'89 2204 combo originality / any modifications?

[LPman]

I purchised this '89 Marshall 2204 1x12 combo (4010) today. On paper it only differs from the head by an added cap to the mid pot (C13), otherwise exactly the same.

The cosmetic condition of the amp is like new, totally mint overall. Do you see any replaced parts or modifications on the chassis?

After turning off the amp one power tube seems to be a little hotter to the touch than the other, what could be the reason? No red glow while playing loud, no noise or anything.

Can I snip one leg of that extra orange cap to remove it from the circuit and make it exactly like the 2204 head?

BTW: the stock G12M-70 is truly the absolute worst Celestion speaker I've ever heard. I just put in a Chinese V30 temporarily and the amp already sounds light years better (and I'm not a fan of V30s either).

 

[Purgasound]

I agree, the G12M-70 is awful. I've got a couple cabs with those and they sound terrible. No life, no presence, no fun.

The circuit looks stock although someone did change R30 and the two bias smoothing capacitors. As long as it's a 10uF cab with at least a 100V rating it should be ok. I would change them out for axial leads though. R30 was changed to give the amp more or less bias range. If one tube feels like it's operating at a different temperature than the other than they may not be matched. Only way to tell is to take a bias measurement. I would use two probes and watch them both at idle. If you don't mind using a soldering iron you can place a 1 ohm resistor in between pins 1 and 8 on the power tube sockets and you can read the negative voltage across the resistor. That's the way I prefer to do it in old Marshall amps. Makes biasing easy without fooling with probes.

 

[LPman]

Thanks for the reply! Maybe the previous owner experimented with 6550 tubes which the US market 2204 versions came stock with?

It currently has Russian Svetlana EL 34 tubes (they seem old) but not the Winged-C variety.

I have to get used to the sound and feel of the amp. Much different compared to my 69 JMP 50 even though it's also set up as a 2204 right now. On the same cab the combo is louder when cranked (much higher plate voltage I suppose), has less gain, feels stiffer and the pots must have a different taper because the EQ is very different if I use my usual setup.