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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 |
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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