Hi Pete,
Filament current on the 3-500Z is around 15 amps per tube. Fourty millohms (.04
ohms)
of contact resistance, for instance, is enough to drop the filament voltage by
0.6 volts,
or 12% of the nominal filament voltage (Vf nom= 5.0 Volts). I don't know where
the cathode
emission of the 3-500Z really starts to fall off, but one can easily see that
it doesn't take
much extra contact resistance in series with the tube filament to have a
significant effect
on the filament voltage and ultimately the electron emission. Since the
filaments got noticeably
brighter after the contact treatment, I suspect that improved cathode emission
was the
mechanism responsible for the increased output power.
73 de Mike, W4EF.......
---- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <amps@contesting.com>
Sent: Wednesday, October 10, 2001 2:15 PM
Subject: [AMPS] Filament resistance and power output
>
> I resoldered the filament pins on the ailing 3-500Z, and then put it in the
> opposite socket, thinking that the spring tension might be better there. I
> also rebent the spring clips on the original socket and cleaned and treated
> the filament pins with Caig ProGold GxL, which is rated for use up to 400C.
>
> When I fired the amp up, with the originally OK tube in the not-OK socket,
> I was surprised to see that tube's filament was noticeably brighter than
> the other one. So I repeated the ProGold treatment on the other socket,
> and the filament brightness equalized at the higher level. Then I turned
> on the amp, and was startled to see that my output had increased 100 watts,
> with the same drive and other conditions.
>
> I don't quite understand what's going on here. From time to time I've
> heard amazing things about Caig's products, such as Deoxit, but this was a
> new one on me. What's the physical explanation, if any?
>
> 73, Pete N4ZR
>
>
>
>
>
>
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