Help! My JCM 800 is acting strange!


Hi all,

Not to long ago I purchased a JCM 800 (2-3 weeks).

On two occassions, one including tonight my JCM 800 2204 1986 50w has started to make weird sounds after being on for about 1-2 hours. I was jamming out in the bedroom when the amp started making popping/crackle sounds but in a "heartbeat" rhythm, like on of them old cassette players running (this was on the low sensitivity input). On the high one it still makes this sound but has a very loud hiss/hum which is overpowering at volumes like 3-4. I tried a new speaker, no luck, unplugged all my effects no luck. I let it cool down, the heart beat like popping/crackle has stopped, but there still is a loud hum significantly on the high input (low seems relatively ok). It was absolutely fine before. It made a similiar noise a couple days ago i took no notice, but now it continued a while.

I've managed to record the two sounds, one on the low input the heart beat like pop/crackle and the high input hum/fizz:

SoundClick artist: Azaril - page with MP3 music downloads

For both the recordings the volume on the marshall was around 5-6, mic was a cheap pc one. The pop is very irregular to the usual tube amp popping/crackle as it does it in a pulse rhythm.

I've not even had this long, and its giving me troubles.

Please any advice on what could be happening? Really upset regarding this. I thought the Marshalls were built like a ox back in those days.


try switching preamps around, if you have any replace them one by one, maybe you could target that out.

could be anything. maybe a resistor, who knows.

try the cheap thing first, preamps, power tubes etc.

if that dont do it maybe take to a good tech.

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