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#1 2013-02-18 17:58:16

simondolanbass
Member
From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
Website

V4 power tubes, bias and Hum

Hi,

I read that V4 are prone to humming. The hum in mine is unaffected by preamp tubes.

I read too that mismatched power tubes can cause hum. Are matched tubes will have the same bias current? Mine have two tubes at 46 mA and two at about 32 mA. Can we say that this reading is causing the hum?
Not sure about spending 100$ bucks on power tubes and not improving the hum issue...

The filter caps are spragues and ac ripple is low (except on the middle tap on the OT it's 7.5 VAC)...

Thanks

Simon

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#2 2013-02-18 18:44:46

hangman
Banned
From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: V4 power tubes, bias and Hum

Have you checked the hum balance pot?  It that is defective you will get a hum also.
Power tubes are likely not the culprit.   And 7.5 VAC on the OT is normal at idle
I have always found my vt22s to be rather quiet.   Very little hum.

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#3 2013-02-19 10:25:54

simondolanbass
Member
From: Montréal, Québec, Canada
Registered: 2011-11-28
Posts: 14
Website

Re: V4 power tubes, bias and Hum

Hi,
The hum balance pot does change something but not in the 60hz range. It change something higher . I measured the hum and it's 60 hz.

There is a 3 prong ac plug but the green wire is not connected to chassis. Can it help to rewire it properly for the humming? What do I need to do with the polarity switch and hum balance pot connection?

Simon

Last edited by simondolanbass (2013-02-19 12:51:08)

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#4 2013-02-19 10:32:09

hangman
Banned
From: Seattle Washington
Registered: 2006-09-03
Posts: 1848

Re: V4 power tubes, bias and Hum

The green wire is there, but not connected?   That is strange.   I would connect it to the chassis,  that is what it is for.

That might help with the hum

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