Anyone else have a jcm800 that is suddenly lacking punch?

  • Thread starter Thread starter Kapo_Polenton
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Kapo_Polenton

Kapo_Polenton

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Returned to stock amp (only had a few diff values in preamp to up the gain), new power tubes and filter caps I changed 3 years ago. Was A/B ing this 82' JCM800 with my other one and it lacks balls and cut in comparison. I noticed this after a jam the other night. I felt my tone was bass heavy and these amps generally cut way more. So I was playing with it today and diming controls and I notice the bass POT kicks in very quickly and the treble has less effect. This amp used to cut, I'm wondering what could have happened along the way. I have to dial back the bass pot to 2. Treble doesn't seem to kick in drastically either. I guess amps really can be "good" ones vs. average to poor ones. Anyone experience this? 5 years ago I remember thinking the amp didn't have enough gain but never noticed it lacked cut. Everything is working fine.. maybe my other one is just "a good one" ? Transformer issue maybe? original trannies still in there. Might be time to sell this bad boy otherwise cause I always play the one that sounds better. I just liked this one for a gig worthy amp.
 
Probably already did this but maybe put the same tubes in the 'bad' one and check bias? I know the first time I used Winged Cs they totally changed the character and balls of the Marshall I had at the time. Or maybe filter can caps...people say they really make a difference when they're changed out if its needed..
 
Have you tried changing pre amp tubes? I have experienced inconsistencies when I used to run multiple 2203's and 04's and balancing volume levels. Some just stand out more than others of the same model #, year and tubes.

Perhaps it was the cap job? I have one old 2203 in desperate need of a cap job as it is unusable currently and way too much treble, ice picky, weak and thin.
 
Caps on the board or large 50/50 filer caps? I replaced 50/50 a few years ago with FnT's and the amp has not seen that much use so I wouldn't think that was he issue. Also rolled preamp tubes and no real difference. I spent some time on google and have seen other posts where people complained of the same thing and had to keep their bass low and treble higher. Might just be the sum of all parts and the caps on the board over time I suppose. Other than that, the amp is in perfect working condition and isn't noisy. Just feels a little shy on cut and the gain does seem to be there. Anything past 7 on the preamp and the bottom end suffers.
 
Maybe one, or more than one of the pots is drifting in value or going bad? You could probably google their values and read them with a VOM. You would need to disconnect the leads to them first, to read them properly.
 
Actually, as of yesterday, I think I have a more serious problem which is likely contributing to the lack of life in this amp. Turning up the MV to 5 on these amps should shake the walls. I had it going through a 4 x 12 and I was able to get it up half way without shaking walls. Compare my other two amps at 2 and they louder than my 82 on 5. I have experienced loss of volume and raspiness/fizziness before and I changed the ouput transformer so I am wondering if this the same thing all over again. Maybe after 30+ years of being rocked this thing has met the end?
 
I think I may have found the culprit over on one of the power tubes. Is that me or does that resistor look toasted?
 

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Yes..
Yes it does..
Should be able to check it with a VOM to verify ;)
Check it against the others and see what you get
 
I had a the treble pot go bad on my handwired plexi. Once I swapped it out, all of the volume and punch was back.
 
yngwiestrat":35ype2ii said:
I had a the treble pot go bad on my handwired plexi. Once I swapped it out, all of the volume and punch was back.
Click to expand...

Same thing happened with my Metro. It would cut out on me but no fuses were blowing. Tech found a bad treble pot.
 
Yep that resistor definitely looks burnt out. Replace it and test the amp again.
 
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