Gibson GA-30 with 12ax7 preamp. Harsh Distortion. Sawtooth waveform.

[Pinball]

Trying to service a 60's GA-30. This particular amp has V1 and V2 as 12ax7. V3 is a 12au7 (Phase Inverter)

I don't like the harshness of the gain. When I put a nice sinewave in at the input, I am seeing a very sharp almost sawtooth at the output of v2b when I add any volume over 25% of the vol pot. All the tubes are good.

This circuit has the "tone expander" as well.  NFB off the output transformer.

If I turn the tone pot down almost all the way, I lose gain, but the output waveform starts looking more like a sinewave again.

Do you think the issue is in the tone circuit?

[pdf64]

Trying to service a 60's GA-30. This particular amp has V1 and V2 as 12ax7. V3 is a 12au7 (Phase Inverter)

I don't like the harshness of the gain.

My guess is that's due to a positive feedback loop forming via the shared V3 cathodes.
Fully bypassing it might help with that.

When I put a nice sinewave in at the input,

Amplitude and frequency?

I am seeing a very sharp almost sawtooth at the output of v2b when I add any volume over 25% of the vol pot.

Just to note that 25% on a linear pot is well over halfway on an audio taper pot.

This circuit has the "tone expander" as well.  NFB off the output transformer.

It looks like a bass boost?

If I turn the tone pot down almost all the way

It's another linear track, all the change happens between 0-33% rotation.

I lose gain, but the output waveform starts looking more like a sinewave again.

With the volume settings you're using, the tone control is causing a treble boost unless it's turned pretty low, eg 10% rotation.

Do you think the issue is in the tone circuit?

I suspect the issue is with the paraphase splitter.
Or just old ecsps 

[shooter]

Do you think the issue is in the tone circuit?

I suspect the issue is with the paraphase splitter.

did you probe "inside the TS"??
sometimes you get pretty ugly stuff from scope loading/impedance


I typically test a TS to the "left" of the "input coupling cap" then the plate of the recovery tube, if those are "close to normal" move on down the stream....

[Pinball]

Turns out it was the 220k resistors prior to the phase inverter. One was open and the other was reading extremely high. In total there was 8 resistors that were way out of tolerance. I replaced all of those. One note, I changed V1 to a 12at7. That actually made the amp much more usable. No clean headroom after 2,3 on the volume until I did that.

[pdf64]

Turns out it was the 220k resistors prior to the phase inverter. One was open and the other was reading extremely high. In total there was 8 resistors that were way out of tolerance. I replaced all of those. One note, I changed V1 to a 12at7. That actually made the amp much more usable. No clean headroom after 2,3 on the volume until I did that.

Well done!
So the overdriven tone is ok now?
The only 220k I can see on the post 1 schematic are the V3 anode load resistors?
I suggest you consider fitting volume and tone controls with a decent audio taper, eg Alpha Taiwan.