[HBR] Octals and such

[Ian Wilson]

Interesting. Thought I had read all the useful projects in the 15th
Edition but had never looked this one. I wonder why he used a
6BK7A in cascode mode rather than a small pentode?

I have pondered making (a) receiver and/or transmitter using
only 6AC7's. For some reason I have lots of these, most seemingly
NOS. As a late era octal I would guess it would have pretty good
stability; the gm is much higher than the classic tubes used in octal
receiver IF stages; and you can bias it into a remote cutoff mode
of operation. The real estate for doing an HBR-type receiver would
be pretty large, though (and buying a fixer-upper HRO is probably
a better idea anyway).

Yep - that list of interesting things to do never gets any shorter!

73, ian K3IMW


On Sat, Nov 22, 2014 at 8:10 PM, Walt Hutchens <waltah at earthlink.net> wrote:

> 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
>
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