The M37 Truck came with a radio antenna, and I thought it would be nice to be able to use that. My overall goal was to make use of the equipment that came with the truck (antenna mount and LS-166 speaker), have a useable method of communication while in the truck, and have the radio appear to be ‘period correct’ (meaning the equipment would look like it would be in use in the 1950’s era). I didn’t want to ruin restorable equipment while doing this.

The actual antenna mount is an AB-15 base on AB-243 mount with antenna elements, but these are tuned for 30-90MHz, not 144-148MHz used by the 2m amateur radio I prefer to use. It is possible to use a working AN/PRC-8/9/10 on amateur radio (on 6m) but there isn’t a lot of activity there that I have found, although solar activity dictates this in cycles of which we are in a bad period. I also could have used CB but having monitored that over the last couple years in my area, I have not found anything interesting on it. That leaves 2m, which in my area is active and interesting to use. I also had an Icom 880H radio that hasn’t seen much use since I sold the car that it was in previously. Having the 880H as the working radio, I just needed the shell, and the AN/PRC-8/9/10 series of radios had it all – it looks great, is of the correct time period, and is large enough to contain the 880H.

Fair Radio Sales	Fair Radio Sales – Electronic Military and Industrial Surplus	Provided the AN/PRC-9 and hand mike
AB5N	HM-133 | ab5n-mic-upgrades (7000mic.com)	Provided components and assistance
Tiny Micros	Icom HM-98/HM-133 Internals – Wiki (tinymicros.com)	Specifics on the HM-133 (Icom) hand mike
N6CC	PRC-10 Infantry Radio | N6CC	Information on the PRC-8/9/10 series
K4CHE	PRC-10 Info Section 1 (k4che.com)	Information on the PRC-8/9/10 series – Details on restoring an original set
PRC68.com	H-33 Handset (prc68.com)	Details on the H-33 hand mike

Painting may not be needed depending on the condition of the set, but the example I had needed it. The paint must be thin to look correct. Painting of the raised letters worked with a stiff rubber applicator while painting upside down to discourage paint wicking. Paint that flows outside of where it is supposed to go can be gently removed with magnifier, an exacto, and patience after it dries. I used POR-15 as primer since I had some for another project, but it appears to adhere quite tenaciously and should be a good choice, as long as it is applied thinly.

For the electronics, I couldn’t escape using the Icom HM-133 hand mike circuit board since it uses bitstreams to code PTT on and off. The PTT trigger is very sensitive and would key up when connecting any kind of mechanical switch which is why I used a photo isolating switch for it. The HM-133 required de soldering of the PTT switch and the microphone element. I soldered wire leads from those holes to their destinations and there is little room to work with, but it worked. The HM-133 is in a block of foam cut to keep it in place with a plastic cover on it to prevent shorting. Schematics in the previous post.

I was able to preserve the function of the original on/off rotary switch as an on/off switch for the PTT and display LEDs, but the Icom 880H control head still powers the 880H on/off. The volume and squelch of the original I could not find a straightforward method of adapting these, but it might be possible later. The tuning knob and display of the original still works visually but had no effect on the radio operation. It does look nice cleaned up and illuminated, however.

Internal wiring is a balancing act of having enough to disassemble, but not so much as to no longer fit. I oriented it with the 880H fan facing the rear so hot air could leave via a vent hole I cut in the PRC-9 battery box. It would have been more convenient for wiring if it was the other way, but it would have no place to vent. This vent and the hole for external speaker, power, and 880H control head line is concealed by the (very handy) swing out feet on the battery box.

When I get the truck back ill find a way to mount it in there but finding references on installing radios in the M37 are scarce. I find some reference to mounting in the truck bed, but I’ll try to adapt something to the cab.