[Amps] 8877 cathode impedance

[Bill Turner]

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