[Amps] Grid resonance

[Steve Thompson]

Steve Thompson wrote:

Sorry, should have said this was on a 8877.

> A had a few minutes before leaving the office yesterday, so I fired
> up the network analyser. I made some rough, not precision,
> measurements and, as these were done on a cold tube lying on the
> bench I'm uncertain as to how useful they are.
> 
> I measured the impedance between the grid ring and one cathode pin.
> At low frequencies it's capacitive. As the frequency increases the
> inbuilt inductance comes into play and series resonance occurs at
> around 250-270MHz. The impedance then goes inductive until parallel
> resonance at about 1.7GHz. 
> 
> I also looked at feedthrough, feeding into the cathode from a 50 ohm
> source and measuring into a 50 ohm load at the anode. From 1-2000MHz
> the feedthrough
> is around -60dB except for around 250MHz and 1.7GHz where it comes up
> to around -45dB.
> 
> Steve
> 
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