due to the presence of the "rock and roll" switch, im going to assume set b....


sadly however, at the moment the rock and roll switch seems to neither rock nor roll, just mess with the effects a bit and make the humming louder.......

thanks for the input

im not entirely sure whether its set a or set b just yet......its kind of hard to compare it to the schematics.....with the way this thing is put together you have to take half of the chassis apart to get to anything. first there are three vertical pieces of sheet metal, one that comprises the front with the preamp and effect boards mounted to it, then one after that seperating the preamp section from the power section, and then one making up the back with two big heat sinks and the speaker jacks mounted to it. all of the transformers and can caps are mounted on a horizontal piece situated between the divider and the back, along with the power amp board mounted vertically through a slit in this piece with a couple of L brackets. then hold the whole mess is held together with some end caps and sheet metal screws. ive never seen anything else like it.......

another thing that drives me crazy is that the part numbers for some of the transistors on the schematics dont match the part numbers on the parts list (although i am figuring it out, it just takes longer...)


anyway, my next step is going to be replacing the electrolytics, like you said, theyll cause problems eventually, and if i know theyre all good i can rule them out as a problem. being as this is a 45 year old amp and probably hasnt been used in years im sure theyre pretty dried out. the tough part is going to be finding some 4500uf 50v caps that dont cost an arm and a leg.....

so i got this amp at a flea market a few years back for $12 or $14 or something like that, and it pretty much came straight home and onto the "broken" pile. the seller had said that all that was wrong was that the power switch had been bypassed (why someone would do that i have no clue), and i didnt feel like messing with it at the time so on the pile it went.

i finally decided that i have way too much crap laying around, and that coupled with the fact that i need to trade in some gear to pay off a sweet hiwatt dr504 finally motivated me to stop being lazy and go through the pile and fix up some of the "junk" (and on top of that, any little bit of repair knowledge i can teach myself tends to prove invaluable in my job as a guitar repair tech in a music store). im not exactly a stranger to the inside of an amp, ive done basic repairs on several of my tube amps, but im not all that familliar with solid state.

well, first things first, i wired in a new power switch and plugged it in(with the test lamp in series). flipped the switch and......no power at all. checked the fuse.....blown. replaced the fuse, flipped the switch and....on goes the test lamp. from prior experience with tube amps, first thing i checked was the power transformer (good) and the rectifier diodes (good). at that point i was a bit stumped, not knowing what else to do, so i did some research and came across this site and read that blown fuses in ss amps are usually a result of bad output transistors. so i pulled them out and sure enough, they were both shorted out. the only markings on them were "p 4091", which after a few hours of searching led me to pretty much nothing, and being as this is a pretty old ss amp (1966 or so), i wasnt exactly optimistic about finding replacements, and i couldnt find a schematic anywhere. i finally tracked one down by downloading the gibson master manual, and looking at the parts list it listed the output transistors as 2n3055, and upon searching that i was shocked to find out that they actually carry them at radio shack (something that quite possibly has never happened to me before-radio shack actually having what i needed.......). so i went in and picked up two of them and installed them. i held my breath, flipped the switch and.....on goes the amp. victory! or so i thought.......which finally brings
me to my problem.

i hooked it up to a cab, and plugged in a guitar. first the bass inputs. i got sound, but extremely low output, and a bit of a hum. then came the guitar inputs. super low output again, and on top of that an oscillation which seem to be activated by the treble knob, but changes pitch when any knob in the guitar preamp or the effects section is turned (actually sounds really cool, but.........). could bad electrolytic capacitors be the cause of both the low output and the oscillation? im also guessing i probably need to bias? any other suggestions?