> (1) A rather unusual "manual" soft-start circuit
This is a Henry Trademark; used on many of their models. You just have to
remember not to pause as you turn the switch from or to the "off" position.
>
> (2) The grid metering is done directly, for some reason...?
This is another Henry SOP. I like it because you can calibrate the grid
current meter with the pot. In the grid circuit.
>
> (3) Operating bias looks to be established with a zener, but I really
> don't understand the combination of RF choke and feedthrough cap that
> appears to short the filament transformer center tap to one side of the
> filaments... I must be looking at that one wrong!?
The filaments are hooked in series. (Typical Henry again.) Each side of the
filament transformer goes to one of the filament pins on the two tube
sockets. The other two filament pins are hooked together, and go to the
center-tap on the filament transformer. This gives you 10 volts total; 5
volts per tube in series. The RF choke in the center-tap line keeps RF out
of the filament transformer. The capacitor next to the RF Choke is a
feed-through cap through the chassis wall. The large filament choke keeps
the RF out of the filament transformer also. When you key the amp, a relay
shorts out a resistor in series with the zener and changes the state of the
tubes from cut-off bias to operating bias, which is established by the
zener.
I did not mean to write an epistle here, but you sounded truly interested in
how things work.
(((73)))
Phil, K5PC
>
> Any comments, stories etc?
>
> Thanks,
> Jim, N7CXI
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