HR-10/B

[Richard H. Arland]

I have owned three of these receivers over the years. My first HR-10 was
my Novice receiver for a year. Had many great QSOs with it, although now
I wonder how I ever managed!

My current HR-10B is a very nice piece. There were a few things I tried
to get its performance up a bit. None of these are original ideas and
they have been published before.

1. Stabilize the B+: My line voltage is high and I noticed that the B+,
measured at the junction of R44 (1.5K 10 W), C56 and R43 (22K 1/2 watt)
was 135.8 Volts. It should be roughly 125 Volts. I replaced R33 with a
3.3K 10 W and added two 5 W zener diodes in series (a 120 V and a 5V)
from the junction of R44/R43 & C56 to ground (anode to ground). This
yields a nice stable  125 V B+ line.

2. Stabilize the B+ voltage on the BFO: Replace R39 (68K 1/2 W) with a
33K 1W and add a 30 V 5 W zener from pin 1 of V4B to ground (anode to
ground). This places the plate of V4B at 30 volts and helps keep the BFO
from drifting.

3. Increase BFO injection: most HR-10s suffer from low BFO injection.
There are a couple of solutions. First is to take a couple of 1" pieces
of solid covered hook up wire, solder one to pin 9 of V4B and the other
one to pin 2 of V4A. Move the pieces of wire together to increase the
capacitive coupling of the BFO to the 2nd IF Amp/Mixer (V4B a 6EA8).
This is the "gimmick" method of coupling the BFO signal into the IF.
Alternatively, you could try a couple of small disc caps, say somewhere
between 2 and 5 pf, to do the same thing. Just hook the cap from pin 9
of V4B to pin 2 of V4A. You probably have to play with this to get it
just right.

3. Reduce the gain of V6B, the audio output stage: remove C38 (10mf @
25V Electrolytic). This is the same as removing an emitter resistor from
a common emitter transistor amp. It reduces stage gain and efficiency. I
tried it by snipping the wire and then using a clip lead to alternately
connect and disconnect C38. I find that my HR-10B sounds better with C38
disconnected. Personal taste here.

I am sure there are other things you can do to this fine example of a
Novice receiver of the 1960s. Check out Mike Bryce's Heathkit Shop web
site for further details.

73 Rich K7SZ

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