On Fri, 12 Feb 1999 18:09:12 Scott Townley <email@example.com> writes:
>I've followed the thread on cathode-driven input networks using
>and the general advise that coax between the "tank" and tube filaments
>Although I have not seen a great many amps in my day, the few I have
>"pigtail" the coax runs...no connectorization inside the amp at all.
>would seem to me (and I've measured it as well) that the shield
>is poison to achieving good input matches at 21 MHz and above.
>the introduced inductance would be that much worse at 3rd and 5th
I wonder if the harmonic content has any measurable effect.
A modern xcvr has >40 dB harmonic attenuation. A good LP filter has 70+
dB attenuation at the 3rd harmonic. So to paraphrase " Where's the beef?
I dont know about others but I run a good LP filter between the rig and
the amp as well as one at the amp output. I have had no problem with
efficiency on 10M or any other band with an LK-500, LK-780, PT-2500A or
any other amp with long RG-58 runs to the tube.
Might the problem in certain amps be unbalanced currents on the outside
of the coax shield? Perhaps a ferrite sleeve balun might offer an
Are there specific amp models that are more prone than others?
73 Carl KM1H
>My question: is it really the coax itself that causes such pain in
>input, or is it the lack of proper coax termination? Would using
>bulkhead/panel fittings allow for remoting the input network the
>traditional 6-12" from the tube filaments?
> Stoddard Aircraft EMI/RFI receivers and accessories
> Big Parts for that Big Linear Amp
> 70's era RF test equipment HP/GR/Tek
> Radio-related technical reference material 1940+
> http://www.primenet.com/~nx7u (someday might have useful
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