[R-390] 60 Hz HUM Why AC filiments?

[Jim M.]

Personally I have never experienced a high hum level from a tube radio
unless a connector or ground was amiss, a power supply was poorly filtered,
or a tube was bad or going bad such that there was leakage from filament to
cathode.  Normally whatever hum is induced by a normally operating circuit
is way below the signal level as to not be obtrusive,  A filament to cathode
short can induce hum.  Start trying replacement tubes in all stages, if
replacing one causes the hum to diminish, then you have a bad tube.

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Rasputin Novgorod
Sent: Monday, June 08, 2009 2:27 PM
To: r-390 at mailman.qth.net
Subject: [R-390] 60 Hz HUM Why AC filiments?


> Hum seems to be strongly related to
> using AC filament power as opposed to DC.

I must confess that I don't have a lot of experience
with tubes; But pumping AC into a tube seems to me
to be a great way to inject hum. Why did they do it?

Given how cheap and easy diode rectifiers and regulators
are today, should we convert AC filaments to DC?

Sincerely
/b




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