AFAIC all the designs are good. But this is the one I built: https://www.diyaudio.com/community/threads/6v6-line-preamp.102352/page-209#post-7204481
Same here but different context. I'm thinking of using it as a simple gain stage on the input of an EL84 PP amp. I have limited current available and I'm wondering how low I can go on the 6V6 in triode. Would 4mA work for instance?
Thanks @Bas Horneman ! It looks a little different. Some more year of experimentation evidently! Good it has a little feedback applied. Any change on the power area and filtering? Transformer is always 350-0-350? (i'm gonna order one, or use a 370 i jave, but this one is a big one, more for a power stage... 280ma. I think 100-120ma would be enough for 2 6V6.... )
I just found my old chassis with sockets, cabling and potentiometers already mounted, ready to be finished... after 13 years? (more or less... il will have to check the first posts, i remeber it was christmass 2011 or 12 when i made the chassis). Any improvement on microphonic?
I just found my old chassis with sockets, cabling and potentiometers already mounted, ready to be finished... after 13 years? (more or less... il will have to check the first posts, i remeber it was christmass 2011 or 12 when i made the chassis). Any improvement on microphonic?
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Ever tried a 6V6 SE amp? < than 3w, but incredibly loud and sounding really great. Triode strapped. 2 6J5 and 2 6V6 . That is way i want to finish the 6V6 preamp--- it would be nice to have a complete amplification based on this incredible tetrode.
Transformer secondaries voltage spec depends on what PSU style you have in mind. Vacuum or solid rectified, passively or actively filtered, how many filter stages, what are the voltage losses, etc.
You finally look for about 330V rail on the running preamp. It must be a quiet rail. Two 6V6 bottles in this circuit will pull about 40mA total for bias.
Those are the only standards.
Duncan's free PSU simulator should also help you model your architecture.
You finally look for about 330V rail on the running preamp. It must be a quiet rail. Two 6V6 bottles in this circuit will pull about 40mA total for bias.
Those are the only standards.
Duncan's free PSU simulator should also help you model your architecture.
Thanks @Salas ! Ill go for a gz34 or 5au4, i have plenty of those, but they are a little bit excessive for the current needed... i have some 6x4 6,3v and other 5x3 and 5y3 (i'm on a train, cant check until tomorrow night) but i prefer indirect rectifiers, to save tubes and capacitors.
I cant use Duncan simulator. It only works on windows and we are all on Linux... but i will try to install a symulator to see if it works. Either its all hard math, and i'm getting too old for it. I though to go with capacitive load, CRCLC. There i split left and right and go RCLC. I love the separation that gives the splitting. I normally prefer inductive load, with a 20-30H chocke first, but the transformer would get much bigger to get the extra voltage needed.
So probably i will have to go for a 300 or 320-0-320 AC if i understood well or even 350 tohave more margin
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andyjevans,
Salas,
It is good to see more new ideas.
6V6 screen used 'as a plate'.
That sounds like a good idea, using it as a low mu (u), low power triode input tube, or driver tube.
Long ago, I designed and built a 4-65A Tetrode amplifier with the Plate Grounded, and the Screen used as a Plate (10 Watts max screen dissipation).
The 4-65A has a birdcage grid, and a birdcage screen. Those birdcages have the same number of wires, and are aligned to create "Beams" (sheets) of electrons. The plate is also circular.
It is a very pretty tube, with thoriated filament.
I consider it to be a linear tube (Tetrode kink when used as a Tetrode; but linear with the screen uses as a plate, when the plate is grounded).
Unfortunately, I only had about 350V to run the screen, and 5k primary output transformer.
I needed 600V to run the screen, and a 10k or 12k primary.
Have fun using a 6V6 Screen as a triode plate, and 4mA of current.
Please let us know the results if you try it.
Salas,
It is good to see more new ideas.
6V6 screen used 'as a plate'.
That sounds like a good idea, using it as a low mu (u), low power triode input tube, or driver tube.
Long ago, I designed and built a 4-65A Tetrode amplifier with the Plate Grounded, and the Screen used as a Plate (10 Watts max screen dissipation).
The 4-65A has a birdcage grid, and a birdcage screen. Those birdcages have the same number of wires, and are aligned to create "Beams" (sheets) of electrons. The plate is also circular.
It is a very pretty tube, with thoriated filament.
I consider it to be a linear tube (Tetrode kink when used as a Tetrode; but linear with the screen uses as a plate, when the plate is grounded).
Unfortunately, I only had about 350V to run the screen, and 5k primary output transformer.
I needed 600V to run the screen, and a 10k or 12k primary.
Have fun using a 6V6 Screen as a triode plate, and 4mA of current.
Please let us know the results if you try it.
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I've never tried that. How do you get the operating conditions and curves and max. dissipation?
andyjevans,
6V6:
The screen is rated for 2 watts dissipation.
g2 to g1 mu (u) is about 8 or 9.
Start with 250V on the screen, and 15V bias.
Try a 3900 Ohm self bias resistor, and see what current you get. 4mA would be 15.6V self bias.
Just a place to start, and adjust from there.
But you probably do not have 350V B+, to get 100V across a plate load resistor.
So . . .
Or, to get close to a real world circuit, 250V B+, a 30k plate load, and a 1500 Ohm self bias resistor, should get you close to VP 125V, and 3 to 7 mA.
You Can't hurt the screen with these starting resistor values, it will be far less than 1 watt screen dissipation.
I feel like I am at a high school basketball game, the cheerleaders are shouting: Ground that Plate! Ground that Plate!
I edited my Post # 4909, before you wrote your post # 4910.
You might want to re-read my Post # 4909.
Have Fun!
6V6:
The screen is rated for 2 watts dissipation.
g2 to g1 mu (u) is about 8 or 9.
Start with 250V on the screen, and 15V bias.
Try a 3900 Ohm self bias resistor, and see what current you get. 4mA would be 15.6V self bias.
Just a place to start, and adjust from there.
But you probably do not have 350V B+, to get 100V across a plate load resistor.
So . . .
Or, to get close to a real world circuit, 250V B+, a 30k plate load, and a 1500 Ohm self bias resistor, should get you close to VP 125V, and 3 to 7 mA.
You Can't hurt the screen with these starting resistor values, it will be far less than 1 watt screen dissipation.
I feel like I am at a high school basketball game, the cheerleaders are shouting: Ground that Plate! Ground that Plate!
I edited my Post # 4909, before you wrote your post # 4910.
You might want to re-read my Post # 4909.
Have Fun!
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*
Of course you don't want to drive a low impedance power amp from a screen output preamp. Zout is high. You got to lose some kind of ability when running at 300mW. But many tube power amps are/can be high Zin 100kΩ or so, hence interfacing is not always a problem. Low capacitance output interconnect cables are also preferable.
Of course you don't want to drive a low impedance power amp from a screen output preamp. Zout is high. You got to lose some kind of ability when running at 300mW. But many tube power amps are/can be high Zin 100kΩ or so, hence interfacing is not always a problem. Low capacitance output interconnect cables are also preferable.
Salas,
and
andyjevans,
I estimate the screen impedance, rs, to be Less than 5k Ohms at 4mA screen current (with the plate Grounded).
That is about 1/2 of a 12AT7 plate impedance, rp.
That is about 50% less than a 12AU7 or 6SN7 plate impedance, rp.
Etc.
That is plenty low enough screen impedance, rs, to drive the input stages of many vacuum tube power amplifiers.
Build the preamp. Capacitor couple it from the screen to the output, start with a 1 Meg Ohm to ground at the output of the capacitor. Wait until the coupling cap charges.
Put a small signal into g1.
Measure the plate signal voltage out.
Connect a 5k resistor to ground in parallel with the 1 Meg resistor.
Measure the plate signal voltage again, if the voltage is 50% or more of the first voltage reading, the output impedance is 5k Ohms or less.
Done.
Try it and see.
Please let us know.
Just my opinions.
and
andyjevans,
I estimate the screen impedance, rs, to be Less than 5k Ohms at 4mA screen current (with the plate Grounded).
That is about 1/2 of a 12AT7 plate impedance, rp.
That is about 50% less than a 12AU7 or 6SN7 plate impedance, rp.
Etc.
That is plenty low enough screen impedance, rs, to drive the input stages of many vacuum tube power amplifiers.
Build the preamp. Capacitor couple it from the screen to the output, start with a 1 Meg Ohm to ground at the output of the capacitor. Wait until the coupling cap charges.
Put a small signal into g1.
Measure the plate signal voltage out.
Connect a 5k resistor to ground in parallel with the 1 Meg resistor.
Measure the plate signal voltage again, if the voltage is 50% or more of the first voltage reading, the output impedance is 5k Ohms or less.
Done.
Try it and see.
Please let us know.
Just my opinions.
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It should be about 10k Zo in my example. Because I have already tried that procedure in LT Spice. Maybe lower if the cathode resistor is bypassed. In exchange of more gain, and higher THD most probably. More than three times (9-10dB) voltage gain is impractical for line level control when using modern source equipment in my experience.
Salas, one short question. I came in exchange for two NOS paired Russian 6P6S, I have one HV power supply 250V (CRC then TL783C) from other project which should be slightly adjusted for a higher voltage, I have a transformer 80VA with a secondaries 250VAC and 12.6VAC. Can I use it to make your preamplifier or even better a buffer? I guess the HV would be around 280-300V in this case, so I would modify the resistors in the circuit a bit, or leave it as it is. Can I wire the heaters in series to use the 12.6VAC heating, or does the heating have to be DC?
Which common cathode version, the G3X? Heaters can work in various schemes when you need to. AC and series ain't the best for performance and flexibility when you have a choice but it will function. Only check that the certain tubes do share the heating voltage almost equally. Heat them on a breadboard test or something.
G3X is the feedback version. https://www.diyaudio.com/community/threads/6v6-line-preamp.102352/page-209#post-7204481
Thanks. I used this type of NFB very successfully on the AIKIDO preamp (50k+150k = gain 2,5x).
It will be a cathode follower with 6P6S/6V6GT. With this DAC and amplifier, I don't need voltage amplification. Just a buffer for potentiometer.
I just don't have experience with AC heating, it should work fine with CF. If there is some small imbalance on the two heaters, I don't believe it will have much effect on performance.
It will be a cathode follower with 6P6S/6V6GT. With this DAC and amplifier, I don't need voltage amplification. Just a buffer for potentiometer.
I just don't have experience with AC heating, it should work fine with CF. If there is some small imbalance on the two heaters, I don't believe it will have much effect on performance.
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