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Help! My JCM 800 is acting strange!

Azaril000

Member
Messages
82
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.
 

yabasta

Member
Messages
250
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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