[HBR] HR-10 to HBR project

[Walt Hutchens]

> Excellent plan ...

Thanks Kees.  I hope it turns into something useful!

The dragging dial pointer was due to the plastic dial bulging inward
slightly.  (Clamped to the panel at the ends, no support at the center ...)
I was able to make a clip from a paperclip and epoxy it to the back of the
panel to press the dial back where it belongs.   A more effective solution
will be possible with the new panel since there'll be more space above the
dial.   (Taller front panel required to allow room for 3-1/2" coil forms
with a bit of space above.)

In about an hour yesterday evening I got the set 'sort of' working.
Jumpering the muting connection got the RF-IF stages going and turning all
the controls a few times got some noise in the speaker.   It took 20 minutes
troubleshooting to figure out that the audio detector diode -- one of the
three diodes in the 6BJ7 -- was dead, most likely with a heater-cathode
short.  No spare on hand for that tube so I pulled it and tacked 1N4148's
across the socket.   That made it able to hear signals.

The S-meter is a mess.  It's Shurite-style but open construction with a
blank black stick on face (the scale is on the plastic dial); the needle is
oddly bent; it sits at about 10% with the power off (no sign of a zero
adjust other than realigning the meter body with the dial) and it seems to
hang sometimes.   

I aligned 80M (WAY out, I was hearing CW at around 3800 on the dial) and the
IFTs, (not that bad).   Nothing tricky about alignment -- just stick a
plastic hex tuning tool in the coils and twist, though the front end must be
done from below.   (And according to reviewers, is detuned when you put the
bottom plate on the chassis ...)

Hooking up a good antenna I found it will hear signals, although it's sure
no ball of fire -- the Long SLOW receiver was copying the same stations
without an antenna!   In fairness, most tubes ARE original and although they
don't look 'high hours,' I really don't know.   And after 50 years,
resistors may have changed value, leading to incorrect voltages.

Those problems the various reviewers talked about?  They're all there:  AGC
operation moves the LO, the BFO is wimpy and tends to lock with carriers,
the audio's not much.   These issues aren't as serious when treating the
HR-10 as a 1940's receiver, running the audio full up and controlling volume
with the RF gain control per the manual.

Some of the design stuff is bush league.   Not only do the filaments return
through the chassis, but the filament winding of the transformer is grounded
to one of the twist-lok lugs on the filter cap.   So ~3.5 amps AC is going
through the contact between that lug and its slot in the chassis: Any
voltage there is in series with all the plate supply voltages.   But they
saved a solder lug and a sentence in the assembly manual.

While there's quite a bit of cleverness -- $0.25 worth of parts doing a job
you'd expect to require 20 times that and doing it well -- I plain don't
believe this is the best that could be done with this number of dollars in
the 1960 time frame.   Among other things, the W6TC sets were already out
there as examples of what was possible.

The half lattice crystal filter sort of works -- smooth peak ~2 kcs wide --
but there seems to be a spurious response that (according to the S-meter) is
about 35 db down, about 25 kcs above the dial setting.   (That would be 25
kcs LOW at the IF, if my coffee is now functioning ...)  This needs further
investigation -- it has the sound of a bad crystal, and when I checked them
in my test oscillator one was on frequency and the other wouldn't go.

The screwy S-meter complicates testing: Probably that ought to be a
priority.  This S-meter is in the HV line to the 2nd IF stage so even more
than usually, screwdrivers need to be kept out of that area when the set is
on. 

The three-section filter cap seems to be okay.   The set is decently clean,
has only the obligatory dots of rust on the power transformer, and the while
the wiring job isn't great, it's not full of soldering iron scars, either.
Nearly all of the small parts and on-socket wiring will be replaced as the
HR-10 to HBR project proceeds, so that will get tidied up.

The power transformer is adequate, getting just slightly warm to the touch
after an hour of operation.

NICE looking set when turned on -- dial is nicely illuminated, easy to read,
and works well.  Tuning rate is quicker than ideal but tolerable, even for
SSB. Ergonomics is excellent, considering the price range.  Mate this with
the performance of an HBR design ... yeah, I think that could be a winner.

The slide switches will be replaced.  The common cold of the Heathkit world
those things are ...

I can either start at the audio and work backward (usual approach with
receiver construction) or do the plug in coils and other front end stuff
first.   At the moment I'm thinking 'front end first' because that's the
biggest reconstruction mess and replacing the front panel needs to be done
at the same time.   More front end gain will make the other work easier.

AND I think I see a way to lay out the front end so everything will fit.

Today: Order panel, meter fix, couple photos.   New tubes -- most of them
will change -- are on  hand or on the way.  Continue work on the Long SLOW
... project.   You would not be wrong to guess that the BFO needs more than
just a temp compensating capacitor.

Walt 
KJ4KV