[Amps] Alpha PA77 vs 77Dx plate choke?

[Rob Atkinson]

What's the total value of the bypass caps in the 77Dx?

tnx

rob
K5UJ

On Mon, Jun 18, 2012 at 1:01 AM, Jim Barber <audioguy at q.com> wrote:
> 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.