[Amps] FW: FW: plate choke bypass caps

[k7fm]

> I used a vacuum relay (single pole single throw or RJ-1 in a pinch) at the
> center of the two 90uH chokes to connect to a 1000pF cap to ground.  When
> the relay was open you were on 160 meters, when the relay was closed the
> choke connected to the grounded 1000pF capacitor.  Even though the two
> chokes were still in series the first and second chokes by being bypassed
> in
> the center made the plate end choke the active unit.

Alpha uses the same thing in their later amps.  One caution, however, is 
that if the relay is activated while the power is on, then de-activated, the 
capacitor will have a dc charge remaining across it.  Although the bypass 
cap will not hold a substantial charge, it can tickle if you get across it 
when working on the amp.  Alpha has a high value bleeder resistor to prevent 
that from happening.

Colin  K7FM