Marshall 800 losing power

[SEAN RAF]

I have a Marshall 800 series 4104 combo which is losing power. I can use it for around 5 minutes before the volume drops to an almost inaudible level. When I go to turn it off, it has a sudden, millisecond power burst...I've changed the EL34's...anyone have any ideas?

[OnlineStageGear]

It might be a bad solder connection. As soon as it warms up it loses the connection. Very common failure in Amplifiers, especially ones that get moved around a lot.

Matt

[Twisteramps]

Sounds nuts, but if it has an fx loop put a cable in there. sometimes the switch gets dirty and will cause all sorts of problems.

Pete

[dinky kustom]

how old are the pre amp tubes?

[jcm800x]

I had the same problem with my 800 once. An effects loop was added in the 80's and the solder joints were acting up. My tech removed the loop and wired it the way it was supposed be, now it is loud as hell as it should be! Caps go bad and other electronic parts as time rolls on, James Byrd says on his site that he changes the caps and tubes in his Marshalls frequently.Worst case may be the output transformer, a good tech who knows Marshalls should fix it up quick.

[SEAN RAF]

Pre-amp tubes are less than 6 months old.

[dinky kustom]

Pre-amp tubes are less than 6 months old.

ok rules that out mine did a similar thing ,that was the effects jack,i cant remember if it was send or return .

[thebisch]

ok rules that out mine did a similar thing ,that was the effects jack,i cant remember if it was send or return .

That doesn't rule out anything. I recently had a new 12AX7 die on me in a month. I would try swapping in a different PI tube and then go from there.

[Cleveland Metal]

Yeah, tubes can die quickly, had them poof almost immediately, within hours, weeks or months...

[mountain dave]

Another vote on checking your effects loop. I got a steal on an 88 JCM 800 2205 because the volume would fade off to nothing. After cleaning the effects loop's jacks with some fine sandpaper and a few shots of contact cleaner, it worked perfectly and has for the last year.

[SEAN RAF]

There isn't an effects loop on this Marshall, just a direct out.

[thebisch]

Another vote on checking your effects loop. I got a steal on an 88 JCM 800 2205 because the volume would fade off to nothing. After cleaning the effects loop's jacks with some fine sandpaper and a few shots of contact cleaner, it worked perfectly and has for the last year.

You are right, but a 4104 doesn't have a loop.