> Very simple circuit.
> One resistor for cathode bias.
> Bypass cap for cathode (audio freq, 10mfd or so)
> Output transformer.
>
> Is the same circuit good for a broad band RF amp?
No, for multiple reasons. The list would be a long one.
> Transmission line tranny for output. Perhaps an extra
> winding for degenerative feedback.
Not a chance of that working, unless you run a tube that has a
darned low operating impedance and yet has insignificant output
capacitance.
> I'm thinking bargain basement amp here. 813 tube
> microwave oven transformer, transmission line wound
> on surplus toroids.
Microwave transformers have poor ESR, it is intentional in the
design, so they make crummy power supplies for load-varying
capacitor input systems.
Transmission line transformers are tough enough to make at low
load impedances, and almost impossible with loads over several
hundred ohms. They are worse yet when high transformation ratios
are required.
You'd be better off using a low-Q network, one for each band or part
of the band.
73, Tom W8JI
w8ji@contesting.com
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