Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 961le on August 27, 2011, 02:21:24 pm

Title: jcm 900 slx 50w issues
Post by: 961le on August 27, 2011, 02:21:24 pm
just recently after playing my amp for a while, the volume will fade away with a fuzz sound and will then come back to normal volume, this occurs every few minutes. a little background... the amp is a 93 model and i need to replace the caps asap. my question is: will the old caps cause this situation? or, are there more issues under the surface? when its at volume it sounds quite lovely :)
Title: Re: jcm 900 slx 50w issues
Post by: eleventeen on August 27, 2011, 02:29:59 pm
First suspect, with no other information: Yes, the electrolytic caps in the power supply are getting senile in their old age.
Title: Re: jcm 900 slx 50w issues
Post by: Ritchie200 on August 28, 2011, 01:54:24 am
Give your effects loop jack a workout with a plug and some cleaner, maybe re-tension the contact shunt leg if it looks loose.  Try the easy stuff first!

Are you sure the caps are bad?

Good luck!
Jim
Title: Re: jcm 900 slx 50w issues
Post by: 961le on August 28, 2011, 03:52:41 pm
richie, in the past i have had issues with the effects loop. only after i had tampered with it. after a few jabs all was well. the bassy notes usually taper off with a little fuzz in the background. im about to order some f&t's and see what happens. this little sucker gets a lot of bad wrap, but when dialed in its very nice:) ill report back.
Title: Re: jcm 900 slx 50w issues
Post by: 961le on August 30, 2011, 08:43:05 pm
well the answer is yes, bad caps will cause my problems. after i had them removed i checked their capacitance and both were within spec.  at that point i was wishing i had left it alone but i proceded anyway. after the swap the change was very noticable. it sounds wonderful, nice and tight. now after looking at the board mounted caps i was wondering if i should tackle those next? where do you source pcb components? thanks for the replys guys.