[HBR] Heath HR10B

[Walt Hutchens]

Steve said:

> It is in Jan 2012, Nov 2011, and Oct 2011..Walt if you can find your notes
> and a schematic that would be very helpful...

The notes, such as they are, will be found. No schematic exists and I
wouldn't recommend the design to anyone but myself; there are 'issues'
that -- even after several models -- still often take me a week or
three to sort out.

What I suggest is building an HBR-8, -11, or -13 on that chassis. THAT
circuit is designed to be easy to get working. I'll see if I have
those schematics and can suggest which maps best to the chassis.

The HR-10 is an excellent foundation: Virtually everything is there to
build an only modestly modified HBR (you would use a single
intermediate frequency of about 1680 kcs set by the half-lattice
filter of the HR-10) so you are spared finding the parts, trying to
get them to work together, and most of the metalwork. I wouldn't say
the one I built is inferior to the nearly identical receiver I built
using an Eddystone dial in any practical way.

The problems in the circuit I use come mainly from the use of plate
detectors for both audio and AVC and using the AM detector to also
serve as a product detector. It works fine but it's very subject to
gas and heater-cathode leakage and with most tubes being ~50 years old
now, it's problematic to get going. The good tubes are still fine, but
the bad ones will give you more fits than you want when used in this
circuit.

The AGC circuit is higher resistance than the usual diode circuit and
a gassy tube in any AGC'd stage really messes things up. But when it
works it's good enough that no separate RF or IF gain control is
needed -- there's an AGC threshold control and an audio gain control
and that's it. It holds any round table to tolerable audio levels and
doesn't clip the beginning of sentences.

I borrowed the Collins two-time constant AGC scheme. The other ideas
came from the Yaesu FT-200, sold in the US as the Tempo-One. I changed
virtually all the details but the ideas are Yaesu's.

Additional issue: It is usually necessary to neutralize the AGC
detector, that is, feed in a bit of BFO signal with the reverse phase
in order to prevent the BFO from kicking the S-meter up. Yaesu had
this problem and it took me forever to figure out exactly how that
worked from the fact of a 'gimmick' across the tube socket. It's shown
on the diagram but there's no clue what it does.

When you draw the circuit the right way it jumps right out at you, but
that took me a while the first time -- the circuit in the manual was
laid out for draftsman convenience.

In order to do the neutralization trick you need both phases of BFO
sig which as I recall changed the BFO circuit -- I'll have to look at
the set to refresh my memory.

Use of high gain detectors allows keeping the signals small through
the IFs which means that sharp-cutoff IF tubes are ok. This is
effectively amplified AGC but those circuits usually add the gain at
the IF -- an extra IF stage drives the AGC -- so you have to deal with
signal pickup and stability issues. Using a higher gain (i.e. plate)
detector puts the gain (effectively) at DC so there are only the
issues of a single tube DC amp.

Walt
KJ4KV