ORIGINAL MESSAGE:
On Mon, 26 Nov 2012 19:36:21 -0500, Steve wrote:
>Want to re-do the input matching of an old HB 8877 amp. What should I use for
>the cathode impedance when calculating my pi network? I recall it was
>something like 50-60 ohms.
REPLY:
The cathode impedance is close enough you don't need any impedance matching. I
built my homebrew 8877 amp with only a simple parallel resonant circuit in the
cathode circuit to provide the 'flywheel' effect needed for good IMD. I used a Q
of five on all bands. Each band has it's own small toroid coil and a mica
compression trimmer for tweaking.
Works great on all bands except 160 and 80 meters where I have to turn on the
tuner in the transceiver at the high end of the band. The other bands are flat
enough across the whole band.
If I were doing it over I would also install a trimmer capacitor adjustable from
the front panel for fine tweaking.
73, Bill W6WRT
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