JMP 50w Lead 1971

[cbass]

I think alot of folk think old marshalls were 500+ because they tend to eat tubes and arc sockets etc. I think it more the lack of screen grids and the bias voltage being applied after the standby.

Sure i agree..like by the tube manuaul says 700B+ max for a EL-34 off top o my head??

Yup its not the plate voltage its the screen voltage\current

[Reeltarded]

Super Leads here are in the 490 ish range. 50s in the 450 ish range.

71-2 50s are angry little bitches, but smooth.. a little smooth. Mostly angry!

[Big Al]

Billy, nice amp! Very clean.

By any chance, have you ever tried a 500pf disk in place of the stock 5k Lenco? My '74 JMP50's was removed when I got it. I have to reform the caps and go over everything before I fire it up. Planning to temporarily mount a 3-position bright switch to test both values.

[billyz]

Billy, nice amp! Very clean.

By any chance, have you ever tried a 500pf disk in place of the stock 5k Lenco? My '74 JMP50's was removed when I got it. I have to reform the caps and go over everything before I fire it up. Planning to temporarily mount a 3-position bright switch to test both values.

I believe the later models have a ceramic disc treble cap accross the volume pot. Not much difference to my ears. I don't like either and always lift one end. Very popular with the folks I run with. If I was to use a cap there it would be a polystyrene, sweeter, but the ceramics have a certain grit and can add some microphonic mojo, I suppose. Just my 2 pennies.

[billyz]

Billy, nice amp! Very clean.

By any chance, have you ever tried a 500pf disk in place of the stock 5k Lenco? My '74 JMP50's was removed when I got it. I have to reform the caps and go over everything before I fire it up. Planning to temporarily mount a 3-position bright switch to test both values.

I'm pretty sure the 74' had ceramic,if I remember they were a dark green, at least the last one I worked on did. Cuz I lifted one end for the owner. He liked it much better.
By the time you have a .68 cathode, .002 coupling and 470pf mixer bypass, you have plenty of high end.
I think the lemco cap is ceramic on this one, btw.

[Roe]

I think alot of folk think old marshalls were 500+ because they tend to eat tubes and arc sockets etc. I think it more the lack of screen grids and the bias voltage being applied after the standby.

50s had low voltages and zero or 470R screen resistors

100s had high voltages and 1k screen resistors. Both can be hard on tubes