Ugly distortion with tube amp when you play

[TigerAmps]

Also, measure the current with signal - does it have a little or no fluctuation or a large swing in current ?

[Ampzone]

Yes EL34 should have 6.3 on the heaters - not sure if they would even glow at 3.15 Volts ...

It's a total of 6.3v across but 3.15 on each single pin 2 or 7.

[Ampzone]

Wait. You measured (as opposed to calculated) the 32-35ma per tube, right?

The tube draw on all the output tubes range from 32-35mv

[Ampzone]

Also, measure the current with signal - does it have a little or no fluctuation or a large swing in current ?

Are you talking about the input grid negative voltage amount or what the mv amount is on each tube? As I mentioned above they are running between 32-35mv so the bias looks normal to me considering the plate voltage appx 460v.

[g1]

He's talking about that mV figure per tube.

[TigerAmps]

That looks OK for idle; what about when you apply signal and turn up the volume - how large is the current fluctuation?
I use a bias probe to get a feel for what is going on ....
Also, can you swap out the OT for a known good one, just to rule out the OT

[Mickey]

Interesting circuit as it deploys two cathode follower stages. Have you checked that the correct tubes are in place, the phase splitter is a lower gain ECC81. I would check the voltagess working back from the output tubes, check the bias voltage to these tubes and that the control grids each have the same amount of bias supplied. If these measurements appear normal then go the phase splitter and check the anode voltages which again should be equal. If all voltages appear OK then the trouble shooting becomes a bit tricky.
A CRO is a great tool but unless you understand it's short comings and also have a calibrated/adjustable low distortion audio signal generator it may not provide any real answers at this stage in your trouble shooting. A 10mV signal at 1Khz would be required to utilize a CRO, first set to a sine wave signal and then set to a square wave signal, but I'm getting ahead of myself.
Good luck and keep us posted. Mickey

[Ampzone]

He's talking about that mV figure per tube.

I just have bias readings and the negative voltage

[Ampzone]

29mv, 32mv,30mv and 34mv

[The Dude]

This helps, so far the wave looks normal around V1 after that around V2 it starts to look jagged or hacked off so to speak around the 220pf cap around the treble pot. It is not longer an even sine wave. Now maybe this is normal? for this type amp. Now with the audio probe plugged into an external amp I get signal all the way to the grid stoppers on V5-8 pin 5 input. The sound is the 1k tone and not unlike the earlier stages.

Is it possible you could post pictures/scope shots of what you are seeing? What you describe seems like a potential issue to me. IMO, although I'm not saying an audio probe doesn't have its uses, a 1K tone can be pretty distorted before your ears actually pick up on it. I'd much more trust a visual representation of what's going on.

[Ampzone]

Is it possible you could post pictures/scope shots of what you are seeing? What you describe seems like a potential issue to me. IMO, although I'm not saying an audio probe doesn't have its uses, a 1K tone can be pretty distorted before your ears actually pick up on it. I'd much more trust a visual representation of what's going on.

I will try and get some shots in the AM. The tubes are set to the right arrangement. I have a 50w ot I could try to rule out a bad ot, but I am not sure that is ok.

The primary readings on the OT are under 20ohms, that I can say and the primary to ground is in the high MEGs.

[Ampzone]

I will see what the bias spikes up to when I play in the AM.

[J M Fahey]

Whatever you measure while playing is not "bias".

In fact, bias *should* properly be called "idle bias".

[Ampzone]

Whatever you measure while playing is not "bias".

In fact, bias *should* properly be called "idle bias".

good to know

[Ampzone]

100hz tone.
Starting first pic is the input jack 1meg & 68k intersection, next input jack 68k&68k intersection, next 68k and input volume pot, v2 pin 6, 220pf cap. Not sure if this helps at all.

and treble pot and 220pf cap intersection.