I'm curious as to why the channel selector runs
1,2,3,4,5,6,A,B,C,D,E,F. Why numerals 1-6, and then letters A-F?

Raymond-

I had the HR-2A back in the 70s. It was one of the early solid-state Two Meter
rigs. I don't think I have the exact information you need, but thought I would
pass along some recollections.

1. The transmit crystals are in the 6 MHz range. The later HR-2B model had a
multiplier chain with different multiplier ratios, using 8 MHz crystals in an
attempt to increase drive. It seems that there is an instability that causes
out-of-band spurs when drive isn't high enough. Unfortunately there is also an
SWR protection circuit that reduces drive if SWR is high. Naturally the
out-of-band spurs will have higher SWR when loaded by an antenna tuned to Two
Meters, but not when loaded by a dummy load in the shop! (This isn't normally
a problem with the HR-2, but is extremely serious with the Six Meter version,
HR-6.)

2. There was a modification kit, maybe offered by another company, that added
six additional crystal sockets and trimmer capacitors for the transmitter, to
enable the full twelve channel transmit capability. The channel selector
switch already has the terminals for the additional crystals.

3. One weak component is the channel selector switch. It develops bad
contacts after much use. I recall using mine almost like a scanner, and wore
out two sets of switches. The switch wafers can be replaced without replacing
the other mechanical switch components, although disassembly is necessary.

4. The circuit boards are very similar or nearly identical to an early version
of the Regency BTH-201 commercial VHF High-Band transceiver. I believe the
commercial version may have used a higher-powered transistor. It used
push-buttons rather than a rotary switch for versions with more than one
frequency. (The HR-6 is similar to the commercial BTL-301.)

5. Receiver sensitivity is not very good by today's standards. Back then,
there were at least a couple dual-gate mosfet preamplifier kits offered by
other companies. They increased sensitivity from around 0.35 microvolts to
around 0.2. Of course the radio becomes more susceptible to intermodulation
interference when the preamp is used.

6. As far as I can tell, the company that was Regency was split, with the
scanner portion going to Uniden and the commercial two-way radio portion
becoming RELM, located in Melbourne, Florida. I doubt they can provide much
information about the HR-2A, but it might still be possible to obtain service
information about the commercial BTH (and BTL) series transceivers.

7. In recent years I have heard of several HR-2/2A/2B/2S/212 radios being used
on packet. They apparently work OK in that application. The only problem I
can think of, is knocking the audio level down far enough to keep from
over-driving the microphone circuit. The HR-2/2A/2B/2S/212/6 used a high
impedance ceramic microphone element.

I spent a LOT of hours working on the HR-2A (and HR-6). If you have any
specific questions, I might be able to recall something that would help.

73, Fred, K4DII