If your theory is correct concerning tube gain (Mu) how do you explain this:
A gs-35b requires around 40 volts bias for zsac of 150ma with 4kv Ep...A
8877 at the same Ep requires much less for similar zsac. The gs-35b is a
lower gain tube than the 8877...Did you mean: It takes more negative bias to
reduce anode current as the mu is DE-creased? The inquiring minds want to
know..73, Jim..
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "k7rdx" <k7rdx@charter.net>; "Amps" <amps@contesting.com>
Sent: Tuesday, July 18, 2006 9:28 AM
Subject: Re: Life and gain of 3-500Z
> > The tubes (3-500z`s) were from RF Parts. I replaced (Henry
> > 3K repair
> > job)some low hr Eimacs that one had developed a grid to
> > filament short. Gain
> > was compared to a nos pair of Eimac`s.Higher zsac for a
> > given Ep and close
> > to 10% more output for a given value of drive.Jim..
>
> The trend is generally this:
>
> Higher quiescent current for fixed bias and HV generally
> indicates lower mu, not higher. It takes more negative bias
> to reduce anode current as mu is increased.
>
> Lower mu generally indicates higher input impedance, more
> negative feedback, and less gain in a g-g amplifier. In a
> g-g amp gain is mostly determine by the ratio of load
> impedance to driving impedance, and higher mu tubes
> generally have a lower cathode drive impedance.
>
> It would be interesting to see what the Chinese are doing
> differently when they make the tubes. Maybe the tubes are
> lower mu and lower driving impedance?
>
> 73 Tom
>
>
>
>
>
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