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Topics - pinkjimiphoton

i picked up the pcb for a marshall 5010 a couple years ago on ebay.
its the two horizontal input, one headphone/line out, full tone stack with presence 30 watters.
the bottom of the pcb is marked jm78-2
it works, i hooked it up to test it and am gonna get a proper hammond transformer for it and roll my own little beast out of it hopefully, but its a little different from any schematics i've managed to find. seems like there's 3-4 different versions of the amp, but i can't seem to find any really helpful info with google, which seems to have covid brain these days .
if someone could help me out, i'd be grateful! thanks!
Amplifier Discussion / marshall 5212 channel bleed fix?
February 18, 2020, 05:01:03 PM
hi folks,
restoring two of these that i picked up. replaced all the electros and tants, and they are now nice and solid and dependable... so far ;)
but i get a bit of channel bleed happening from the dirt "channel" into the "clean" channel when i have the gain pegged on it, even with a proper footswitch hooked up. the clean channel sounds great only if i turn the dirt gain to zero.
been messing with pedals and amps for years, but never really dealt with this kind of situation for the switching before, and not really sure how/where to look, or if there may be a modification i need to make possibly... maybe add a snubber to ground somewhere or something?
here's the schematic

also, another question. it seems to me marshall dropped the ball on the design in one crucial way...
its not really two "channels" like in, say, a fender amp or something, looks more like its just switching gain stages? or am i as confused as i think? ;)

the problem is that the clean volume is affected by the master volume. the gain channel has gain and volume, both of which sound best cranked. it appears they figured  you'd crank the dirt gain, lower the dirt volume and then set the master for both channels.. but it sounds better with the gain and volume cranked, and the master lowered.
BUT then the "clean channel" gets overdriven and sounds bad... like a silverface 70's master volume that doesn't belong on any fender.

is there a q&d mod that could be made to take the output of the clean channel volume right from the wiper and dump it just post the master volume instead? that way, the master could be used to really dial in the distortion, and the clean, well, ya just turn it up, it doesn't really NEED a master volume imho.

thinking breaking the node at r10 and r9 and ic1a pin 2, and instead connecting the freed side of r10 to the node at r27 and the fx send jack?

would love advice opinions and guidance if anyone can spare a few minutes to take a look
Amplifier Discussion / Marshall 5203 220-117v mod?
February 03, 2020, 09:00:05 PM
hi peeps,
long time lurker, first post i think...
i have one of these amps

i'm hoping to pick up, but just realized its a canadian model set up for 220v, and i live in the usa where its 117v
(give or take)... looking at the schematic, it looks like i should be able to just move a couple wires on the power transformer to choose, and maybe change the fuse value to a slightly higher one..
but not sure looking at it, which way would this be implemented?
sorry if a dumb question, but it looks kinda like they jumper two parts of the power transformer together... would i just use one half of the pt primary? or do i need to remove something?
i'm a fair hand with a fuzzbox, but this is pretty much my first real rodeo with this kind of thing so i appreciate any advice i can get. thanks so much!