The 77's were shipped with a B&W 800 choke and 160 wasnt considered
important before the US was authorized 1500W. The next step was the 801
which was better on 160 but fried on 12M when we got the WARC's. Next came
the 802 which solved the WARC's but was light on 160.
OTOH, having a part of the plate choke become an active part of the 160M
tank is rather common in several ham amps. How well it works depends upon
the designers and many opt for the Ameritron choke where it fits.
Palstar (no longer in production but some stock is available last I heard)
and QRO chokes fit the 77.
The 802 is still available at an outlandish price.
Carl
KM1H
----- Original Message -----
From: "Jim Barber" <audioguy@q.com>
To: <Amps@contesting.com>
Sent: Monday, June 18, 2012 2:01 AM
Subject: [Amps] Alpha PA77 vs 77Dx plate choke?
> I'm getting around to servicing the blower (again) in my very last
> complete Alpha PA77, and decided that since I'll have the side off I
> might as well add the toroid and caps to put it on 160m. Note it's been
> 20 years or so since I've done this, so memories are a bit foggy... :-)
>
> Many things confuse me, but what's relevant to this discussion is that
> the plate chokes for *both* the PA77 (10-80m) and the 77Dx (10-160m)
> appear to be 90uh on a ceramic form plus a 15uH molded choke in series.
> The 77Dx also has a smattering of additional bypass caps, (that part
> makes sense) but isn't a total of 115uH a bit light for 160m? There's
> room to put in something like an RFC-3, but I'm wondering what the
> original strategy was, assuming anyone remembers.
>
> I also notice the the 77Dx has no tuned input in the 160m position. I
> can probably ring out the approximate cathode impedance "offline" by
> putting 50 ohms (or so?) between the cathode and ground, pulling in the
> input relay then putting the VNA on the input connector. What I find
> puzzling is why there would be no tuned input for 160m on the 77Dx,
> since it was shipped as being capable on 160m.
>
> Any remembrances?
>
> Thanks,
> Jim N7CXI
>
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