[HBR] Octals and such

[Walt Hutchens]

Bill said:

> I thought about building some of the projects, including HBR with
> subminiature tubes. We get an even greater space saving and a
> considerable saving in power consumption and heat, too.

First, I don't want to discourage anyone from striking out. The HBRs
are basic designs, not terribly critical, and if you are ready to do
the stage-by-stage (mostly) minor redesign you can get a
well-performing receiver from octals, miniatures or subminiatures.

I wouldn't recommend doing it for a first full function receiver
construction project though: There's stuff to figure out just because
it is your first. Get one working, THEN do something different!

As to subminiature tubes, I've looked at that and decided against it
for most kinds of projects. It is true that in military sets with 15
tubes and up you can get a considerable space saving but when you look
closely at these sets ALL the parts are subminiature, right down
to the IF cans. The PRC-6 handy-talky of Korea and the next decade or
so puts the entire transceiver in a package that's (ballpark) the size
of a square 6 volt lantern battery: The rest of the case is the
battery, switches, mic and earphone/speaker, and so on.

Also subminiaturized is the wiring. The tubes are socketed and the
wiring is conventional point-to-point, but it is TINY. You're not
going to do much experimenting when wiring at that scale!

In a design with fewer tubes, tiny tubes don't give the payoff you'd
expect and it shrinks even more when you realize that the only
mult-section tubes you get in subminiature sizes are dual triodes. The
triode-pentodes that are so handy in later HBR designs are ONLY found
as miniatures -- not subminiatures. So as with octals you need two
sockets to do the job of one 9-pin miniature. Meaning twice the
filament wiring, etc.

And I was not willing to tackle finding or making the necessary
subminiature other parts. 1/2" IF cans are out there for 455kcs and
262kcs (I think) but 85 or 100kcs, I doubt it. Tuning cap -- small
enough ones are not hard to find but the dial's a problem. And so on.

By adapting the design a bit -- half lattice crystal filter instead of
the double conversion of the the 'real' HBR you could eliminate the
low frequency IFs. Then there's the question of plug in coils. And
when you get done will the thing sit still on your desk when you try
to tune it?

The one ham subminiature design I think might be interesting would be
a variation on the 20M SSB transmitter featured in 15th edition of the
Bill Orr Radio Handbooks in the early 60's. 6" x 9" x 5" and 40W PEP
output. THAT could be tweaked a bit -- most people would want to
simplify the metalwork dramatically and eliminate the unique power
transformer -- and turned into a buildable project. It's crystal
controlled so no dial. A receiver, though, I think you'd want to do
from scratch.

I would, however, start by looking at using 9 pin miniatures in place
of pairs of subminiatures. That handbook is dated 1962 so the best of
the high performance dual section 9-pin tubes were not available when
it was put together. There are also some three-tube SSB transmitters
that might still be usable if you can tame various spurious emissions
-- there's one in the 1962 ARRL SSB for the Radio Amateur handbooks.

Lots of reasons to want to live forever!

Walt
KJ4KV