1974 Marshall 2204 Lee Jackson modded gut shots

[Markedman]

This is a link to my Flickr account showing the insides of my amp. It has plenty of gain but it sounds muffled and isn't very tight in the low end. The loop sucks, basically unusable the way it is. I hooked my Boogie preamp up to the return and it sounded awesome, not muffled. Of course I've changed tubes and speaker cabinets to no avail. I'm looking for a tech who wants to take this amp in and upgrade it for me.

1974 Marshall Lee Jackson gut shots by John Bazzano, on Flickr

 

[SpiderWars]

That thing is a mess but the board itself doesn't look too butchered. I didn't really notice in the clip, how noisy is it? And what is wrong with the loop?

And I don't know if you knew it or pulled it but that MV on the back looks to be a pull-pot to take it out of circuit. Does that MV even work worth a damn? It is post-PI but not the typical LarMar type that uses a dual-ganged pot. Looks almost like a cross-phase type which usually doesn't work well in an amp with NFB (because it is inside the loop).

 

[glip22]

I think it could be tweaked easily enough. Change the first stage bypass cap and resistor to 2k7 .68uf. Drop the PI output put coupling caps to .022. That should clean up your mud.

 

[Markedman]

Not noisy at all. The loop sounds grainy no matter how I set the knobs and when I turn it off, push the return knob in, it sounds much louder and clearer. The master in the back works well, it is a pull out. When I crank it, the amp sounds fairly stock with the gain and front master set low. I will take a video going over everything and post it. Thank you for your response.

All in all, if the amp was just clearer and the low end tightened up, it would rule.

 

[SpiderWars]

Did you try plugging a good short cable from Send to Return? If the Send jack shorting is flaky it can cause issues.

 

[Markedman]

Did you try plugging a good short cable from Send to Return? If the Send jack shorting is flaky it can cause issues.

I just tried that. No difference, thanks.

I think it could be tweaked easily enough. Change the first stage bypass cap and resistor to 2k7 .68uf. Drop the PI output put coupling caps to .022. That should clean up your mud.

Thank you, the amp is close to sounding great, I'll see if I can find a local, NYC/Boston, tech.

 

[Racerxrated]

I've had 2 of these and they are really nice sounding modded Marshalls; they stay very true to the original tone if that makes sense. Try cleaning the loop inserts with deoxit; that might help. In fact take deoxit and clean ALL the pots, and tube inserts. I had a Cameron Ocean MiG 100 that didn't sound healthy at all, turned out the gain pots were VERY dirty and deoxit worked perfectly.

 

[Markedman]

I did it this afternoon, thanks for the advice. It's worked well in the past.