Although this site is mostly dedicated to my own original circuits and builds, I've originally envisioned it as something wider, to collect my other electronics experiences too.
To start with that, here's my circuit trace of an old Italian amplifier of which I received only the chassis. I could find available schematics online, so here it is to share for analysis and repair purposes.
Even if there are some curious things going on and I can't assure the trace is 100% accurate, I did triple check the weirdest sections and I feel quite confident about it.
Things to notice:
The low-impedance input stage has a twin-T feedback filter that boosts the high mids. This is an attempt to bring back the resonant peak of the guitar lost with the low impedance.
The unused input is shunted to ground. The filter that creates is surprisingly inoffensive, given the virtual ground nature of the input amplifier.
The tremolo, differently from many old amps, shunts the signal right at the input with a BJT used as VCR. This works for both channels and might be an attempt to make it less taxing on the high impedance source on the "Hi" input.