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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