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2 tube AM transmitter
4/17/2008 6:36:53 PMIan
Hi everyone, I found this schematic online

I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/17/2008 8:07:06 PMPeter G. Balazsy
As long as you use a polarized plug and make sure the ground is wired to circuit ground then you should be safe...as long as the outlet you use is properly wired as well.

Safest thing is to use an isolation transformer.

4/17/2008 9:16:09 PMIan
Is the ground the larger or smaller pin?

:As long as you use a polarized plug and make sure the ground is wired to circuit ground then you should be safe...as long as the outlet you use is properly wired as well.
:
:Safest thing is to use an isolation transformer.

4/17/2008 10:11:30 PMA Valid Name
:Is the ground the larger or smaller pin?

The ground is the round pin (or what looks like a half round from the AC wall outlet).

The narrow slot is considered "hot" and is where the alternating current power comes out. The wiring behind the outlet to this slot is usually black in the U.S.

The wide slot is considered the "common" and is supposed to be grounded. Using the white wire as a common grounded wire, means that everyone is working from the same zero voltage position.
Round hole

4/20/2008 1:29:20 AMPeter G. Balazsy
ME thinks that Mr. "A Valid Name" is a certain well known to be thin skinned resident of our northern neighbor country perhaps who can't really stay away and keeps reappearing incognito ?? ...aka "Z" perchance?
4/17/2008 10:12:14 PMTonyJ
The neutral wire is the wider of the two blades on a polarized plug. As Peter mentioned, verify that the wiring at your receptacle is correct.

:Is the ground the larger or smaller pin?
:
::As long as you use a polarized plug and make sure the ground is wired to circuit ground then you should be safe...as long as the outlet you use is properly wired as well.
::
::Safest thing is to use an isolation transformer.

4/17/2008 10:14:05 PMRobert Blakeley
:Is the ground the larger or smaller pin?
:


The "Ground" is the 3rd hole. The Neutral is the larger pin. The Hot is the smaller one. IF, it is wired correctly.

::As long as you use a polarized plug and make sure the ground is wired to circuit ground then you should be safe...as long as the outlet you use is properly wired as well.
::
::Safest thing is to use an isolation transformer.

4/17/2008 11:41:38 PMEdd








My preference is for back to back use of transformers to get the isolation, by virtue of the higher cost of a dedicated isolation transformer now-a-days.

Just get two.However, the second transformer ....derived B+ supply....doesn’t even have to be as high of a current rating as the first one being used for the 300 ma filament requirements and the driving the second one, and that’s not much of a pull at that !

Reference:





73's de Edd





4/18/2008 12:07:20 AMThomas Dermody
Be sure to still connect your two 6.3 volt filaments in series when connecting them to the 12.6 volt transformer.....as how Edd has the wiring lettered, it looks like he wants them in parallel......though he probably doesn't.

T.

4/18/2008 12:36:09 AMEdd






Ah yes…Sir Thomas, caught that just after releasing, and one can’t go backwards on correcting an initial post…just make addendas afterwards.

With the schematics separation of the filament supply windings on the back to back positioning, I couldn’t tie one filament lead into a tube filament like the original schematic did, thus the [B] designation at the top should be another [A], so that the two tube filaments get wired in series to be supplied by the 12VAC from the transformers center portion.

Of course, there is yet another option of using two like 6.3 secondary transformers, with the tubes wired in parallel.



73's de Edd





4/18/2008 9:47:47 AMLewis Linson
If you replace the 6J5 with a - dare I say it? - 1N4004/5/6 Silicon diode, you will have less filament current and higher Voltage on the other tube. I just don't like using audio tubes for rectifiers.
Lewis


:
:
:
:
:
:
:
:
:Ah yes…Sir Thomas, caught that just after releasing, and one can’t go backwards on correcting an initial post…just make addendas afterwards.
:
:With the schematics separation of the filament supply windings on the back to back positioning, I couldn’t tie one filament lead into a tube filament like the original schematic did, thus the [B] designation at the top should be another [A], so that the two tube filaments get wired in series to be supplied by the 12VAC from the transformers center portion.
:
:Of course, there is yet another option of using two like 6.3 secondary transformers, with the tubes wired in parallel.
:
:
:
:
:73's de Edd
:
:
:
:
:
:

4/18/2008 1:20:18 PMThomas Dermody
Audio tubes are okay as rectifiers, if they can handle the current, but they aren't exactly designed for the purpose. However, my one dead 6Z5 (or almost dead....has several filament shorts.....I can get both filaments to light, but not from the pins they're supposed to light from.....it's messed up), which is designed as a rectifier, actually has grids inside of it. Strange! The plates are a bit farther from the cathodes than, say, a 6X5. The grids probably serve to make the tube conduct like a close spaced rectifier. The grids are tied to the plates. I don't know if that decreases the chances of arcing or not, since the grids are close to the cathodes, and they are at the same potential as the plates....so they may as well be the plates, though they don't carry as much current as the plates. Strange to find grids in a rectifier, though.

A solid state diode will surely decrease power draw from the transformer (less filament current). Be sure to use 6 volt transformers in that case, or use a 12SA7 or 12A8 if you use a 12 volt transformer. You may have more hum with a solid state diode than you would with a tube. A 100 ohm resistor will probably cure the problem. You can also bypass the diode with a .01 to .05 MFD 400-600 WV capacitor.

T.

4/18/2008 4:41:38 PMIan
I have already built it with a single 12.6v 1.2amp tapped secondary, would another of these be suffecient, or could I buy the 450ma Model, and put that 1.2 amp in first and the 450ma second for the B voltage
4/18/2008 6:15:43 PMThomas Dermody
The 450 mA 12.6 volt transformer would probably be just fine for the B voltage. Did you get your transformer from Radio Shack? Those amperages sound like the ones Radio Shack sells. I used a 1.2 ampere unit and a 450 mA unit for the FM radio I built. They worked well. I built a voltage doubler circuit which gave me full wave rectification and over 200 volts, which came in handy. Since the radio had 5 tubes, I also used another 1.2 ampere transformer to feed the rest of the tubes. All fit nicely in a plastic box, with one transformer on top, and it cost less than buying a specialized transformer.

A 1.2 ampere unit and a 450 mA unit should be fine for your application.

T.

4/18/2008 6:45:17 PMLewis Linson
450 mA @ 12 Volts is around six Watts. That sounds plenty enough juice to me.
Lewis

:The 450 mA 12.6 volt transformer would probably be just fine for the B voltage. Did you get your transformer from Radio Shack? Those amperages sound like the ones Radio Shack sells. I used a 1.2 ampere unit and a 450 mA unit for the FM radio I built. They worked well. I built a voltage doubler circuit which gave me full wave rectification and over 200 volts, which came in handy. Since the radio had 5 tubes, I also used another 1.2 ampere transformer to feed the rest of the tubes. All fit nicely in a plastic box, with one transformer on top, and it cost less than buying a specialized transformer.
:
:A 1.2 ampere unit and a 450 mA unit should be fine for your application.
:
:T.

4/18/2008 7:56:26 PMIan
Yes these are from radioshack, and I will Put it together and test it tomarrow. Thanks for the help.
4/18/2008 8:58:15 PMLewis Linson

To answer your original question, tho, having one side of the power line connect to the shield of an input device, could be a real bummer. Of the two prongs on a normal outlet, the narrow one is the "hot", and the wide one is "neutral". The neutral carries power, and the ground doesn't. The ground and neutral will, at some place, connect to the water pipe. The big round ground pin is run on a seperate conductor, so if there is a malfunction, the fuse or circuit breaker operates and no one gets shocked. There is also a ground fault circuit interrupter, which measures the current on the hot and neutral leads, and if it sees an unbalance (like you're in the tub and James Bond throws a space heater in, the GFCI trips and you get to shoot him anyway)

Lewis

P S Goldfinger, wasn't it?

LL


:Yes these are from radioshack, and I will Put it together and test it tomarrow. Thanks for the help.

4/18/2008 10:48:08 PMNorm Leal
Hi Ian

This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.

Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.

You can find information on small transmitters here:

http://antiqueradios.com/forums/viewforum.php?f=12

Norm

:Hi everyone, I found this schematic online
:
:
:
:I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/18/2008 11:08:09 PMIan
I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
:Hi Ian
:
: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
:
: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
:
: You can find information on small transmitters here:
:
:http://antiqueradios.com/forums/viewforum.php?f=12
:
:Norm
:
::Hi everyone, I found this schematic online
::
::
::
::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?
4/18/2008 11:22:51 PMNorm Leal
Hi Ian

The cathode, 1st and 2nd grids make up the oscillator circuit. 2nd grid acts as a plate. If you were to use a 6J5 for the oscillator and feed the signal into grid #1 of the 6SA7 your transmitter would be much more stable. B+ could be connected directly to grid #2. Rest of the circuit would stay the same.

Now all you need is another 6J5 as an audio amplifier. Feeding audio directly to grid #3 doesn't give much gain. This would be ok if you already have a large audio signal, more than several volts.

I used an audio output transformer in reverse for amplification. See 6888 transmitters under Homebrew at antiqueradios.com.

Norm

:I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
::Hi Ian
::
:: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
::
:: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
::
:: You can find information on small transmitters here:
::
::http://antiqueradios.com/forums/viewforum.php?f=12
::
::Norm
::
:::Hi everyone, I found this schematic online
:::
:::
:::
:::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/19/2008 12:10:02 AMIan
:Hi Ian
:Is this correct or is the plate connected somewhere else?


: The cathode, 1st and 2nd grids make up the oscillator circuit. 2nd grid acts as a plate. If you were to use a 6J5 for the oscillator and feed the signal into grid #1 of the 6SA7 your transmitter would be much more stable. B+ could be connected directly to grid #2. Rest of the circuit would stay the same.
:
: Now all you need is another 6J5 as an audio amplifier. Feeding audio directly to grid #3 doesn't give much gain. This would be ok if you already have a large audio signal, more than several volts.
:
: I used an audio output transformer in reverse for amplification. See 6888 transmitters under Homebrew at antiqueradios.com.
:
:Norm
:
:
:
::I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
:::Hi Ian
:::
::: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
:::
::: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
:::
::: You can find information on small transmitters here:
:::
:::http://antiqueradios.com/forums/viewforum.php?f=12
:::
:::Norm
:::
::::Hi everyone, I found this schematic online
::::
::::
::::
::::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/19/2008 12:19:32 AMIan
::Hi Ian
::Is this correct or is the plate connected somewhere else?
:
:
:


:: The cathode, 1st and 2nd grids make up the oscillator circuit. 2nd grid acts as a plate. If you were to use a 6J5 for the oscillator and feed the signal into grid #1 of the 6SA7 your transmitter would be much more stable. B+ could be connected directly to grid #2. Rest of the circuit would stay the same.
::
:: Now all you need is another 6J5 as an audio amplifier. Feeding audio directly to grid #3 doesn't give much gain. This would be ok if you already have a large audio signal, more than several volts.
::
:: I used an audio output transformer in reverse for amplification. See 6888 transmitters under Homebrew at antiqueradios.com.
::
::Norm
::
::
::
:::I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
::::Hi Ian
::::
:::: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
::::
:::: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
::::
:::: You can find information on small transmitters here:
::::
::::http://antiqueradios.com/forums/viewforum.php?f=12
::::
::::Norm
::::
:::::Hi everyone, I found this schematic online
:::::
:::::
:::::
:::::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/19/2008 12:21:34 AMIan (photo)

:::Is this correct or is the plate connected somewhere else?
::

This is the link

http://img294.imageshack.us/img294/8260/3tubetransmitterco9.gif
::
:
:
::: The cathode, 1st and 2nd grids make up the oscillator circuit. 2nd grid acts as a plate. If you were to use a 6J5 for the oscillator and feed the signal into grid #1 of the 6SA7 your transmitter would be much more stable. B+ could be connected directly to grid #2. Rest of the circuit would stay the same.
:::
::: Now all you need is another 6J5 as an audio amplifier. Feeding audio directly to grid #3 doesn't give much gain. This would be ok if you already have a large audio signal, more than several volts.
:::
::: I used an audio output transformer in reverse for amplification. See 6888 transmitters under Homebrew at antiqueradios.com.
:::
:::Norm
:::
:::
:::
::::I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
:::::Hi Ian
:::::
::::: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
:::::
::::: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
:::::
::::: You can find information on small transmitters here:
:::::
:::::http://antiqueradios.com/forums/viewforum.php?f=12
:::::
:::::Norm
:::::
::::::Hi everyone, I found this schematic online
::::::
::::::
::::::
::::::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/19/2008 9:33:14 AMNorm Leal
Ian

The idea will work but you need a few changes. 6SA7 cathode has to return to B-. Connections from the coil should only go to the new 6J5 tube. Coil connections should be removed from the 6SA7. Connect output of the 6J5 to grid #1 of 6SA7 through a small cap, 50 - 100pf. Then add a 47K resistor from grid #1 of 6SA7 to B-.

Might help if you draw the osc circuit, away from the 6SA7, connected only to your 6J5.

Norm

:
::::Is this correct or is the plate connected somewhere else?
:::
:
:This is the link
:
:http://img294.imageshack.us/img294/8260/3tubetransmitterco9.gif
:::
::
::
:::: The cathode, 1st and 2nd grids make up the oscillator circuit. 2nd grid acts as a plate. If you were to use a 6J5 for the oscillator and feed the signal into grid #1 of the 6SA7 your transmitter would be much more stable. B+ could be connected directly to grid #2. Rest of the circuit would stay the same.
::::
:::: Now all you need is another 6J5 as an audio amplifier. Feeding audio directly to grid #3 doesn't give much gain. This would be ok if you already have a large audio signal, more than several volts.
::::
:::: I used an audio output transformer in reverse for amplification. See 6888 transmitters under Homebrew at antiqueradios.com.
::::
::::Norm
::::
::::
::::
:::::I have extra tube sockets and some 6j5's If you can tell me how to make this work better please do. Am I correct that the oscilater part of the 6sa7 is the cathode and first grid, and this would then become the new 6j5?
::::::Hi Ian
::::::
:::::: This type of circuit is called a phono oscillator. It will work but not very well. The oscillator is free running and modulated by audio. Very much modulation causes FM distortion. Keep modulation low and you should be ok.
::::::
:::::: Later you could try separate oscillator and modulator tubes. A crystal controlled oscillator also works well.
::::::
:::::: You can find information on small transmitters here:
::::::
::::::http://antiqueradios.com/forums/viewforum.php?f=12
::::::
::::::Norm
::::::
:::::::Hi everyone, I found this schematic online
:::::::
:::::::
:::::::
:::::::I built this and was wondering because one side of the 120vac line is going to the input, could this harm the input device such as a cd player, or computer?

4/20/2008 12:13:02 AMIan
Ok I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.

Here's the link

http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 11:55:06 AMIan
Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.

Or it is here
http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif

I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
:
:Here's the link
:
:http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 1:19:29 PMLewis Linson


How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
Lewis


: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
:
:
:Or it is here
:http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
:
:I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
::
::Here's the link
::
::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 2:02:35 PMNorm Leal
Still a few strange things. In addition to audio input going directly to B+ there are several other problems. 6J5 plate is tied directly to B+ although you are trying to take a signal off the pin to drive 6SA7. Oscillator coil needs to return to plate of 6J5 not 6SA7. Then you wouldn't have this problem. Input pin of 6SA7 needs a grid resistor to B-.

Here are things to think about. When using a grid as input it can't return directly to a voltage but must be biased to a voltage through a resistor. Plate is output. When used as output it can't return directly to a voltage.

Ideally the 6SA7 should have a tuned plate circuit. For now you can use a resistor. It won't be tuned but the oscillator will determine frequency.

Norm

:
:
:
:How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
:Lewis
:
:
:: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
::
::
::Or it is here
::http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
::
::I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
:::
:::Here's the link
:::
:::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 3:22:59 PMIan
OK,I think I understand it better now. The .1 uf cap will keep the b+ off the audio, the grid resistor will
bias the 6sa7 (What value would this be, 4.7k?) The new output to antenna is the plate of the 6sa7(Dose this go to the b+ through a resistor, What value?)
The Bias resistor is now connecting the output of the 100pf cap(blocking B+) and the B- correct?

New drawing


:Still a few strange things. In addition to audio input going directly to B+ there are several other problems. 6J5 plate is tied directly to B+ although you are trying to take a signal off the pin to drive 6SA7. Oscillator coil needs to return to plate of 6J5 not 6SA7. Then you wouldn't have this problem. Input pin of 6SA7 needs a grid resistor to B-.
:
:Here are things to think about. When using a grid as input it can't return directly to a voltage but must be biased to a voltage through a resistor. Plate is output. When used as output it can't return directly to a voltage.
:
:Ideally the 6SA7 should have a tuned plate circuit. For now you can use a resistor. It won't be tuned but the oscillator will determine frequency.
:
:Norm
:
::
::
::
::How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
::Lewis
::
::
::: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
:::
:::
:::Or it is here
:::http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
:::
:::I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
::::
::::Here's the link
::::
::::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 4:52:50 PMNorm Leal
Ian

I would make the grid resistor 47K. Should be able to add a 4.7K plate resistor to B+.

Biggest problem I see now is audio being fed to B+. The added cap really doesn't help. This part of the circuit should stay the same as original.

I see what happened. You fed oscillator into grid #3 instead of grid #1. Why not feed audio directly to grid #1. It will take less signal to drive the tube. That way you don't need the .1 mf or 100K resistor. The 47K grid resistor will do the job.

Norm

:OK,I think I understand it better now. The .1 uf cap will keep the b+ off the audio, the grid resistor will
:bias the 6sa7 (What value would this be, 4.7k?) The new output to antenna is the plate of the 6sa7(Dose this go to the b+ through a resistor, What value?)
:The Bias resistor is now connecting the output of the 100pf cap(blocking B+) and the B- correct?
:
:New drawing
:
:
:
:
::Still a few strange things. In addition to audio input going directly to B+ there are several other problems. 6J5 plate is tied directly to B+ although you are trying to take a signal off the pin to drive 6SA7. Oscillator coil needs to return to plate of 6J5 not 6SA7. Then you wouldn't have this problem. Input pin of 6SA7 needs a grid resistor to B-.
::
::Here are things to think about. When using a grid as input it can't return directly to a voltage but must be biased to a voltage through a resistor. Plate is output. When used as output it can't return directly to a voltage.
::
::Ideally the 6SA7 should have a tuned plate circuit. For now you can use a resistor. It won't be tuned but the oscillator will determine frequency.
::
::Norm
::
:::
:::
:::
:::How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
:::Lewis
:::
:::
:::: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
::::
::::
::::Or it is here
::::http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
::::
::::I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
:::::
:::::Here's the link
:::::
:::::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 8:34:18 PMIan
I changed the input grid to grid #1,added the plate resistor, removed the 100k reistor and the .1 mfd cap.
The audio input still has b+ on one side and b- on the other wont this blow it? How can I change this?


:
: I would make the grid resistor 47K. Should be able to add a 4.7K plate resistor to B+.
:
: Biggest problem I see now is audio being fed to B+. The added cap really doesn't help. This part of the circuit should stay the same as original.
:
: I see what happened. You fed oscillator into grid #3 instead of grid #1. Why not feed audio directly to grid #1. It will take less signal to drive the tube. That way you don't need the .1 mf or 100K resistor. The 47K grid resistor will do the job.
:
:Norm
:
::OK,I think I understand it better now. The .1 uf cap will keep the b+ off the audio, the grid resistor will
::bias the 6sa7 (What value would this be, 4.7k?) The new output to antenna is the plate of the 6sa7(Dose this go to the b+ through a resistor, What value?)
::The Bias resistor is now connecting the output of the 100pf cap(blocking B+) and the B- correct?
::
::New drawing
::
::
::
::
:::Still a few strange things. In addition to audio input going directly to B+ there are several other problems. 6J5 plate is tied directly to B+ although you are trying to take a signal off the pin to drive 6SA7. Oscillator coil needs to return to plate of 6J5 not 6SA7. Then you wouldn't have this problem. Input pin of 6SA7 needs a grid resistor to B-.
:::
:::Here are things to think about. When using a grid as input it can't return directly to a voltage but must be biased to a voltage through a resistor. Plate is output. When used as output it can't return directly to a voltage.
:::
:::Ideally the 6SA7 should have a tuned plate circuit. For now you can use a resistor. It won't be tuned but the oscillator will determine frequency.
:::
:::Norm
:::
::::
::::
::::
::::How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
::::Lewis
::::
::::
::::: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
:::::
:::::
:::::Or it is here
:::::http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
:::::
:::::I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
::::::
::::::Here's the link
::::::
::::::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 10:22:40 PMNorm Leal
Ian

Unless I'm missing something only one more change. Remove the audio input which is going to B+ and connect it to Grid #3 of the 6SA7.

Norm

:I changed the input grid to grid #1,added the plate resistor, removed the 100k reistor and the .1 mfd cap.
:The audio input still has b+ on one side and b- on the other wont this blow it? How can I change this?
:
:
::
:: I would make the grid resistor 47K. Should be able to add a 4.7K plate resistor to B+.
::
:: Biggest problem I see now is audio being fed to B+. The added cap really doesn't help. This part of the circuit should stay the same as original.
::
:: I see what happened. You fed oscillator into grid #3 instead of grid #1. Why not feed audio directly to grid #1. It will take less signal to drive the tube. That way you don't need the .1 mf or 100K resistor. The 47K grid resistor will do the job.
::
::Norm
::
:::OK,I think I understand it better now. The .1 uf cap will keep the b+ off the audio, the grid resistor will
:::bias the 6sa7 (What value would this be, 4.7k?) The new output to antenna is the plate of the 6sa7(Dose this go to the b+ through a resistor, What value?)
:::The Bias resistor is now connecting the output of the 100pf cap(blocking B+) and the B- correct?
:::
:::New drawing
:::
:::
:::
:::
::::Still a few strange things. In addition to audio input going directly to B+ there are several other problems. 6J5 plate is tied directly to B+ although you are trying to take a signal off the pin to drive 6SA7. Oscillator coil needs to return to plate of 6J5 not 6SA7. Then you wouldn't have this problem. Input pin of 6SA7 needs a grid resistor to B-.
::::
::::Here are things to think about. When using a grid as input it can't return directly to a voltage but must be biased to a voltage through a resistor. Plate is output. When used as output it can't return directly to a voltage.
::::
::::Ideally the 6SA7 should have a tuned plate circuit. For now you can use a resistor. It won't be tuned but the oscillator will determine frequency.
::::
::::Norm
::::
:::::
:::::
:::::
:::::How 'bout a .1uFd cap right at the audio input? Looks like B+ leaving on the input.
:::::Lewis
:::::
:::::
:::::: Forgot to Connect the 2nd grid to B+ here is the new drawing. I also got the 450ma transformer, and 2 100pf caps 50wvdc.
::::::
::::::
::::::Or it is here
::::::http://img353.imageshack.us/img353/5586/3tubetransmittter2ez8.gif
::::::
::::::I redrew it, but now the b+ and and b- are tied together across the 100k resistor and the audio input. Is this correct and will this hurt the audio input device? Sorry for all the questions but Im new to this.
:::::::
:::::::Here's the link
:::::::
:::::::http://img232.imageshack.us/img232/9866/3tubetransmittter2wg5.gif

4/20/2008 10:27:59 PMIan
Thank you for helping me with this I will start building it tomorrow And then post results when tested.

4/20/2008 11:37:30 PMThomas Dermody
Seems to look pretty good. However, the large part of the oscillator coil should be to the right, and the small part should be to the left--the large part should be in the grid circuit, and the small part in the plate circuit.

Also, the resistor in the audio circuit should more likely be 470K or perhaps around 1 meg for good bass response. If you are feeding from a low impedance output (speaker output), the 47K won't ruin the bass much, but if you are using a line level output, it will significantly affect bass response, as well as overall gain. Also, it would be wise to use a .02 to .05 MFD cap between the audio input and grid 3 to prevent improper grid bias caused by unisolated transistorized outputs, where DC voltages are present. If you use a capacitor (recommended), you should definitely increase the grid resistance, idealy to 1 meg. For good bass response and gain, use the highest resistance permissable. If 5 meg works, and you like it better than 1 meg, use 5 meg, though 1 meg will probably be adequate.

T.

4/21/2008 12:34:01 AMPeter G. Balazsy
Isn't the filament feed still wrong?

Three 6v tubes in parallel on a 12v transformer?

4/21/2008 12:43:54 AMPeter G. Balazsy
correction ...two in parallel (6sa7 + 6j5) and those two in series with another 6j5 ?
4/21/2008 6:53:39 AMBob E.
:correction ...two in parallel (6sa7 + 6j5) and those two in series with another 6j5 ?

Ohm's law is not your strongest point I see.

4/21/2008 1:11:58 PMIan
Yes 2 in parallel in series with another. This should be ok right?

::correction ...two in parallel (6sa7 + 6j5) and those two in series with another 6j5 ?
:
:Ohm's law is not your strongest point I see.
:
:

4/21/2008 2:13:21 PMTonyJ
Hmmm now I'm scratching my head wondering if this will work. While the filaments will have the correct voltage on them, the paralleled tubes will only receive half of their filament current. According to Kirchoff's law, the current entering a junction must equal the current exiting. Assuming that the unparalleled 6J5 will have 300mA of filament current, each of the paralled tubes will share 300mA. This may or may not be an issue - maybe someone can chime in and clear this up in my mind.

:Yes 2 in parallel in series with another. This should be ok right?
:
:::correction ...two in parallel (6sa7 + 6j5) and those two in series with another 6j5 ?
::
::Ohm's law is not your strongest point I see.
::
::

4/21/2008 2:19:57 PMBob E.
:Yes 2 in parallel in series with another. This should be ok right?

You can't series unequal current branches. Two tubes in parallel equal 600ma, in series with a 300ma heater will definitely not work. You must equal each branch of the circuit _current_ wise. One solution would be to add a resistor in parallel with the single tube to equal current draw of the previous parallel branch.

6.3V/0.3A = 21ohms/1.89W resistor (use higher wattage as a safety margin).

Or use a 12AX7 in lieu the two 6J5 and use the heater in 6.3V mode which draws 0.3A and series it with the 12SA7.

4/21/2008 2:24:56 PMBob E.
:Or use a 12AX7 in lieu the two 6J5 and use the heater in 6.3V mode which draws 0.3A and series it with the 12SA7.

Typo correction:
Make that 6SA7, not 12SA7 as per your circuit.

4/21/2008 3:15:42 PMIan
I found a 6w 21ohm resistor that in now in series with the filiment of the 2nd 6j5.

The 100pf caps I have are only rated at 50wvdc, and they are on the b+ ,120vdc if I put them in series, 50pf at 100wvdc will they hold?

4/21/2008 4:01:58 PMkcj
so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?

:I found a 6w 21ohm resistor that in now in series with the filiment of the 2nd 6j5.
:
:The 100pf caps I have are only rated at 50wvdc, and they are on the b+ ,120vdc if I put them in series, 50pf at 100wvdc will they hold?

4/21/2008 4:16:25 PMIan
Yes
It is now completely built expect for the audio input which I am installing now. 100 pf cap is still not In because I am not sure if it will hold the B+

The 100pf caps I have are only rated at 50wvdc, and they are on the b+ ,120vdc if I put them in series, 50pf at 100wvdc will they hold?

:so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?
:
::I found a 6w 21ohm resistor that in now in series with the filiment of the 2nd 6j5.
::
::

4/21/2008 8:36:40 PMBob E.
:The 100pf caps I have are only rated at 50wvdc, and they are on the b+ ,120vdc if I put them in series, 50pf at 100wvdc will they hold?


I fail to find the 100pf cap in your schematic. I see a 56 and a 150pf. Does the cap has full DC supply across it ? I might work just for testing purpose and a short period though.

4/21/2008 8:34:13 PMBob E.
:so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?

No, he has two tubes in _parallel_ which are in series with another tube having a resistor in parallel. The OP is using 3 tubes in total.

4/21/2008 8:52:05 PMIan
The 100pf cap is between the plate of the 6j5 and the grid of the 6sa7.

The tubes are wired

A----*---*--B
A-\/\/\/-*--B

* = filiment
\/\/\/\ = resistor

::so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?
:
:No, he has two tubes in _parallel_ which are in series with another tube having a resistor in parallel. The OP is using 3 tubes in total.

4/21/2008 9:16:48 PMIan
How do I determine what the voltage rating for a ceramic capacitor is?

I have a 68pf cap that I could use for the 100pf, the 68 has no voltage marked.
The 22 pf cap is made of 3 capacitors
-||--||-
---||---
And measures 22pf on my capacitor tester,these have no volatge marking either, and the 56 pf cap is an old 50 pf molded mica
:The 100pf cap is between the plate of the 6j5 and the grid of the 6sa7.
:
:The tubes are wired
:
: A----*---*--B
: A-\/\/\/-*--B
:
:* = filiment
:\/\/\/\ = resistor
:
:::so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?
::
::No, he has two tubes in _parallel_ which are in series with another tube having a resistor in parallel. The OP is using 3 tubes in total.

4/21/2008 10:37:12 PMIan
Is the value of the antenna cap critical?
Because I found a 7.5 pf cap at 1kv, a 10 pf cap a 4kv, and a 100pf at 2kv(value determined by capacitor tester and reading) would the 7.5pf and the 10pf in series be sutible?

:How do I determine what the voltage rating for a ceramic capacitor is?
:
:I have a 68pf cap that I could use for the 100pf, the 68 has no voltage marked.
: The 22 pf cap is made of 3 capacitors
: -||--||-
: ---||---
:And measures 22pf on my capacitor tester,these have no volatge marking either, and the 56 pf cap is an old 50 pf molded mica
::The 100pf cap is between the plate of the 6j5 and the grid of the 6sa7.
::
::The tubes are wired
::
:: A----*---*--B
:: A-\/\/\/-*--B
::
::* = filiment
::\/\/\/\ = resistor
::
::::so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?
:::
:::No, he has two tubes in _parallel_ which are in series with another tube having a resistor in parallel. The OP is using 3 tubes in total.

4/21/2008 10:53:47 PMkcl
same thing. if you draw it in ladder logic form with the two rungs being the 12vac supply, electrically the same whether you series two parallel sets of components or consider them two separate series connected rungs.

::so now you should have 2 tube heaters in series across the xformer, and the single tube with a resistor in series across the xformer. correct?
:
:No, he has two tubes in _parallel_ which are in series with another tube having a resistor in parallel. The OP is using 3 tubes in total.

4/22/2008 5:38:44 PMEdd








Boy – oh -boooooy what a lot of responses you got ….and probably on one of the harder things to troubleshoot when things don’t work right when it is hooked up. I assume that you finally went with the back to back transformers. Plus the units filaments might have ended up different than I have shown…I like same tube types paired.

As for the 100 pf osc plate to grid capacitor coupling, if you haven’t tried it yet, at that voltage involved, I also had a similar situation over a weekend but I happen to have Hi-pot test capability up to 6KV so I just hooked up that ceramic unit that I had and stopped when I had reached 500V…not to worry !

I certainly will note that was also a low capacitance unit and one certainly could not expect the same situation on some .01-.1 ufd units with their inherently smaller dielectric spacing’s.

At one time I checked in and you certainly had a dreadful bed full of circuit errors, I finally tuned in again after the last circuit shown, and now, the final thing I might wonder is if you are really going to be needing that 6SA7 to be geared towards more
RF effectiveness or audio amplification in accordance to which way it is hooked up.

If you get the unit working like the hookup shown, you might then try it in a different manner to see which way works the best for you as respective to the units RF performance or modulation effect.

Note that there are two magenta breaks at the side of 6SA7 grid circuitry; the idea is to break in at that point and swap the grid connections to the circuitry. That will leave ALL of the associative biasing resistors and coupling the same, with just solely the particular grids involved, being swapped. In that manner the audio going into the 1st grid may make the audio requirement less.. its also isolated from the oscillator, so there wouldn’t be the situation of squegging / FM’ing the oscillator frequency, like one is up against when trying to modulate an oscillator circuit solely. There is still RF gain thru the system by the other grid and you may not need all of that 100 pf of coupling..ideally one could use a variable mica compression capacitor to find optimization of that coupling degree.



Redrawn Circuit Reference:



73's de Edd




4/22/2008 6:59:51 PMBob E.
:Boy – oh -boooooy what a lot of responses you got ….and probably on one of the harder things to troubleshoot when things don’t work right when it is hooked up.

For some reason I find this reply quite presomptuous. You're not the only one "qualified" on this board. It could be that I misread you reply.

I would advise the OP to replace the first 6J5 with a ss diode using a .01uF in parallel to avoid hum caused by RF riding on the AC wave and finding it's way in the circuit.

It just doesn't make sense to use a single tube as a rectifier. Powerwise and spacewise.

As for the rest, I couldn't find the OP's _three_ tubes schematic, hard to help and correct design errors. I do find your reply more complete including a redrawn schematic though.

4/22/2008 7:55:29 PMkcl
bob you really have a nasty attitude. who died and made you electronics king?

::Boy – oh -boooooy what a lot of responses you got ….and probably on one of the harder things to troubleshoot when things don’t work right when it is hooked up.
:
:For some reason I find this reply quite presomptuous. You're not the only one "qualified" on this board. It could be that I misread you reply.
:
:I would advise the OP to replace the first 6J5 with a ss diode using a .01uF in parallel to avoid hum caused by RF riding on the AC wave and finding it's way in the circuit.
:
:It just doesn't make sense to use a single tube as a rectifier. Powerwise and spacewise.
:
:As for the rest, I couldn't find the OP's _three_ tubes schematic, hard to help and correct design errors. I do find your reply more complete including a redrawn schematic though.

4/22/2008 8:31:24 PMPeter G. Balazsy
Bob:
I agree... why must you be so abrasive and or critical of others?

Everyone's well intended contributions are always appreciated around here ....and if you go on attacking these nice helpful guys it can only serve to make them feel somewhat intimidated .......and makes you out to be .... well ...less respected.

:bob you really have a nasty attitude. who died and made you electronics king?
:

4/22/2008 10:21:22 PMEdd








….I just had to let this little feller express my “Shock and Awe” and I’m not even Saddam……’awe I’m not really upset at all …lol.

Mainly, because even you ….Sir Bob …expressed some question yourself,
just a few words later with your:
“It could be that I misread you reply.”


I must now evaluate the misconstrued possibilities:


I am initially seeing that the posting sequences are such that I am only separated from directly linking into your Bob E. Date Time Group 04/21/2008 20:34 post by the Right Honorable kcl’s (two kcl's and one kcj entries...so the kcl's have it ! right ? ) intervening post , thereby possibly , might you assume that I am tying into your post and directing any comments ? towards you ?


NOPE, I just always post at the lowest position, since this post has branched out once above and an added post can certainly be less likely to get overlooked, unless placed in this manner, pending one laboriously looking at all of the DTG’s, and that can not be reliable due to time zone differentials.

Another remote possibility is within the post text, initially, to wit:

"Boy – oh -boooooy what a lot of responses you got .....”MEANING / INFERRED that this thread has certainly GROWN in LEEEEENGTH since I initially stepped in to suggest a cheap-o-solution to the powering situation that I almost exclusively use, plus affording the additional safety of line isolation. ( Later on in the game it may prove beneficial to have an RF RC network tying in from the 120 VAC primary to the 120 VAC secondary.)

"I assume that you finally went with the back to back transformers."

Must be..... since I read later about transformer current values.. the step up to the HV secondary aspect...and only needing in the decade range of current.. it, being discussed with Sir Thomas D.

"Plus the units filaments might have ended up different than I have shown…I like same tube types paired."

I can't see any thing wrong there since I am mainly referring to my schematic which may not have paired up the right two tubes.
BUT shows a set of (2) 6V / 300 ma tubes in series across the full 12VAC supply and the other tube in series with its dropping resistor to make up for the voltage differential.


However, some point in that discussion of the filament hook ups with such short terse throwback and forths, I couldn't tell who was who...maybe I just should have got a program at the ballpark so that I could figure out the players ?

That is why I typically only have my info on a post, along with my distinctive header- tailer to make solid differentiation, in case any one adds onto it....and then their adding on above or below ?


Now all the way down to :
"At one time I checked in and you certainly had a dreadful bed full of circuit errors,"


Just meaning that some schematics...or links to them ...were hard to seek out..just after the one marked with (photo) and then the convoluted manner in which they were laid out and routed, but it eventually led down to the one that I re-plotted.
The only final comment was to try both grid utilizations to confirm the most desirable results.

Lastly on your RF snubbing / bypassing of a SS diode with a ceramic capacitor... I heartily concur.
I was intending to only reinforce what lan is having on hand and is trying to use, and see only a decade or so of current being involved, since there is no 6L6 final tied onto this unit. There will also be a slow cushioned B+ applied to the tubes, with a vacuum tube rectifier being used . If a 4007 was to be used one should also have some cushion on that input filter with a series c/l resistor and ~ 250 VDC rating.

Now, possibly, did I hit upon my SNAFU...somewhere within the above ?



73's de Edd




4/23/2008 10:10:36 PMBob E.
:I just had to let this little feller express my “Shock and Awe” and I’m not even Saddam……’awe I’m not really upset at all …lol.
:
:Mainly, because even you ….Sir Bob …expressed some question yourself,
:just a few words later with your:
: “It could be that I misread you reply.”
:
:
:I must now evaluate the misconstrued possibilities:

:I was intending to only reinforce what lan is having on hand and is trying to use, and see only a decade or so of current being involved, since there is no 6L6 final tied onto this unit. There will also be a slow cushioned B+ applied to the tubes, with a vacuum tube rectifier being used . If a 4007 was to be used one should also have some cushion on that input filter with a series c/l resistor and ~ 250 VDC rating.
:
:
:Now, possibly, did I hit upon my SNAFU...somewhere within the above ?

Nah, don't worry...you're doing fine, better than me actually.

Hey, one has to respect the man after such reply. I do enjoy your post and am glad I did not upset you (you noticed my concern about my reading abilities, i.e. read one's true feelings/intentions from a less than perfect human interface).

Not that you would be totally wrong after reading your complete and thorough technical reply, including a schematic respecting the OP's original project (we're both assuming following the original schematic supplied at the beginning of this thread is best for the OP's interest) and I respect whom can reply to a poster within the scope of his project. How many times have I read, "well....just buy that xxx toy and be done with it", while the OP only needed encouragement to complete a project (self esteem is quite important at all ages). If I were to tell my students, nah don't worry, if you really mess'up, just go to next corner and buy a complete one for 19.95 and be proud of yourself...I'd better leave the profession.

Regards.

4/23/2008 10:33:36 PMBob E.
:...it can only serve to make them feel somewhat intimidated .......

Are you ?

I know I'm not.

In any forum, one can only contribute to the level of his/her knowledge and shouldn't feel diminished when someone of higher knowledge reply, unless done in a condescending manner. I think Edd does a fine job of helping and educating the less technical using a comprehensible language. As a teacher, I sure do appreciate his writing style. Very pedagogic for many I suppose.

I had a kick from his last. while slightly lengthy, reply though.

4/24/2008 12:09:56 AMPeter G. Balazsy
Bob you were simply rude and abrasive..NOT helpful and instructional.
... and that is what I am referring to.
And if you claim to be a "teacher" you must have failed to take those mandatory classes:
"Diplomacy and human behavior" and
"Student Relations and Earned Respect 101"

...Now ..your veiled attempt at elitism is a joke.

and.. lol
....No, I am in no way intimidated in the least.

4/24/2008 6:50:05 AMBob E.
:Bob you were simply rude and abrasive..NOT helpful and instructional.
:... and that is what I am referring to.
:And if you claim to be a "teacher" you must have failed to take those mandatory classes:
:"Diplomacy and human behavior" and
: "Student Relations and Earned Respect 101"

Well, since we're in that period of the day, big hugs, you should look at yourself. You're a prime example of a pedant and condescending poster.

Can't really expect much from a "proud" pizza speaker maker (a 5 yo arts class failure actually).

Why am I not surprised by your continuous cheap shots and snide remarks? Do you feel the grandeur overpowering you by lowering others ? Seems you're pretty good at that, both here and some place else.

Of course, I do not expect any Mea Culpa from someone of your stature. "Veiled attempt at elitism" better describe yourself.

For your information, why do YOU insult me while the person I was discussing with did not find fault ? Oh yeah, the grandeur...Should I call you sir...or Mr. Sir ?

I can't wait for your next facetious remarks. I get to appreciate the short minded people everyday you know, I make a living out of it. But my students usually learn from their errors and become better persons. I don't know about you, probably a lost cause.

4/24/2008 4:27:57 PMIan
I belive this forum is for antique electronics, and this thread for a 2 tube am transmitter.
4/26/2008 12:58:33 AMThomas Dermody
Hi Ian. Sorry this went the way it did. Start a new thread and let us know how you are doing.....and let this thread die.

T.

4/24/2008 6:14:46 PMPeter G. Balazsy
lol
4/23/2008 10:16:01 PMBob E.
:bob you really have a nasty attitude. who died and made you electronics king?

товарищ (tavarishch) kcl, you should definitely comb your hair to the left.

4/24/2008 4:40:31 PMkcl
this is constructive help and the method by which you 'teach'? i fart in your general direction.

:
:Ohm's law is not your strongest point I see.
:
:

4/24/2008 5:21:28 PMRodney King
"Why can't we all just get along?" :-)
4/24/2008 8:47:19 PMJudge Judy
CASE CLOSED,session ended !
4/24/2008 9:27:48 PMO.J. Simpson
I WALKED!!!!

:CASE CLOSED,session ended !



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