[Amps] Life and gain of 3-500Z

[Tom W8JI]

> 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