[HBR] HR-10 to HBR project

[Walt Hutchens]

Tom said:
> An old trick from the Navy is to take a tiny drop of liquid soap - rub it
> all over the plastic face (edges too), the polish it off with a clean skivvy
> shirt (T-shirt to you civilians).  The soap reduces the surface tension, and
> eliminates static effects - it may not fix the meter, but it's one less
> condition you must deal with.

Ah yes ... static can sometimes hold a meter needle in a strange place.
Good one ...

'Skivvy shirt' still spoken here, Tom, although it has been a few years!

> The 1680.7 kcs crystal is bad.

And in poking around looking for another, I've found that others have also
run into this problem.

Sudden flash of insight: This is likely the consequence of transmit RF
getting into the receiver front end via a bad TR switching scheme or use of
a separate antenna for receiving without some provision for killing it on
transmit.   

Who built these radios?  Not the experienced ham who would have a shack
already set up to take care of this issue, but a Novice who would likely
have no clue.   Nor does the manual give warning.

These receivers have NO protection -- not even the neon lamp on the antenna
post of the lowly command receiver.  The modern plated crystals are
generally spec'd for 1 mW maximum drive levels and it's easy to imagine a
signal 20 dB greater than that coming out of the mixer on a set like this
one.  

The mixer isn't killed on standby.  So whatever can reach the mixer grid
will be converted and get into the filter and the only built in protection
would be the open cathode of the RF stage.   THAT, at least, probably can be
fixed.     

Moving the sharp filter closer to the antenna makes for a better receiver
but it means the filter is exposed to more danger.   This may be a place for
a modern solid state protective device.

> The next thing is an IEC C14 connector for the line cord ...

Done.  

The IEC C14 is the receptacle into which the power cord plugs on most
desktop computers.   I've gotten to using them on just about everything I
build or modify because it's just a lot more convenient to be able to
disconnect the line cord at the radio.   Also you can get these receptacles
with a built-in filter -- handy when half the stuff in  your house is
pumping trash back into the line.

I will also replace the RCA phono plug used for the antenna with a BNC
connector.   Yeah, RCA connectors work but ... life's too short.

> then, I think, starting on the front end revisions.

The first step there is to relocate the calibrate and antenna trimmer
capacitors so there'll be room for the antenna and mixer coils.   After
that, it's into the front end with the wire cutters and nut driver ...
"Strip to a bare chassis and lay out new holes as follows ..."   However it
shouldn't take more than a couple of days to get the major chassis work
done.  

I will be able to leave the original panel in place until the front end is
wired and tested.   That's good, because 1/3 of the chassis and four tubes
is a lot to have open for revision at one time and the panel is another big
mess to do -- dial cord, four switches, and assorted other controls,
tiptoeing around that meter, plus making, painting (etc.) the new panel.

Working with this little set the last couple of days I've come to appreciate
something that I missed at first:  It FEELS right.   It's heavy enough, it's
mechanically rigid, and the tuning has a solid feeling.  There's no play
worth mentioning in the tuning knob and darn little backlash.   There's a
small flywheel on the tuning knob shaft that contributes to a feeling of
'serious radio here.'

Interesting ... Heath did only 'okay' radio engineering -- they needed the
engineering equivalent of an editor, to look at items like the HR-10 and say
"Not good enough."  But the marketing aspects of design -- what impression
does the set make? -- on the HR-10, they got that right.

The 'Long SLOW ...' project is in a slow phase again, back to temp
compensation for the BFO.   Unfortunately I had to remove a couple of turns
from the coil, meaning a couple of dabs of clear nail polish, meaning that
drift measurements are meaningless for a couple of days.

Walt
KJ4KV