Nice, Is this actually a Collins unit or one of the later ones. My R390A is a 1967 EAC unit which means it was built by Hammarlund. what have they done for the 3TF7 ballast tube. If it is still there you will want to replace it with it's solid state replacement as I have done on my R390A much better. I have always got a kick out of the Veeder-Root mechanical display. Here is the download to the best tech manual for your R390A the Y2K manual. It is free.
http://hilltoparmyradios.com/1948_R390A-Y2K-Release-1.PDF
Most all of the R390/URR's I have seen have been Collins manufactured, while most of the R-390A/URR's have been made by other contractors, the A in the rack in the shack is an EAC model.
If you really want to be astonished in the back load for the diode out binding posts through an isolation transformer run that into an good audio amp The R390A will sound like an old console radio.
And, because of the gentler slopes of the R-390/URR's LC tuned circuit filters and less ripple the straight 390 has a bit of an edge over the mechanical filtered version here, too.
RickB, I remember Ozona Bob, his Viking 1 and his 30+ minute key down rag chews. Now that I have retired I am going to put the My Viking 1 transmitter on the work bench and get it going again. I will match it up with my very most favourite receiver the R388/URR.
That was the standard operating practice for our group back then...i.e., you make a transmission...not just a wham-bam-thank-you-ma'am quickie, but a real transmission of substantial content....which is still quite different from 99% of the SSB contacts I've had in all my years as a Ham...
Bill Ross, K5LLK (SK) and I used to go to the Hamfests out in Midland and Odessa so we'd always stop by to visit with Bob and go have a bite to eat with him at a restaurant he liked...we'd visit his "shack" and see all the gear and his turnstile 75m antenna up on the Black Diamond telephone poles...
I still try to get in on the Collins Collectors Net on Sundays, 14.263 MHz, when conditions are decent and mostly to exercise my S-line or KWM-2/30L-1, but that's about all the Hamming I do now...except maybe for 10m FM repeaters with my FT-990/Alpha 76A....worked a few European stations through the New York repeater recently...
I've also got an R-388 out in the garage that needs it's VFO rebuilt...never got around to it since the 51J-4 replaced it in the rack...
But, I really, really miss the "good ole days" of AM'ing and my friends...my Barker and Williamson BC-610-I was gone through by John Mohn before I got it so that it has a 50 Ohm SO-239 antenna output alleviating the need to have the companion antenna matching unit, man, that guy was a freaking RF genius...he also worked out at Southwest Research Institute in the RF labs....the last time I saw him he was in a nursing home and didn't hardly remember who I was or even know why he wasn't at home...he passed several years ago, now....