Conflicting Original plexi schematics. Need origianl schems

[Guest]

I've been searching the net, but can't find schematics for converting my 76 to original plexi specs. Can someone point me in the right direction?

[Billy Batz]

Your 76 probably is no different then many amps from the plexi era other then spec wise. But circuit and value wise its probably the same. Its not a MV is it?

If your referring to the JTM era Plexis then theres a few big differences and two of them are Transformers and filtering. I prefer JTM100s myself. If You want I can send you a bunch of schems.

[Guest]

So without replacing th trannies, what is th most desireable circuit?

[Billy Batz]

There is no one desireable circuit. Some people prefer the older JTM 'shared' circuit and some prefer the later 1959 'split' circuit and some people prefer the later Super Bass circuit which is almost exactly like the JTM circuit accept for filtering and trannys.

While I am biased Ill try and give some pros and cons for each circuit. The early amps are much fatter, warmer, rounder, smoother and larger sounding and sing but they can be bassy, boomy, flabby and tubby and with stock filtering from the time can ghost a lot. They hav more chime and less gain. More ring and less compression. The later split cathode amps like 1959s are brighter, tighter, higher gain, more saturated, more compressed but they can be a bit thin and trebly, some would say harsh, and lack the big sound of the early amps. Some people consider the more compressed sound good. Others wouldnt. One thing is certain. Many amps on classic songs people always thought were Plexis were really metal panels. What sound are you going for?

Its my understanding the main difference in a 76 and 68 era split cathode amp with the Power Tranny is the voltage is much lower which would make the gain a bit more saturated and squishy. More EVH or 70s rock. Mostly what your looking at is replacing components with better quality components. If you read some other threads theres been a lot of mention of that today. Late 70s amps that come alive with a new board and in some cases a new OT. Replacing filter caps may be a great first step. Tubes a second. Then if you feel you want to go with it replacing the signal caps on board with Sozos is another step. Or you could replace the whole board as many have done to make changing components and tweaking much easier. I cant speak for everyone but for myself and most people here changin out parts is a pretty common thing and its not easy at all with a PC board.

[Guest]

There is no one desireable circuit. Some people prefer the older JTM 'shared' circuit and some prefer the later 1959 'split' circuit and some people prefer the later Super Bass circuit which is almost exactly like the JTM circuit accept for filtering and trannys.

While I am biased Ill try and give some pros and cons for each circuit. The early amps are much fatter, warmer, rounder, smoother and larger sounding and sing but they can be bassy, boomy, flabby and tubby and with stock filtering from the time can ghost a lot. They hav more chime and less gain. More ring and less compression. The later split cathode amps like 1959s are brighter, tighter, higher gain, more saturated, more compressed but they can be a bit thin and trebly, some would say harsh, and lack the big sound of the early amps. Some people consider the more compressed sound good. Others wouldnt. One thing is certain. Many amps on classic songs people always thought were Plexis were really metal panels. What sound are you going for?

Its my understanding the main difference in a 76 and 68 era split cathode amp with the Power Tranny is the voltage is much lower which would make the gain a bit more saturated and squishy. More EVH or 70s rock. Mostly what your looking at is replacing components with better quality components. If you read some other threads theres been a lot of mention of that today. Late 70s amps that come alive with a new board and in some cases a new OT. Replacing filter caps may be a great first step. Tubes a second. Then if you feel you want to go with it replacing the signal caps on board with Sozos is another step. Or you could replace the whole board as many have done to make changing components and tweaking much easier. I cant speak for everyone but for myself and most people here changin out parts is a pretty common thing and its not easy at all with a PC board.

Thanks for the input. I used to have a 74 bass jmp that I though sounded better to my ears than the 76 lead. I was told at 1 point that the circuit in the 74 bass was closer to the "plexi" specs than the leads of the same era?

I did this clip with my old 74 bass JMP and a pedal in front of it

http://home.comcast.net/~scottosan2004/GNR.mp3

I don't know if its fair to compare, but I think the bass jmp like the pedals better.

[Billy Batz]

Its true. I dont have an exact figure but Ill bet something like 90-95% of the amps that actually got a plexi panel were shared cathode JTM amps which Basses are very similar to accept for a few things.