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Ameco AC-1 problem
I recently put together the old AC-1 tube transmitter for the 40 m band.
And it works, kind of. It oscillates nicely but does not have any power. I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. 73 Uwe |
It oscillates nicely but does not have any power.
I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. Did you do any voltage or current measurements? While I haven't played with a real AC-1, I've built many similar 6V6 single tube transmitters. I have the circuit for the AC-1, and it looks pretty similar to some I've built. First thing to do is measure the B+ to the plate and screen. Next, open the plate feed where it connects to the filter capacitor and insert a milliameter. With the "load" capacitor at maximum, adjust the "tune" capacitor for minimum current. Take a set of readings and get back to me. Doug Moore KB9TMY (Formerly K6HWY) |
It oscillates nicely but does not have any power.
I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. Did you do any voltage or current measurements? While I haven't played with a real AC-1, I've built many similar 6V6 single tube transmitters. I have the circuit for the AC-1, and it looks pretty similar to some I've built. First thing to do is measure the B+ to the plate and screen. Next, open the plate feed where it connects to the filter capacitor and insert a milliameter. With the "load" capacitor at maximum, adjust the "tune" capacitor for minimum current. Take a set of readings and get back to me. Doug Moore KB9TMY (Formerly K6HWY) |
In article , Uwe
writes: I recently put together the old AC-1 tube transmitter for the 40 m band. From a kit, or from your own collection of parts? It oscillates nicely but does not have any power. I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. How are you tuning it up and measuring the output power? I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. First thing is the voltages and currents, as already suggested. Then there's the size of the coil and your tuneup technique. What sort of load do you have connected to the output? 73 de Jim, N2EY |
In article , Uwe
writes: I recently put together the old AC-1 tube transmitter for the 40 m band. From a kit, or from your own collection of parts? It oscillates nicely but does not have any power. I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. How are you tuning it up and measuring the output power? I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. First thing is the voltages and currents, as already suggested. Then there's the size of the coil and your tuneup technique. What sort of load do you have connected to the output? 73 de Jim, N2EY |
Doug, thank you soo much for your email, you just fixed my transmitter.
Well, sort of. As I tried to do what you had suggested I noticed that someone (I could never have done such a thing) had connected the 18k resistor (which is connected to grid # 2 on one end) on the wrong end of the choke. I guess that choked it. Now we don't just have oscillations, there is even a little bite to it. I am relatively new to all this and I am just putting together the necessary equipment. So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. How do you monitor your transmitting tone with a device like this. Doug, thanks again, I am quite happy now Uwe KB1JOW in article , Troglodite at wrote on 3/11/04 14:26: It oscillates nicely but does not have any power. I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. Did you do any voltage or current measurements? While I haven't played with a real AC-1, I've built many similar 6V6 single tube transmitters. I have the circuit for the AC-1, and it looks pretty similar to some I've built. First thing to do is measure the B+ to the plate and screen. Next, open the plate feed where it connects to the filter capacitor and insert a milliameter. With the "load" capacitor at maximum, adjust the "tune" capacitor for minimum current. Take a set of readings and get back to me. Doug Moore KB9TMY (Formerly K6HWY) |
Doug, thank you soo much for your email, you just fixed my transmitter.
Well, sort of. As I tried to do what you had suggested I noticed that someone (I could never have done such a thing) had connected the 18k resistor (which is connected to grid # 2 on one end) on the wrong end of the choke. I guess that choked it. Now we don't just have oscillations, there is even a little bite to it. I am relatively new to all this and I am just putting together the necessary equipment. So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. How do you monitor your transmitting tone with a device like this. Doug, thanks again, I am quite happy now Uwe KB1JOW in article , Troglodite at wrote on 3/11/04 14:26: It oscillates nicely but does not have any power. I know, it is not supposed to have much power but this one is weaker than weak, the output couldn't drive any antenna. I was wondering if there are AC-1 owners/builders around here who could suggest a few things to try, who are knowlegable about this thing. Did you do any voltage or current measurements? While I haven't played with a real AC-1, I've built many similar 6V6 single tube transmitters. I have the circuit for the AC-1, and it looks pretty similar to some I've built. First thing to do is measure the B+ to the plate and screen. Next, open the plate feed where it connects to the filter capacitor and insert a milliameter. With the "load" capacitor at maximum, adjust the "tune" capacitor for minimum current. Take a set of readings and get back to me. Doug Moore KB9TMY (Formerly K6HWY) |
So a 50 resistor serves as my dummy load and a meter connected to
the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. How do you monitor your transmitting tone with a device like this. I run my 6V6's at about 325 volts on the plate, 250 on the screen. The plate is loaded to about 40ma, which is about 13 watts input. You can push it beyond this, but there's really no point since you have to quadruple your power to gain one S unit on the receiving end. You'll get about 8 watts out which is fine. If you want something heftier, you can go to a 6L6, 807 or 6146 tube. There is a compromise with single tube transmitters though, as the power goes up they tend to chirp, that is, the frequency slides a bit as they are keyed. It's not objectionable on the 6V6 transmitters, which is why I favor this power level. I started out in 1954 with a surplus ARC-5 receiver and a simple 6V6 transmitter. With it I gained code proficiency and managed to work 28 states before my Novice licence expired. (They were only good for a year back then.) For monitoring, you can just use your receiver with the antenna disconnected, or you can construct any number of monitor devices which you will find in the ARRL handbook. You can get more sophisticated but you don't have to. There is a special satisfaction in communicating with very simple equipment. Doug Moore KB9TMY |
So a 50 resistor serves as my dummy load and a meter connected to
the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. How do you monitor your transmitting tone with a device like this. I run my 6V6's at about 325 volts on the plate, 250 on the screen. The plate is loaded to about 40ma, which is about 13 watts input. You can push it beyond this, but there's really no point since you have to quadruple your power to gain one S unit on the receiving end. You'll get about 8 watts out which is fine. If you want something heftier, you can go to a 6L6, 807 or 6146 tube. There is a compromise with single tube transmitters though, as the power goes up they tend to chirp, that is, the frequency slides a bit as they are keyed. It's not objectionable on the 6V6 transmitters, which is why I favor this power level. I started out in 1954 with a surplus ARC-5 receiver and a simple 6V6 transmitter. With it I gained code proficiency and managed to work 28 states before my Novice licence expired. (They were only good for a year back then.) For monitoring, you can just use your receiver with the antenna disconnected, or you can construct any number of monitor devices which you will find in the ARRL handbook. You can get more sophisticated but you don't have to. There is a special satisfaction in communicating with very simple equipment. Doug Moore KB9TMY |
Uwe wrote in message ...
So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. E squared over R, yes, two watts is about right. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Seven watts input, two watts output is a bit low. How are you adjusting the controls? Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. IIRC that design called for 300 or 350 volts B+, which would work out to 15 watts or so input. The output network is not optimized for 200 volts B+, and in addition the efficieny is better with more plate voltage. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. What study methods are you using? How do you monitor your transmitting tone with a device like this. Several ways: 1) Connect an audio oscillator to the key so that both it and the transmitter are keyed at the same time. This can be a bit tricky because the two circuits must not interact. 2) Listen to the transmitted signal on your receiver when transmitting. This requires that you have a way of reducing the receiver gain while transmitting, but not completely silencing the receiver. What sort of receiver do you have to go with the transmitter? 73 de Jim, N2EY |
Uwe wrote in message ...
So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. E squared over R, yes, two watts is about right. All this at B+ of 200v and an anode current of about 35mA (I am running the transmitter off an adjustable bench tube power supply at this point). Seven watts input, two watts output is a bit low. How are you adjusting the controls? Does all this compare with the numbers you get with your transmitter?? I will need to build a power supply for the final version and would be interested to know what you use for B+. In order to get 5 Watts I would have to crank up the B+ quite a bit. IIRC that design called for 300 or 350 volts B+, which would work out to 15 watts or so input. The output network is not optimized for 200 volts B+, and in addition the efficieny is better with more plate voltage. Actually I don't care at this point since I am still practicing for my code exam, so I can't even use the transmitter right now. What study methods are you using? How do you monitor your transmitting tone with a device like this. Several ways: 1) Connect an audio oscillator to the key so that both it and the transmitter are keyed at the same time. This can be a bit tricky because the two circuits must not interact. 2) Listen to the transmitted signal on your receiver when transmitting. This requires that you have a way of reducing the receiver gain while transmitting, but not completely silencing the receiver. What sort of receiver do you have to go with the transmitter? 73 de Jim, N2EY |
So a 50 resistor serves as my dummy load and a meter connected to
the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. Uwe, The 10 Vrms that your meter indicates may not be accurate at 3.5 or 7 MHZ. It is probably OK at 60 hz. What you can derive from the 10 Vrms is that the AC-1 is producing power, just not sure how much. One thing you might try is a method to remove the frequency dependency of your measurements. Use a 10:1 voltage divider (10k and a 1.11k). Run this thru a Germanium or Schottky detector diode and a .01 filter capacitor. You now have a DC voltage that is proportional to power, and relatively frequency independent. To calculate the RMS voltage across the 50 ohm load: Read the DC volts out of the detector-Vdc. Then Vrms=(Vdc*.707)*10. Example: You read 2Vdc out of the detector. Vrms=14.14 volts. Power into the 50 ohm load is then: 14.14^2/50=4 Watts. The diode drop in the dector will introduce some error at QRP levels, hopefully not too much for what you are trying to do. 73 Gary N4AST |
So a 50 resistor serves as my dummy load and a meter connected to
the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. Uwe, The 10 Vrms that your meter indicates may not be accurate at 3.5 or 7 MHZ. It is probably OK at 60 hz. What you can derive from the 10 Vrms is that the AC-1 is producing power, just not sure how much. One thing you might try is a method to remove the frequency dependency of your measurements. Use a 10:1 voltage divider (10k and a 1.11k). Run this thru a Germanium or Schottky detector diode and a .01 filter capacitor. You now have a DC voltage that is proportional to power, and relatively frequency independent. To calculate the RMS voltage across the 50 ohm load: Read the DC volts out of the detector-Vdc. Then Vrms=(Vdc*.707)*10. Example: You read 2Vdc out of the detector. Vrms=14.14 volts. Power into the 50 ohm load is then: 14.14^2/50=4 Watts. The diode drop in the dector will introduce some error at QRP levels, hopefully not too much for what you are trying to do. 73 Gary N4AST |
Doug, that is much more power than I had hoped to get.
I am unsure about the max. values for the 6v6, therefore I stayed low. When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. And yes I have a few 807's lying around, so eventually I could build something more powerful, but at this point I need to work on my code, otherwise all of this is a mute point. You are right about monitoring the CW, it spills over to my receiver and I can monitor it there, even if I run the transmitter with a dummy load. So eventually I guess I could just use an arrangement that on transmitt I would automatically shorten out my receivers antenna. Hate to use a computer chip (for example) to do it though, I will have to look for a lower tech way to accomplish this switching. regards Uwe in article , Troglodite at wrote on 3/12/04 08:36: I run my 6V6's at about 325 volts on the plate, 250 on the screen. The plate is loaded to about 40ma, which is about 13 watts input. You can push it beyond this, but there's really no point since you have to quadruple your power to gain one S unit on the receiving end. You'll get about 8 watts out which is fine. If you want something heftier, you can go to a 6L6, 807 or 6146 tube. There is a compromise with single tube transmitters though, as the power goes up they tend to chirp, that is, the frequency slides a bit as they are keyed. It's not objectionable on the 6V6 transmitters, which is why I favor this power level. I started out in 1954 with a surplus ARC-5 receiver and a simple 6V6 transmitter. With it I gained code proficiency and managed to work 28 states before my Novice licence expired. (They were only good for a year back then.) For monitoring, you can just use your receiver with the antenna disconnected, or you can construct any number of monitor devices which you will find in the ARRL handbook. You can get more sophisticated but you don't have to. There is a special satisfaction in communicating with very simple equipment. Doug Moore KB9TMY |
In article , Uwe
writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY |
In article , Uwe
writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY |
in article , N2EY at
PAMNO wrote on 3/13/04 15:42: In article , Uwe writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY Jim, Sofar I have connected a scope to the antenna and tuned for max waveform eg. highest voltage. That is also the setting where my dummy load with bulbs is brightest. The original instructions for the AC1 explain how to tune but use expressions like 'turn the capacitor clockwise' which is useless to me when I am not using their exact part. They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Why do I tune for minimum current?? 73 Uwe KB1JOW |
in article , N2EY at
PAMNO wrote on 3/13/04 15:42: In article , Uwe writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY Jim, Sofar I have connected a scope to the antenna and tuned for max waveform eg. highest voltage. That is also the setting where my dummy load with bulbs is brightest. The original instructions for the AC1 explain how to tune but use expressions like 'turn the capacitor clockwise' which is useless to me when I am not using their exact part. They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Why do I tune for minimum current?? 73 Uwe KB1JOW |
"Uwe" wrote in message ... They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. It seems as though your Plate Tuning capacitor has too little capacitance to resonate at the frequency you are using. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Why do I tune for minimum current?? The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, which has its highest impedance at resonance. Therefore, when the two are resonant, current is at its lowest point. Tuning for maximum voltage on the antenna is not guaranteed to get the plate circuit on frequency, at least not the frequency you want. On many of those older tube transmitters, there was enough range in the plate tuning capacitor that the circuit could be tuned to the second harmonic of the desired frequency. Ie, if your desired frequency was 3500 kHz, the circuit could also be tuned to 7000 kHz. Measuring antenna voltage (which many cheap rigs did, by using a "Relative Output" meter, just an rf voltmeter connected across the antenna terminal) could lead you to adjust for the wrong resonance frequency. (In the 1960s the 80-meter Novice subband was 3.7-3.75 MHz, putting the second harmonic outside of any amateur band and generating a lot of QSL cards from the FCC for unsuspecting owners of transmitters like the Knight T-60, which had only a relative output meter.) If you can find someone who has a "dip meter," you can determine whether your plate circuit can be tuned to resonance, and, if not, how far off it is. A dip meter is an oscillator with an exposed coil, and an analog meter that dips when the oscillator is positioned near a resonant circuit. You adjust the dip meter knob until its meter dips and read the frequency off the dial. The dial calibration is not great, but if you have a general-coverage receiver you can listen for the oscillator signal. I would also investigate the coupling capacitor from the tube plate to the ungrounded terminal of the plate tuning capacitor. It may have dried out and shorted. Carefully measure for dc voltage from the ungrounded terminal of the plate tuning capacitor to the chassis. There shouldn't be any. If there is, replace the capacitor. As a rule of thumb, its voltage rating should be 4x the plate voltage, capacitance about 1000-1500 pF. "PM" |
"Uwe" wrote in message ... They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. It seems as though your Plate Tuning capacitor has too little capacitance to resonate at the frequency you are using. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Why do I tune for minimum current?? The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, which has its highest impedance at resonance. Therefore, when the two are resonant, current is at its lowest point. Tuning for maximum voltage on the antenna is not guaranteed to get the plate circuit on frequency, at least not the frequency you want. On many of those older tube transmitters, there was enough range in the plate tuning capacitor that the circuit could be tuned to the second harmonic of the desired frequency. Ie, if your desired frequency was 3500 kHz, the circuit could also be tuned to 7000 kHz. Measuring antenna voltage (which many cheap rigs did, by using a "Relative Output" meter, just an rf voltmeter connected across the antenna terminal) could lead you to adjust for the wrong resonance frequency. (In the 1960s the 80-meter Novice subband was 3.7-3.75 MHz, putting the second harmonic outside of any amateur band and generating a lot of QSL cards from the FCC for unsuspecting owners of transmitters like the Knight T-60, which had only a relative output meter.) If you can find someone who has a "dip meter," you can determine whether your plate circuit can be tuned to resonance, and, if not, how far off it is. A dip meter is an oscillator with an exposed coil, and an analog meter that dips when the oscillator is positioned near a resonant circuit. You adjust the dip meter knob until its meter dips and read the frequency off the dial. The dial calibration is not great, but if you have a general-coverage receiver you can listen for the oscillator signal. I would also investigate the coupling capacitor from the tube plate to the ungrounded terminal of the plate tuning capacitor. It may have dried out and shorted. Carefully measure for dc voltage from the ungrounded terminal of the plate tuning capacitor to the chassis. There shouldn't be any. If there is, replace the capacitor. As a rule of thumb, its voltage rating should be 4x the plate voltage, capacitance about 1000-1500 pF. "PM" |
In article ,
"Paul_Morphy" writes: The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, The AC-1 uses a pi network output circuit. 73 de Jim, N2EY |
In article ,
"Paul_Morphy" writes: The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, The AC-1 uses a pi network output circuit. 73 de Jim, N2EY |
In article , Uwe
writes: in article , N2EY at wrote on 3/13/04 15:42: In article , Uwe writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY Jim, Sofar I have connected a scope to the antenna and tuned for max waveform eg. highest voltage. That is also the setting where my dummy load with bulbs is brightest. The original instructions for the AC1 explain how to tune but use expressions like 'turn the capacitor clockwise' which is useless to me when I am not using their exact part. The tuneup procedure (adapted to your setup) is as follows: 1) Set both output capacitors to maximum capacitance (plates fully meshed) 2) Close the key and adjust the "plate" capacitor (the one nearest the tube in the circuit diagram) for minimum plate current. Maximum output should occur at the same time. Release the key. 3) Unmesh the "load" capacitor about 10 degrees or so 4) Repeat Step 2. The plate current minimum should be higher and there should be more output. 5) Repeat steps 2, 3, and 4 in order until you get maximum rated plate current at the minimum setting of the plate capacitor. They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. Then there is something wrong with your output circuit. What capacitors and coil are you using? The original design had a 365 pf variable "plate" capacitor and a similar capacitor for the "load" adjustment. The coil was different for each band. What components are you using in the output circuit? Plate tuning capacitor. coil, load capaticor, plate RF choke, coupling capacitor? Any of them could be the cause of your problem. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. That says to me that your plate C is too low. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Which should happen somewhere in the midrange of the plate capacitor adjustment. Why do I tune for minimum current?? Because that's when the impedance of the load circuit is closest to matching the tube's output. 73 de Jim, N2EY |
In article , Uwe
writes: in article , N2EY at wrote on 3/13/04 15:42: In article , Uwe writes: When I increase the plate voltage to 325V my 2. grid runs about 280V and the plate current increases to about 65 mA. I don't really dare to do that without knowing the max values on that tube. I guess I could lower the 2. grid voltage by increasing the value of the resistor connectd to it. I don't know if that would lower my plate current to what you get. Uwe, How are you tuning up the transmitter? Are you adjusting the plate capacitor for minimum current? 73 de Jim, N2EY Jim, Sofar I have connected a scope to the antenna and tuned for max waveform eg. highest voltage. That is also the setting where my dummy load with bulbs is brightest. The original instructions for the AC1 explain how to tune but use expressions like 'turn the capacitor clockwise' which is useless to me when I am not using their exact part. The tuneup procedure (adapted to your setup) is as follows: 1) Set both output capacitors to maximum capacitance (plates fully meshed) 2) Close the key and adjust the "plate" capacitor (the one nearest the tube in the circuit diagram) for minimum plate current. Maximum output should occur at the same time. Release the key. 3) Unmesh the "load" capacitor about 10 degrees or so 4) Repeat Step 2. The plate current minimum should be higher and there should be more output. 5) Repeat steps 2, 3, and 4 in order until you get maximum rated plate current at the minimum setting of the plate capacitor. They have an alternative way to tune by inserting a mA meter into the key lead but I do not get the little dips in current they are describing. Then there is something wrong with your output circuit. What capacitors and coil are you using? The original design had a 365 pf variable "plate" capacitor and a similar capacitor for the "load" adjustment. The coil was different for each band. What components are you using in the output circuit? Plate tuning capacitor. coil, load capaticor, plate RF choke, coupling capacitor? Any of them could be the cause of your problem. For me it is more of a linear increase in current from the highest capacity setting (lowest current) to the setting where the cap is all open and the current is highest. That says to me that your plate C is too low. The way things are the max output occurs more or less at the lowest anode current of my power supply (about 35mA at 200V B+). Which should happen somewhere in the midrange of the plate capacitor adjustment. Why do I tune for minimum current?? Because that's when the impedance of the load circuit is closest to matching the tube's output. 73 de Jim, N2EY |
"N2EY" wrote in message ... In article , "Paul_Morphy" writes: The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, The AC-1 uses a pi network output circuit. That's right, but the plate tuning cap and the inductor still operate as a parallel-resonant circuit. That's why plate current dips at resonance. In conjunction with the loading capacitor, the pi network also serves to match the plate impedance to the load impedance. 73, "PM" |
"N2EY" wrote in message ... In article , "Paul_Morphy" writes: The combination of the Plate Tuning capacitor and the inductor in the output circuit comprise a parallel-resonant tuned circuit, The AC-1 uses a pi network output circuit. That's right, but the plate tuning cap and the inductor still operate as a parallel-resonant circuit. That's why plate current dips at resonance. In conjunction with the loading capacitor, the pi network also serves to match the plate impedance to the load impedance. 73, "PM" |
"N2EY" wrote in message ... 2) Close the key and adjust the "plate" capacitor (the one nearest the tube in the circuit diagram) for minimum plate current. Maximum output should occur at the same time. It is a characteristic of pi-network amplifiers that efficiency and power output are slightly better when the plate is tuned slightly off resonance. Tuning for a dip is good enough for most purposes. Why do I tune for minimum current?? Because that's when the impedance of the load circuit is closest to matching the tube's output. If plate voltage is 200 and plate current is 35 mA, plate impedance is 200/0.035, or 5714 ohms. The impedance of the load has nothing to do with this, it is due to the reactance at resonance of the plate tuning capacitor and the coil, which are equal but opposite in phase. You can have an open circuit on the other side of the coil and still tune for a dip in plate current. Assuming stable plate voltage it is possible to have the same plate current over a wide range of load impedances. Because the pi network looks like a lumped section of transmission line, and because the plate tuning capacitor serves the dual functions of resonating the plate circuit _and_ matching the plate circuit to the input of the pi network, variations at the load end require slight adjustments of the plate tuning capacitor. To get maximum power transfer to the load, the pi network must transform the plate impedance to the load impedance, while also resonating the plate circuit. There's more going on than simple impedance matching. 73, "PM" |
"N2EY" wrote in message ... 2) Close the key and adjust the "plate" capacitor (the one nearest the tube in the circuit diagram) for minimum plate current. Maximum output should occur at the same time. It is a characteristic of pi-network amplifiers that efficiency and power output are slightly better when the plate is tuned slightly off resonance. Tuning for a dip is good enough for most purposes. Why do I tune for minimum current?? Because that's when the impedance of the load circuit is closest to matching the tube's output. If plate voltage is 200 and plate current is 35 mA, plate impedance is 200/0.035, or 5714 ohms. The impedance of the load has nothing to do with this, it is due to the reactance at resonance of the plate tuning capacitor and the coil, which are equal but opposite in phase. You can have an open circuit on the other side of the coil and still tune for a dip in plate current. Assuming stable plate voltage it is possible to have the same plate current over a wide range of load impedances. Because the pi network looks like a lumped section of transmission line, and because the plate tuning capacitor serves the dual functions of resonating the plate circuit _and_ matching the plate circuit to the input of the pi network, variations at the load end require slight adjustments of the plate tuning capacitor. To get maximum power transfer to the load, the pi network must transform the plate impedance to the load impedance, while also resonating the plate circuit. There's more going on than simple impedance matching. 73, "PM" |
Gary, you may be right regarding my power output measurement, but I thought
I knew how you calculate DC power and AC power of sinusoidial waveforms on my scope, which, by multiplying with 0.707 you have to reduce first to the aquivalent of a DC voltage. What confuses me in your suggestion (printed below) is that even after you rectify an AC signal and send it through a filter capacitor you STILL suggest to multiply it times 0.707. I would have thought that would give you the wrong result?? Where do I go wrong, if at all?? Uwe in article , JGBOYLES at wrote on 3/12/04 17:19: So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. Uwe, The 10 Vrms that your meter indicates may not be accurate at 3.5 or 7 MHZ. It is probably OK at 60 hz. What you can derive from the 10 Vrms is that the AC-1 is producing power, just not sure how much. One thing you might try is a method to remove the frequency dependency of your measurements. Use a 10:1 voltage divider (10k and a 1.11k). Run this thru a Germanium or Schottky detector diode and a .01 filter capacitor. You now have a DC voltage that is proportional to power, and relatively frequency independent. To calculate the RMS voltage across the 50 ohm load: Read the DC volts out of the detector-Vdc. Then Vrms=(Vdc*.707)*10. Example: You read 2Vdc out of the detector. Vrms=14.14 volts. Power into the 50 ohm load is then: 14.14^2/50=4 Watts. The diode drop in the dector will introduce some error at QRP levels, hopefully not too much for what you are trying to do. 73 Gary N4AST |
Gary, you may be right regarding my power output measurement, but I thought
I knew how you calculate DC power and AC power of sinusoidial waveforms on my scope, which, by multiplying with 0.707 you have to reduce first to the aquivalent of a DC voltage. What confuses me in your suggestion (printed below) is that even after you rectify an AC signal and send it through a filter capacitor you STILL suggest to multiply it times 0.707. I would have thought that would give you the wrong result?? Where do I go wrong, if at all?? Uwe in article , JGBOYLES at wrote on 3/12/04 17:19: So a 50 resistor serves as my dummy load and a meter connected to the dummy load indicates around 10 volts RMS. If I did my homework that would indicate around 2 watt output. Uwe, The 10 Vrms that your meter indicates may not be accurate at 3.5 or 7 MHZ. It is probably OK at 60 hz. What you can derive from the 10 Vrms is that the AC-1 is producing power, just not sure how much. One thing you might try is a method to remove the frequency dependency of your measurements. Use a 10:1 voltage divider (10k and a 1.11k). Run this thru a Germanium or Schottky detector diode and a .01 filter capacitor. You now have a DC voltage that is proportional to power, and relatively frequency independent. To calculate the RMS voltage across the 50 ohm load: Read the DC volts out of the detector-Vdc. Then Vrms=(Vdc*.707)*10. Example: You read 2Vdc out of the detector. Vrms=14.14 volts. Power into the 50 ohm load is then: 14.14^2/50=4 Watts. The diode drop in the dector will introduce some error at QRP levels, hopefully not too much for what you are trying to do. 73 Gary N4AST |
What confuses me in your suggestion (printed below) is that even after you
rectify an AC signal and send it through a filter capacitor you STILL suggest to multiply it times 0.707. I would have thought that would give you the wrong result?? Uwe, Wouldn't be the first time I was wrong. If you rectify and filter an AC waveform, and the read the DC voltage, this is Vpeak of the AC. In the example I gave, you read 2 vdc out of the detector circuit. Multiply this times the X10 divider, and you get 20vdc which is Vpeak across the 50 ohm load. To get the rms voltage across the load Vpeak*.707=20*.707=14.14 Vrms. 14.14Vrms across 50 ohms=4 watts. BTW, the reason I suggested a voltage divider (attenuator) rather than reading directly with a VOM or scope is to reduce the likelyhood of the scope probe or meter impedance from detuning the AC-1 causing further errors. If you are using a scope, measure the Vpeak across the 50 ohm resistor, multiply by .707 to get Vrms. 73 Gary N4AST |
What confuses me in your suggestion (printed below) is that even after you
rectify an AC signal and send it through a filter capacitor you STILL suggest to multiply it times 0.707. I would have thought that would give you the wrong result?? Uwe, Wouldn't be the first time I was wrong. If you rectify and filter an AC waveform, and the read the DC voltage, this is Vpeak of the AC. In the example I gave, you read 2 vdc out of the detector circuit. Multiply this times the X10 divider, and you get 20vdc which is Vpeak across the 50 ohm load. To get the rms voltage across the load Vpeak*.707=20*.707=14.14 Vrms. 14.14Vrms across 50 ohms=4 watts. BTW, the reason I suggested a voltage divider (attenuator) rather than reading directly with a VOM or scope is to reduce the likelyhood of the scope probe or meter impedance from detuning the AC-1 causing further errors. If you are using a scope, measure the Vpeak across the 50 ohm resistor, multiply by .707 to get Vrms. 73 Gary N4AST |
With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Uwe |
With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. But questions remain. I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. How can I minimize this and especially keep it from becoming more severe at higher outputs. Also, the circuit diagram for the tranmitter did not state the coil diameter of the pi network. The pi network still has me scratching my head. Coils with slight variations in diameter give dramatically different results. Also changing the air cap with one of an identical range can have a vast effect, which surprised me. Is this the "real world components" versus the theory??? Uwe |
I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch. Uwe- I can think of two reasons for the "chirp". You did not mention your receiver. It is possible that the strong signal from your nearby transmitter causes the receiver to change pitch. I assume your transmitter is crystal controlled, since that is similar to the 6V6 homebrew transmitter I started with back in 1955. By increasing voltage, the crystal current increases. There is an effect due to heating of the crystal that might cause a chirp. In the case of my old transmitter, I found that I could get more power output by changing the 6V6 to a 6L6, which has the same base diagram. However, one thing that happened along the way was that crystal current increased to the point that one of my crystals fractured and stopped working. Looking back, I realize that the increase in power by changing tubes and increasing voltage, may not have made a significant difference. If you double your power, the received signal only goes up half an S-Unit. Improving your antenna can make a bigger difference! I don't know about the waveform contraction. I doubt it is from overload of the scope, but it might be due to the tube being a little "soft" due to low cathode emission in the 6V6. 73, Fred, K4DII |
I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch. Uwe- I can think of two reasons for the "chirp". You did not mention your receiver. It is possible that the strong signal from your nearby transmitter causes the receiver to change pitch. I assume your transmitter is crystal controlled, since that is similar to the 6V6 homebrew transmitter I started with back in 1955. By increasing voltage, the crystal current increases. There is an effect due to heating of the crystal that might cause a chirp. In the case of my old transmitter, I found that I could get more power output by changing the 6V6 to a 6L6, which has the same base diagram. However, one thing that happened along the way was that crystal current increased to the point that one of my crystals fractured and stopped working. Looking back, I realize that the increase in power by changing tubes and increasing voltage, may not have made a significant difference. If you double your power, the received signal only goes up half an S-Unit. Improving your antenna can make a bigger difference! I don't know about the waveform contraction. I doubt it is from overload of the scope, but it might be due to the tube being a little "soft" due to low cathode emission in the 6V6. 73, Fred, K4DII |
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. Congratulations! Though it's been many years, I still remember when I made my first contact with a transmitter very similar to yours. (It was 1954) As for the chirp, this is partly the nature of single tube transmitters. You can minimize it with careful power supply design, and just the right amount of feedback on your oscillator, but a small amount will remain. The feedback is controlled by the ratio of the capacitors marked C7 and C9 in the original Ameco schematic. They form a "tap" on the cathode RF choke. Increasing C7 slightly or decreasing C9 slightly will increase the feedback. Different crystals will also react differently. 73, Doug Moore KB9TMY |
With the help of some folks here I did troubleshoot my AC-1 tube transmitter (using a 6V6) and got it working somehow. Since I passed my code test and had my first QSO using the transmitter and boy was that exciting. Congratulations! Though it's been many years, I still remember when I made my first contact with a transmitter very similar to yours. (It was 1954) As for the chirp, this is partly the nature of single tube transmitters. You can minimize it with careful power supply design, and just the right amount of feedback on your oscillator, but a small amount will remain. The feedback is controlled by the ratio of the capacitors marked C7 and C9 in the original Ameco schematic. They form a "tap" on the cathode RF choke. Increasing C7 slightly or decreasing C9 slightly will increase the feedback. Different crystals will also react differently. 73, Doug Moore KB9TMY |
"Uwe" wrote in message ... I monitor the output signal on my scope and notice that right after key down the waveform contract just a bit and the tone changes pitch. I guess this is called chirp. I normally use B+ 200V. If I increase the voltage lets say to 300V this effect becomes much more pronounced. I still use an external bench supply capable of much higher currents and I don't think it is a power supply weakness. In fact putting a VOM on the supply line shows no sag in my supply voltage. I think 200 V is enough. Someone here probably knows what the AC-1 design voltage was, but I'm sure it wasn't 300 V, and may be have more like 150 V. While the 6V6 can handle higher voltages, as a keyed crystal oscillator, you don't want to overdo it. You could fracture a crystal, too. There's quite a bit of AC-1 lore online. Use http://www.google.com/search?q=ameco+ac-1 to find it. I even found a copy of the original AC-1 manual, but it doesn't show circuit voltages. Congrats on getting your ticket and making your first QSO. Now it's time to put this antique away and build some safe, cool, solid-state gear! 73, "PM" |
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