Wiring pins 12A*7 to (2) 6AV6

[Claudiog]

I'm trying to work on a project of replacing 1 12AX7 that's works with 12V, and using 2 6AV6 that works with 6 volts. I have some issues with pinout using data sheet I figured that way.

12A*7 = 6AV6
  1      =    7
  2      =    1
  3      =    2
  4      =    3
  5      =    4

6AV6 is half of 12AX7 so I will need a to re conect pins 6, 7 and 8 to new 6AV6 pin 7, 1 and 2.

can someone light me up¡?

[Travis]

I am not understanding exactly what your question is.

If you’re wondering how to power the heaters off 12V you could wire them in series so each gets 6V assuming there is sufficient current

[Claudiog]

I'm trying to replace one 12AX7 with two 6AV6, and Im a little confuse since 6AV6 pin 5 and 6 sholud conect both to gorund, and works with 6.3volts, I will work with that voltage, but I need to know exactly pinout to replace them.
I would lilke to buid something like a valvecaster but using 2 of this little 6.3v

[Travis]

Are you referring to AC or DC? Are you referring to the heater voltage, plate voltage, or both?

12ax7 pins on the left 6av6 on the right

1 = 7 plate
2 = 1 grid
3 = 2 cathode
4, 5 = 3, 4 heater

Pins 5 and 6 of the 6av6 are diodes

6av6 wants 6.3V for the heater but will perform better with a higher plate voltage

[Claudiog]

The main idea is using DC and refering to both, so I guess my pinouot reference is ok.

I was thinking in 6.3 voltage to pin 7 with 220K and 6.3v to pin 4, and ground to pin 5, input signal to pin 1, control gain pot to pin 2, and output from pin 7 after capacitor. and then repeat to another 6AV6.

thats the general idea look, not the final values, probably use dual gain pot for both pin 2 (not in the picture) and same R for both pin 7:

[Travis]

Looks good. Let me know how it sounds with that low voltage on the plates

6av6 is nice and cheap. Sounds like a cool project

[Claudiog]

I'm in drwaing schematic part, I will post results, questions and burns

Do you think is ok for first try diagram? I will adjust values based on info and test.

Thanks Travis!

[Travis]

Yeah I think your schematic looks great. The only thing I’m not sure about is whether you should leave pins 5 and 6 unconnected or ground them.

I need to find more information about this before I can offer specific advice on pins 5 and 6. My gut tells me probably leave them unconnected but I need to do some more research and get back to you

[Claudiog]

On the way of searching I found that some schematics says tied both 5 and 6 to ground and somes are floating. So first try is left them unconnected.

[Claudiog]

1st attempt I lost one 6AV6 and that's a pain, I took for granted that I have 2 of them out there, so my first try was only with one 6AV6, no gain at all, a little dark boost with low volumen and no gain, almost completed clean, using this values
C1 47nf
R1 1M
VR 50k
R2 220K
C2 is output 1 uf
tone 10nf and 100K pot, and vol 100K,
6.3volts, pin 5 & 6 grounded

I have a couple of 6av6 in a old amp I will try to fix some values around R2 and gain pot and then complete the original schem with 2 6AV6.

[Claudiog]

Can I go safe to load 9v DC on 6av6 plate? Seems we need more power here. The heater with 6.3 looks good but I guess I need to increase plate voltage

[Travis]

Yes. Under normal circumstances the plate voltage would be much higher. The max voltage rating for the 6av6 plate is 300V.

With a low plate voltage the tube gives you reduced gain, headroom, and bandwidth. This is done in the valvecaster design so that the pedal will behave like an overdrive and also obviously because it is cheap and easy to avoid the high voltage power supply.

[Claudiog]

second day:

changes:
R2 470K feeded with 9v DC,
gain pot 500K

results: a little more headroom and volume, and a little gain added, not an overdrive yet, better than first try, it takes two minutes to feel the valve gain

[Claudiog]

3rd day:

Well I found and old man that provided me the missing valve and a couple of 12av6 the same as 6av6 but with 12v on heaters
Changes from the original diagram:
R1 is 2.2M
R2 an R3 470K
R4 is 1M

Gain pot for both valves are 1MB and I feel that I will Change to Log.


Well the first try with all the changes on the components and with 2 valves sucked, low gain, low volume, and lot of noise with a regulated 9V filtered and then a regulator to 6V.
I put a 12V power supply not filtered and a regulator for 6 volts and hell the change was amazing, a lot of volume, more gain, very articulate, and no hum, is a low gain overdrive that cranks really well, and my thumbs are burned because regulator from 12v o 6v is very very hot.
I will try more changes but 12av6 with 12 on plate and heater sucks too, probably need higher voltage for plate.

[Travis]

That’s awesome!

Regarding the voltage regulator, what model are you using? The two 6AV6 heaters should draw about 600mA together. The 12AV6 heater current draw is actually half that so if you get them sounding better that might be a good reason to use them

Usually with voltage regulators it is recommended to feed at least 3V higher than the regulated output voltage. A heat sink may be necessary on the regulator

[Claudiog]

I will need to check mA from power supply I guess is around 500mA. I put a heatsink but it's too hot yet.
Actually Im using LM7806 but maybe put first Lm7809 and then 7806. I need to experiment.
I guess 12av6 needs more plate  voltage with 12v and 12v for heater sounds very bad.  I have 18AC but the original idea is using DC.
I will dig for a bigger mA power supply.

[Claudiog]

Day 4:

Bad day, after a couple of changes the the vero board failed, so I have to re do, (is easy to do on protoboard, but i'm lazy).

Day 5:

New board, a few changes. I removed complete the gain pot and pot 100R to ground and then a 10uF parallel to that R. thats the same for second valve to pin 2.
Moved the gain pot to R4, is better to control gain overall , I used a 500K lin.
I made a charge pump, so finally is much much better, I run 12v with 7806 with heatsink that gives me 6.0v for both heaters, and charge pump gave me 23.5v for plates.
almost double of headroom and double volume output, is fucking loud, gain increases but still on max gain is a nice overdrive sound not even close to high gain at least with this 2 6AV6 General Electric.

Next day more testing about caps, and probably test 12AV6 changing heater voltage