[HBR] Blog post about HBR receivers

[Peter Bertini]

Walt

The HR-10 half-lattice crystals might make a passable SSB filter, but for CW
I'd prefer having an IF at 85kHz. Notch filters, variable IF BW, more stable
BFO generation, and an effective Q multiplier would be the reasons I'd opt
for dual conversion.

This opens another bucket of worms -- the AM BW will be too restrictive.
I've thought about a separate simple AM IF (single conversion) at 1682 kHz,
and then going double conversion for SSB and CW.  But then my brains starts
to hurt and I have to stop thinking for a while and take my meds.

Pete

Pete

On Tue, Jun 15, 2010 at 7:09 PM, Walt Hutchens <waltah at earthlink.net> wrote:

> Pete said:
>
> > I subscribe to the belief that the HBRs were intended to be a work in
> > progress.
>
> Yep. That's half the fun!
>
> > For my own effort I'll be adding a few sets of the half-lattice
> > xtal filters (1682kHz) recovered from three HR-10 Heathkit donors for a
> > six-pole filter at the first IF.
>
> The reason for the double conversion design was to provide
> selectivity that the hams of the late 50's-early 60's couldn't afford
> to get via a crystal filter.  If you're going put in those filters --
> and the number used in the HR-10 would be ample -- I would do the
> whole IF at that frequency.
>
> Double conversion has its own problems -- another set of images to
> manage, another mixer to give you distortion, another oscillator, an
> extra tube and socket. If you don't need it, then who needs it?
>
> Can you also steal IFTs from the HR-10?
>
> > I'm also considering a 6GM6 RFA, 6ES8 Pullen mixer, and 6EJ7s in the
> > IF stages.
>
> I would use the 6EH7 in the RFA and two IF stages -- that'll be all
> the gain you need.
>
> The 6EH7 was designed for TV IF service at 40 Mcs. It has the best
> crossmodulation specs of any tube I've seen, as well as a whole bunch
> of gain. I've used a bunch of them in HF RF and IF stages and really
> don't think it can be beaten for updating of a vintage vacuum tube
> design.
>
> Like others, I haven't seen anything indicating the Pullen mixer is
> more than a good low-noise mixer.  But low noise isn't the issue for
> an HF receiver that has an RF amplifier: Good strong-signal
> performance is what's required.  A lower gain dual triode design --
> cathodes in parallel, ditto the plates, grid resistors to ground,
> signal on one grid, LO on the other will do fine.
>
> NOTE HOWEVER that if you make any such change you will have to do
> something to select the harmonic at the LO input grid for bands that
> use harmonic injection. Ted's design (in which the LO was injected
> into the signal grid of the mixer) used the mixer tuned circuit to do
> this.
>
> There are definite advantages to NOT trying to tweak such a
> well-thought-out design. Of course the reason I know it's well thought
> out is that I have tweaked it ... then spent a few days figuring out
> why my 'improvements' didn't work as well as the original.
>
> > It would be interesting to take the designs several years into the
> > future, when still retaining most of the mechanical details outlined
> > in the original series.
>
> With receivers particularly it's important to be careful about
> mechanical redesign.  Been there, learned caution in tweaking THAT,
> too.  Perhaps someone here remembers my very painful (couple weeks?)
> discovery that the cold ends of the HBR coils should return directly
> to the respective rotor contacts on the tuning cap ...
>
> Walt
> KJ4KV
>
>
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