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Do tubes buzz just before they die?

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Do tubes buzz just before they die?

Postby ManFromGlass » Fri May 29, 2020 12:29 pm

I turned on my 20 year old ART Tube Pac pre yesterday. The unit is now making a quiet hum/buzz but the audio seems unaffected. I’ll do a bit more testing.
My first thought was the tube is on it’s way out. Do tubes make noise before they die?
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Re: Do tubes buzz just before they die?

Postby Hugh Robjohns » Fri May 29, 2020 12:37 pm

Sounds like an acoustic transformer rattle to me. it might go away once the unit has warmed up...
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Re: Do tubes buzz just before they die?

Postby ManFromGlass » Fri May 29, 2020 12:49 pm

Searching the internet has found a few similar problems. One fix involved resoldering some wires near the PCB socket but I’ll try letting the unit warm up for awhile before trying surgery.
As long as the hum isn’t in the audio signal I’m happy as the unit really brings a cheap bass I have alive and in a pinch is fine for mics too.

I asked about tubes as a guitar player friend made the suggestion and aside from the ART unit I have little experience with tube gear.

cheers!
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Re: Do tubes buzz just before they die?

Postby James Perrett » Fri May 29, 2020 2:40 pm

Acoustic hum is likely to be the mains transformer and, in my personal experience, American made gear is very prone to buzzing transformers - possibly because they don't make sufficient allowance for the different mains frequency in Europe which requires a larger transformer. If this noise is new then it is probably caused by loose windings or possibly by something drawing more current than it should. I'd check to see whether the case near the transformer feels hot after a while.

If it is electrical noise on the output then I'd check all the ground connections and check for bulging capacitors.
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