Polytone Mini Brute Power Amp Distortion / replacement reverb code?

[smilan]

Hi, I need help troubleshooting this power amp. The output is distorted on the top portion of the waveform. I have a scope and a signal generator. Where I should look fist?
This amp have been worked by other technician before and Q1 seems to be different from the schematic (C1583 instead of 2N2510).
Also the input transducer of the reverb tank is faulty, what is the right Mod / Accutronics replacement reverb code?

Scope view:

[Jon Snell]

That is crossover distortion.
Ensure you adjust the bias voltage to give between 2 to 3 mV across R17.
No load, No signal.

[g1]

The tank was probably the 1DB2C1C which was used in several of the small Polytones. A more common one that should work fine is the 8DB2C1C.