Marshall JCM 900 100 Watt Master Volume

let's take a look at this hybrid amp from recent times, as opposed to a beat up plexi,

sucker cuts out after 20 minutes of hard core, 

looking at it while chanting some zen mantra did not fix it,

so we need to get under the hood for a looksie,

nice layout and wiring,

plenty of those plastic jacks we love so much, 

tubes have those cool Marshall retainer thingy type deals,

impedance switch is n ot the best thing on the back panel,

we like hard wired steel jacks that say  4 ohms, 8 ohms,
but since this amp gets used with two cabs, the switch can make life easier,

mains wiring

bias pot could be bigger, that three legged sw is the spk Z switch,

boards sit under the tubes which means no baking the G10 while you play, 

preamp board has opamps on it, this amp still gets good crunch even with the solid state front end,

so what was the problem?

we beat on the boards with chop sticks, resoldered both boards, put a heat gun on it, dang thing still had problems, trouble was getting the sound level to drop long enough to trouble shoot it, so we put on some ear goggles and hammered it on  11 for five minuets, and like magic, it cut out, long enough to pin point the trouble,

it was this guy>
(notice the cheese ball feedback resistors sitting there waiting to break, only bad part of the build)

it was that dang Dagnall OPT,

this means we have to take it apart to rewind, gosh darn it,    ;D

hope you don't have the same batch number on yours,

see transformer thread for further info,