In my opinion, and the opinions of others of that era, the ARC5 transmitter was not a bad rig at all. I used them on 80 and 40. If you remember, back then the ultimate compliment was to receive an "X" after your RST report, and I got them frequently with those rigs. They were, if powered right, very stable (for that era) and with a clean tone.
The price was right. I got them at the Army-Navy Surplus Store for $3.95 each. That was in 1957, and they were unmarred and unmodified. Of course, $3.95 was two weeks' part time work for me, after school.
I used the receiver as well, though they did not have noise limiting and were very hard on the ears. They were stable, though.
The key to making the transmitter clean was running regulated power supplies at less than max voltages. My ARC5's ran about 40 watts INPUT on CW to the pair of 1625s.
I had the modulator, which I think was the MD3, but i'm not sure. That was a different animal. No matter what I did to it, I never got rid of the hum, and the mic was meant for a carbon input. Tried a couple of times to operate on AM but the signal was really bad, quality wise. I suppose one could fix that, but I wasn't enough interested to try.
The most creative use, and the most professional appearing use, of the ARC 5 was done by a company called Lakeshore. They build the Phasemaster VFO for the CE 20A from the 5 mhz ARC 5. Pretty looking, and highly stable, with built in power supply. The final compartment was where the power supply was, as the finals were completely gone. I ran the CE20A, the Lakeshore Phasemaster VFO and the Johnson Courier amplifier for over a year before I sold it all.
A friend of mine had the 80 and 40 meter TXs in a homemade rack, that was sort of similar to the one used in the military aircraft, that allowed him to have both rigs with filament voltage applied, and merely rotate a switch to change the operating voltages from one unit to the other. Bandswitching! Well, OK, rig switching. I built a very similar unit, not as pretty as his, that had the AC power supply on the back. It was pretty heavy, though. The military version also had a place for the modulator, and two such racks could include the MF and VLF radios as well as the HF ones. But we never found those racks in the surplus stores, and I guess it's because they were installed in the aircraft and scrapped along with the planes.
For the most part I used commercial amateur receivers with my ARC5s, but did try the 80 meter aircraft receiver. Just too noisy to mess with.
Ed, CHOP, W5HTW - Novice 1956, General, 1957, Advanced, 1968, Extra, 1969. Keep the [B][U]amateur[/U][/B] in amateur radio, keep the pros, and Part 90, out of it.