someone's old homebrew rig for sale and you can salvage the parts from it. The Handbooks Tim mentioned will have all the info you need. I started out with a 1953 Handbook but I can't remember what projects were in it anymore. They're all over eBay, don't pay too much. Tim's also right about the 1625 tubes. They're the same as 807s except for the filament voltage and socket. My second transmitter (the first was a single 6V6) used an 807W, a compact version of the full-size bottle, as the PA. I used a Calumet baking soda can for a shield. While you're cruising the hamfests, look for an RCA Transmitting Tube manual, a small paperback. They're fun to read and there's some application info in them, as well as the usual datasheets. I used to use a mercury-wetted relay to key my tube rigs. They're really fast and make a nice ticking sound when you're keying. They also isolate you from the keyed voltage and allow the use of most modern keyers. Definitely in keeping with the period, too. They look like octal vacuum tubes with metal bulbs but they're shiny, not black. 24 VDC is a common coil voltage. Do you hang out on the boatanchors group? You might be able to turn up some parts and lots of info over there. (Note that I have quit trying to convert you to solid-state! You are obviously a lost cause. : Have fun.) 73, "PM" |
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