Thanks to Dave K6XYZ, Steve AB5MM and Phil K5PC for the very helpful
responses.
Phil, you're right. I am truly interested in how it works, but I'll also
admit an ulterior motive as I'm working on buying one. Not having any
experience with this or other Henry amps, I thought I'd better find out
if there were any major 'gotchas' to the design; especially because of
the age and considering Henry is largely out of that particular business.
So far no 4-alarm fires reported, which was what I was hoping for.
Assuming I end up with it, my wife will be somewhat amused that it will
dwarf my Alpha 77's, which she doesn't consider dainty. Or quiet. Or
necessary, for that matter... ;-)
73,
--jim
Jim Barber, N7CXI
Phil Clements wrote:
>
>
>> (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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