Marshall EL34 100/100 Poweramp schematic

[RomanMtz]

Hello!

I was wondering if anyone knew where I could find a schematic for a Marshall EL34 100/100 Poweramp. I'm trying to troubleshoot one for a friend. It has damaged on a flight and one of the channels outputs this strange buzzing noise with almost no guitar output. If you raise the volume, you can hear the guitar through the noise but almost as if it had a weird ring mod effect to it.

At first I thought it was the tubes being that I received the amp with the phase inverter tube knocked out... but I tried the tubes of the working channel in the non-working one and it was no go...

I'm thinking it could either be a blown transformer, power supply component (cap) or a loose solder joint somewhere.

I haven't gone through the hassle of disassembling the whole amp yet. Any insight that might point me to the right direction?

Thanks in advance!

[bluesfreak]

Are you referring to the 9200 2x100W 19" Poweramp?
You can find the schematic here: Marshall Amps Info & Schematics

[RomanMtz]

I don't know if that would be the same as this:

Buy Marshall EL34 100/100 Dual Monobloc Amp | Power Amps | Musician's Friend

From the manual it seems like it is... I'll dive into the schems a little more...

Any insight on my problem

[RomanMtz]

Seems that the 9200 was a predecesor to the EL34 100/100... don't really know if there were any major changes to the circuit though...

[Enzo]

Check the DC voltages on all the tube pins. Got screens on ALL the power tubes? Got reasonable bias levels? And the small tubes, is there plate voltages on 1 and 6 that make sense? Are the cathodes looking alive? Either a volt or two for gain stages or higher voltage for any cathode follower.

If that is OKO, put the same signal into both channels and look at the signal pins with a scope and compare the working channel to the bad.

[Enzo]

Here is the schematic set.

[RomanMtz]

Enzo... much much appreciated.

Will look into the voltages this weekend and report back. Thanks!

[Lee_ranaldo]

that amp has 1 transistor connected to cathode (it's an MPSA45 if my memory is not cheating on me)

that one just connects the triode cathode to ground . I've seen those totally blown up in those amps

also they use 1/4W resistors , check screen grid resistors (usually soldered into power tube sockets , must be 5,6K )