John Phillips-JCM 800?

[IIIBOOMERIII]

I have an 83 or 84 JCM800 2203. When I turn this amp on, it
will buzz for about 2-4 minutes and then the buzz goes away.
With the exception of the buzz when the amp is first turned on,
it is a very quiet amp, even in melt your eye balls typical
Marshall mode.

This never really bothered me and it has gone on for a few years
now. But, now that I am a little more hands on with my amps, I
would like to track the problem down. Any suggestions as to how
to start the trouble shooting? I am guessing that because of the
age of the amp it could be a filter cap problem, as I have never
had to have the amp serviced. The only thing I have had to do
to this amp is changed tubes.

Now I have changed 2 or 3 resistor values in the pre-amp
section to get a tad bit more distortion. However, I had this
problem with the amp before I did this mod.

Thank you in advance John and anyone else who wishes to chime
in.

Eddie

[John Phillips]

I don't really have a good idea, except that it probably isn't the filter caps. It's more likely to be something like a resistor or joint with a crack in it that warms up and makes contact... or a ground screw connection.

[SatelliteAmps]

Could even be a cold solder joint.

[IIIBOOMERIII]

Thanks John and Satellite.

[donnyjaguar]

This is where cool-it spray comes in handy. You spray components with the cool mist until the fault returns and there's your culprit. This is shoddy troubleshooting in my opinion, but its what the old TV repairman used.

[IIIBOOMERIII]

hahahaha what a great idea!!!! I am going to have to try that. Such a simple solution. Thanks Donny