18Watt.com

dum dum dum!

i have an ol Marshall 9005 50/50 power amp which i hotrodded and i like it a lot. Its a good 10 years old. Ive been noticing lately that when i turn the standby on it sort of crackles and pops and makes strange noises if i keep playing my guitar. it doesnt mute (even after a 5min or so) completely. do i have a capacitor issue on my hands? could anything else cause this?

thanks

danelectro,
I had one of those power amps in for repair with the same problem.
It turned out that the volume pots were bad. By the way, when you say mute I take it to mean that the noise doesn't go away?? You might also clean all your jacks.
hope that helps---Cliff

ok thanks for the tip, ill clean my pots and see if that does anything.

speaking of pots, in your experience did the presence knobs do anything? as far as i can hear mine do nothing..

oh and i meant that when i have it in standby it never goes completely silent no matter how long i wait. i believe it used to go silent within seconds like a standby should

thanks again

Sounds like your Presence pot is shot then. You should get an adjustement of the high-end sparkle in the sound...

yeh thats what it should do in theory. altho ive heard of ppl saying before these amps have about useless presence pots. i was just wondering if hed agree w/ that. maybe its time for some new pots! woot, small project to hold me over until i get my chassis and transformers

attached is the schematic to my power amp.. im unable to read the value on the presence pot.. can any of you make it out or make an educated guess as to what it should be?

again, thanks

looks like it says B4k7. so linear 5k. if your presence pot isnt worn out completely you could measure it.