Thought this particular amp was an original untouched circuit, but discovered it had been slightly "adulterated"
What I found:
1. V1b cathode: the stock 2K2 resistor (in parallel w/ 47n cap) lowered to 1K5
2. V2a: A 1uf bypass cap added to the cathode (there was not a stock 47n bypass cap)
3. the 220pf cap in the tone stack (off of the treble pot leg) changed to a 1000pf.
The amp sounds really good, but a bit too bright. I don't mind the extra gain and clarity that I'm assuming is afforded by the lower value resistor on the input and the cathode bypass cap on V2a. I'm thinking the excess brightness might be caused in combination by the changed cap value in the tone stack and the cathode bypass cap on V2A.
So I'm planning on working backwards reversing the mods and start by putting the 220pf back in the tone stack.
So my question....Since the amp has already been messed with, are the any other bypass cap values (or input resistor) anyone might recommend trying?
Also while in here, I'm replacing the power supply electrolytics. Found the correct value cap cans thru ARS.
Any thoughts or suggestions will be most appreciated! I know Marshall's very well in terms of dialing in tone by minor circuit changes, but am new to Hiwatt's in that regard. For the most part, I'm a "if it ain't broke, don't fix it" guy and usually prefer just leaving them as is, so I am not opposed to simply returning this circuit back to completely stock values.