distortion ga20

[sdorer]

Friends,
I built a ga20 from an old Hammond organ amp. I'm having a heck of a time with distortion at low volume levels. It uses all octal tubes 6sl7 and 6 sj7. I'm doing a bit of thinking here and I can't figure out why it's happening. Any insight would be appreciated. Also, does anyone know the voltages for this circuit?

[Phil_S]

What are the voltage reading on the 6SJ7 and 6SL7? IMO, the stock circuit has them too low and it kills the headroom.

Here is my take on the GA20 circuit. http://home.comcast.net/~psymonds/GA20.htm and I think it turned out to one really fine amp.

[sdorer]

I followed your schematic and the voltages are in the ball park but everything running a bit too high. The amp does have a better sound and more head room but I'm running the 6v6 platea at 415 volts. I had to modify the power supply as it used to have an old field coil speaker. So I put in a permanent magnet speaker and added a choke. It was still a little high so I added a 1k 10 watt resistor after the choke. I think I need to increase that resistor's value and it should be running fine. Your thoughts? Also thanks for the tip it helped a great deal to increase the voltages.

[Structo]

Yeah, I built an amp from a Hammond A-29 amp.

I had to add a power zener to the PT center tap to bring down the voltages.

Mine uses a 5u4 rectifier.