[HBR] Plug in coils revisited

[Walt Hutchens]

A couple-three weeks ago there was a brief discussion here of how one
might do plug in coils for an HBR in a manner similar to the HRO, that
is, with a single assembly holding all the coils to facilitate
changing. (And perhaps keep the high voltage hidden?) Browsing old
Radio Amateurs Handbooks the other night I saw another idea. Those
with a 1958 copy of the Handbook can turn to p. 463, "A Mobile
Converter for 3.5 through 28 Mc."

This builder used the common 4" x 2" x 2" aluminum boxes for the coil
sets. He used the part with three 4" x 2" sides in a 4" long 'U' for
the coil set chassis, putting 4-pin plugs in the center section,
mounting slug tuned coils screw end up directly on the plugs, and
drilling matching holes in the cover section. This is a bandpass
converter so no variable capacitors were used, but it would be
possible to add them on the top side of the coil chassis; in fact I
think all but the largest value APC-size caps would fit. It would
doubtless be necessary to add a shield between the antenna and mixer
coils for a tunable front end.

Heck, on most bands you'd be able to use hand-wound coils on PVC
forms, if you wanted. Toroids would be necessary to get the best
performance on the lower bands, though.

This would be expen$ive with all-new parts (so what all-band design
isn't?) and you'd still need to use fairly small coils and caps but
there's enough space to make it work, which the command set coils
DON'T have. I think this is a practical approach to a home-brewable
HRO-style HBR receiver.

It would be a natural with the use of the 6-9.1 Mcs command receiver
tuning cap. Sub-mount the coil sockets so the coil assembly goes in
through a 4-1/4" x 2-1/4" hole in the panel, allow access from the
bottom to adjust the caps, plenty of ventilation around the oscillator
end of the coil set ...

One might even liberate the necessary plugs and sockets from junked
command sets.  Coil changes using 4-pin tube-base type plugs could be
quite a challenge and that's AFTER you find all the 4-pin plugs you'll
need.

A tempting idea ... maybe someday.

Walt
KJ4KV