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Help! Fender bassman 500 losing volume

angelopbass

angelopbass

May 18, 2011
279
98
struthers, ohio
#1
So I've had my fender bassman 500 head for about 6 months now. (Purchased new) I was practicing with my band last night and suddenly about 45 minutes or so in to playing, my volume cut in about half! Never had any issues like this before. I turned the amp off for a minute and then fired it back up and all was fine for the next 20 minutes or so of practice. Could this be a tube issue? I know it's under warranty but I don't know any local places that I can't take it to get serviced. And I'm fine with replacing tubes if need be. Any educated opinions? I haven't really heard of anyone having issues with these amps so I'm curious what I can find out from my fellow tb'ers.
 
#2
Is this what happened?

500 Manual.jpg
 
#3
2cooltoolz said:
Is this what happened?

View attachment 954879
Click to expand...
If you open it up and try to fix it yourself, will that void the warrantee?
It's highly unlikely that anyone here can really offer a definitive solution without guessing.
I recommend you call Fender and arrange to get it fixed.
One, non-invasive thing you can do first is check what the manual says about air flow around the unit and be sure you are following their advice. It sounds thermal, that's my guess.
 
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#5
Thanks guys. Talked to the guys at the music shop that it was purchased and they said that they can ship it out. Guess we shall see. I'm running it through a fender rumble 410, with the peak light barely lighting up. (Fender p bass with Duncan qp's) We are a 3 piece with a pretty controlled drummer. No one is insanely loud at practice ever. Hope this can be resolved. But I've never heard of any issues with this amp like this.
 
#6
I had a problem with my SB300 where it would occasionally lose volume after twenty minutes or so, once it was warmed up. I'd turn it off and it would come back to life and mostly run fine, sometimes not - a real pain. Sounds similar to what you described.

I was sure it was tube related or the auto bias but it turned out to be a really simple fault - The preamp out or power amp in contacts needed cleaning ( or replacing. Can't quite recall ). But a really simple thing and a quick fix. My amp has run faultlessly since.

If you can get it to fault again try putting a jumper cable from preamp out to poweramp in.
 
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#8
angelopbass said:
Crap. Wish I would've seen this. Sent it back to the factory for warrantee. I have a feeling this isn't going to be resolved, as it only happened once.
Click to expand...
Please post a follow up when it comes back. I have the SB300. It was doing this. I narrowed it down to the preamp. I swapped the tubes. Still doing it. I decided to clean the send return connects. Problem solved. I think.
 
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#11
So thanks for the replies guys. Update: today I practiced using my backup guitar/bass amp. My fender champ x2 through my rumble 410 (don't knock it til ya tried it. It goes in our merch bin to all shows as a backup amp for guitar and bass) About an hour in to practice, guess what?! Loss in volume again!! I immediately say oh my! It's the cabinet! So I go to unplug the bass, and hear some funky cutting in and out. Ummm. Ya. I can officially classify myself a class A moron. I'm pretty sure my input jack on my bass was cutting the volume. IDIOT!!! Oh well. Hope fender gives me my amp back soon.
 

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