I have problem with tube amp Orange OR120.
Got it in non working condition, power section is refubished, all ok.
There are only 2 tubes on output, two of them are pulled off, impedance is set appropriately, one level lower.
Amp starts hard clipping (neg.side only) at low input.
Inverter (12ax7) is concertina/cathodyne, known as may be problematic.
Schematic is from early 70', as is seen on the photo.

Anyone with idea where to start?
It looks like too low bias in inverter?

Resistors and caps around inverter and power tubes are new.
Output tubes are new Tad EL34, running at 500vdc at plates, bias is set to 27ma.

Here is scope screen and schematics:

Hi guys (and girls?), new member here.
I found this forum very helpfull with polite debate and full of usefull information.
Therefore I'm kindly asking for some help with SS guitar amp.
I try to repair tube amps from time to time, ... this time I have SS amp on the bench.

It is about Fender Roc Pro 700.
Problem is, amp is clipping/cutting off, or farting, on stronger attack.
So, at low volume it sounds nice as it should, but if you turn volume a bit higher and hit the chord it sounds like blocking distortion.
It seems it goes to full conduction (short DC pulses) at peaks only.
It is related to clean and drive channel, but in clean is clearly noticeable.
If I hook guitar (vintage strat) into Return of FXloop I get same problem, less noticeable as this input is less sensitive.
Guitar output is max around 100mVAC (volume and tone stack full open).
If you hit the chord hard, I may turn up volume in clean channel to max 2-3 without hard clipping on peaks.
Measuring signal (scope) at Send output, signal is not clipped.
Also output of driver chip MC1436 (pin 7) is clean, problem is in power amp (TIP142/147), I think.

Testing with tone generator&scope clean/normal channel:
Input singen: 40mVac (volume max)
Output dummy load 8,2ohm: 22,7Vac before clipping
Input singen: 190mVac (volume half)
Output dummy load 8,2ohm: 22,8Vac before clipping

Testing with tone generator&scope on Return input:
Input singen: 140mVac (att.=-7dB)
Output dummy load 8,2ohm: 22,5Vac before clipping

I did change electrolityc caps, all of them.
All solder joints were inspected and mostly re-soldered and clean.
Heatsink and transistors (TIP142/147) were cleaned and fastened with thermal paste.
Power supply DC voltages are all OK, as per schematic
(+42,6Vdc/-42,2Vdc; -17,60Vdc/+17,36Vdc)
DC on output (+/-), no loudspeaker, is around 2mV.
Output transistors are getting warm with no signal on input, but not hot, after 15min.
Voltage across emitter resistors 0,47ohm/5W = around 48mVdc each (100mA), no signal, no load
Bias, emitter-base TIP142=1085mV; TIP147=1113mV; no load, no input
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Any thoughts regarding biasing output transistors?
Probably, if you look at scope photo, it is kind of oscillation problem?
Photos:
*sin wave after begining of clipping
*square wave before clipping

Also, when you hook a scope to such output – where to put ground of scope?
Minus of speaker is not at the same potential as ground!
(Photos are made without ground of scope connected, otherwise amp oscillate)