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Old 6th February 2003, 06:59 PM   #1
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Default Humm

My vintage tube amp has a 500K pot to adjust the volume. It hums when I turn volume past 10'oclock. Any ideas what the problem maybe. It does not hum at all when volume control is at 9'oclock or less.
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Old 6th February 2003, 07:10 PM   #2
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Default HUMMM...

Hi,

Quote:
It hums when I turn volume past 10'oclock.
Most likely it hums all the time,you may just not hear it at lower volume settings.

The taper of the old 500K may well have a different attenution curve compared to what is commonly used nowadays.

The hum may be a ground loop or some injected hum from AC fed heaters.

It is also possible that a filtercap has dried up and lets the ripple through.

Cheers,
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Old 7th February 2003, 02:02 AM   #3
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Ah, thanks for the tips - I will do a check up on those that you've mentioned.
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Old 7th February 2003, 04:03 PM   #4
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Default HF problems?

Just a small warning. I once had a hum develop in my power amp when the volume control went past a point. It turned out to b eHF oscillation - I could see it on the scope. WHile you cannot hear the HF ( RF) its effects filter down ! Check to see if your power transistors are heating up suddenly . The RF is usually of very low amplitude.
Just a word of caution. In your case it might be just a hum loop ----- Hmmmm.
Cheers.
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Old 8th February 2003, 04:24 AM   #5
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Default OK - I will check on that too.

Many thanks.
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