> find a reference that the input impedance of a cathode-fed 811A / 812A
> is approx. 300 ohms.
812's have higher driving impedances than 811's, and less gain in
GG. They also take high bias voltage.
> Has anybody ever tried using a broadband matching transformer, the
> kind used in solid-state amps?
A matching system in a GG class B or AB amplifier serves three
important functions:
1.) It matches impedances
2.) It provides a low impedance path to the chassis for tube
cathode harmonics
3.) It prevents cathode harmonics from reaching the exciter and
causing problems
You can't do that with a broadband transformer. It requires a low
pass network with a low-reactance capacitor (compared to the
tube's driving impedance) shunting the tube cathode to ground.
73, Tom W8JI
W8JI@contesting.com
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