Fender Bassman 100 making weird noises

[NORCurley]

Hey!

Just bought an old Fender Bassman 100 that is in need of some adjustments. I'm not very experienced with repairing these kinds of amps, but i'm hoping on some help from some of you more experienced guys on here to at least do some diagnostics.

I've added an audio sample of the sound. It is not constant, but seems to only apply to some tones and above a certain volume. At 0:39 you can hear me smack the top side of the amp and then the noise disappears. In addition I can only see a glow in two of the four tubes, perhaps this might be a part of the problem?

Before you ask: Yes, I have changed every other part of my signal chain. Bass, cable and cabinet.

Thanks!

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[RickenBoogie]

Tube amps are not user serviceable. You need an amp tech with all the diagnostic tools and know-how to properly service/repair this amp. There are no shortcuts.

 

[NORCurley]

Tube amps are not user serviceable. You need an amp tech with all the diagnostic tools and know-how to properly service/repair this amp. There are no shortcuts.

Hi RickenBoogie

Maybe I was a little unclear, but if you read my original post a little more carefully I'm mainly asking for help to diagnose the problem, not a guide to repair it.

 

[B-string]

Sounds like a microphonic tube, if you can't see two of the four big tubes glowing that is not a good thing and the amp should NOT be used with two "dead" tubes. Have you checked for the "glow" in the dark? Some makers hide the heaters (the only part that should glow) inside pretty well.

 

[RickenBoogie]

Unless it's as simple as a bad tube, you'd need an oscilloscope to diagnose the issue. My standard operating procedure with ANY used tube amp includes a trip to my amp tech for a complete check up and cleaning. Usually costs no more than $60, and I consider it part of the price. Totally worth doing, if you want the amp in top form.

 

[B-string]

Unless it's as simple as a bad tube, you'd need an oscilloscope to diagnose the issue. My standard operating procedure with ANY used tube amp includes a trip to my amp tech for a complete check up and cleaning. Usually costs no more than $60, and I consider it part of the price. Totally worth doing, if you want the amp in top form.

+1 can also save you from doing additional EXPENSIVE damage from running an amp with say "DEAD" power tubes

 

[megafiddle]

In addition I can only see a glow in two of the four tubes, perhaps this might be a part of the problem?

Are you talking about orange glow (heaters) or blue glow (fluorescence)?

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