EB5AGV's R-390A Hints

Keep them glowing!

This page is a recollection of useful information about the R-390A. Most of it comes from the Boatanchors List (thanks to all anonymous contributors!). I have been collecting it since I became interested in BAs. The R-390A attracted from the beginning my attention...

Manuals for R-390A

Army manuals

TM 11-5820-358-10
'Operator's Manual, Radio Receiver R-390A/URR'
16 January 1961 (Change 1: ?, Change 2: 15 January 1965, Change 3: 25 April 1974)

TM 11-5820-358-20
'Organizational Maintenance Manual, Radio Receiver R-390A/URR'
(Air Force number: TO 31R1-2URR-442)

TM 11-5820-358-34P
'Direct Support and General Support Maintenance Repair Parts and Special Tools Lists, Radio Receiver R-390A/URR'
February 1972 (Supersedes TM 11-5820-358-35P, 20 March 1962, including all changes).

TM 11-5820-358-35
'Field and Depot Maintenance Manual, Radio Receiver R-390A/URR'
8 December 1961 (Changes 1 and 2 at least were issued. It, together with the Operator's Manual above, supersedes TM 11-856A, 20 January 1956 including changes 1-6.


'Operator's Manual': It is a very simple one.

'Organizational Maintenance Manual': 38 pages. Tells how to remove and replace sub-chassis. Brief descriptions of trouble shooting.

'Direct Support ... Parts and Special Tools List': 160 pages of lists of parts. Mostly useless except for 24 pages of very good photos showing parts locations.

'Field and Depot Maintenance Manual': 189 pages. Contains theory, detailed trouble shooting, inspection and calibration / alignment instructions, voltage and resistance diagrams, parts location illustrations and, the most important, schematics. This is the recommended Army manual to have.

Navy manuals

NAVSHIPS 0967-063-2010
'Operation, Maintenance and Installation Instructions with Part List, Radio Receiver R-390A/URR'
15 April 1970 (supersedes NAVSHIPS 93053 Vols I, II and III and NAVSHIPS 93053.42A).
Manual prepared by Philco-Ford Corp, Communication and Technical Services Division under Contract No. N00189-67-C-0959


'Operation, Maintenance and ... ': about 250 pages, with lots of detailed schematics and pictures. I have an original and the pictures quality is excellent. It includes the following chapters:

Chapter 1: General Information
Chapter 2: Operation
Chapter 3: Functional Description
Chapter 4: Scheduled Maintenance
Chapter 5: Troubleshooting
Chapter 6: Corrective Maintenance
Chapter 7: Parts List
Chapter 8: Installation

Chapters 5 and 6 are very detailed.

R390-A FAQs

Cosmos PTO Alignment (by Bill VanAlstyne, N6FN)

I adjusted the end-point slug with the PTO removed from the R-390A chassis and hooked up to a frequency counter. This procedure worked fine, and I was able to correct for my approximately 1% (10 kHz in 1 MHz) PTO/dial error. I put a paper template under the shaft coupler plate, and that worked accurately enough to get it within +/- 100 Hz on all 100 kHz calibration points.

Now, as far as adjusting the little linearization compensators (of which there appears to be one for each 25 kHz of tuning range), I found I really couldn't get an accurate enough position measurement with my paper template method except on a repeating 360-degree basis -- i.e., a single calibration mark per rotation for each 100 kHz point.

To accurately adjust the linearization compensators at *each* 25 kHz point, one would need to make an adjustment jig with a large (or geared) substitute dial mechanism -- or figure out how to make the adjustments with the PTO installed in the chassis. Right now, I'm figuring to work on the latter approach. It appears it will require some specialized tweaking / viewing tool(s). Roy Morgan and I are collaborating (cross-country) on this dubious endeavor. Any and all advice from other intrepid souls who have "been there and done that" is eagerly solicited.

In any case, at the moment I have probably +/- 200 Hz accuracy anywhere along the 1 MHz range, with +/- 100 Hz accuracy at the 100 kHz cal points. Not bad... but not as good as it could be. This was just a first attempt to figure out how it worked and what might be done.

Electrical/thermal stability of this PTO appears excellent, BTW, especially with the oven running. So far, I would give the Cosmos PTO pretty good marks, both in terms of design and implementation.

R-390A PTO Alignment (by Tom Marcotte, N5OFF)

I simply use the disk on the Oldham coupler as a guide, and make pencil marks on the disk and frame to turn the shaft exactly 10 turns, no paper templates or anything like that. Here is the procedure w/o the compensating stack adjustments.

1) Hook up freq counter to PTO output.

2) Make note of output in KHz for a 10 turn input (ex 991 KHz for exactly 10 turns).

3) Turn the adjusting screw 1/2 turn or so and make note of the amount and direction.

4) Erase old pencil marks and make new ones (what was a convenient mark will now move to a new spot).

5) GOTO 2 until output is exactly 1000 KHz for exactly 10 turns from the spec. start and stop outputs. For example, the R-390A PTO will output from 3455 to 2455 KHz in exactly 10 clockwise turns.

PS: I leave the ovens OFF all of the time. The PTO oven will just cook the lubricant out of the PTO. Leave it off. Let the rig warm up well before beginning PTO work, and do the work at room temp (24 degrees or so).

Does 3TF7 ballast mod change alignment? (by Chuck Rippel, WA4HHG)

Q: I'm going to do the 12BA6 mod and was wondering if anything will change or is an alignment necessary for the R390A.

A: No need to do it unless you have a bad ballast tube and cannot locate another. In theory, the only alignments which might charge are:

PTO endpoints
PTO linearity
1st XTAL oscillator output

In any case, if you were to replace V401 and V701, you'd want to at least check these aligments.

R-390A Diode Load How To (by Tom Marcotte, N5OFF)

I got a couple of notes asking to elaborate on the use of the diode load tap on the back of the R-725 (390/390A) for audio use.

The diode load screws (two) have a jumper connecting them in normal use, and they are found on the back of the set. This is actually the detector signal, brought out just before the noise limiter, and also before the line and local audio amps. There is no audio filtering here, so what you get is what you get.

One can connect the signal to an outboard audio amp via a capacitor. I used a 22uF connected to the diode load jumper. From here I used the center conductor of a shielded audio cable to feed an amp, the shield being connected to the set ground.

The signal level coming off of the diode load is about right to drive the outboard amp on my set, with the volume control on the amp set at about 25% I get a room full of sound.

In normal operation, I had a slight hum, probably coming from somewhere in the audio deck. Now, hum gone. The amp I am using has nice speakers and an equalizer.

Caveat... if you alignment is poor on your 390X, then your diode load signal will be low...but your audio would be low anyway then with the regular audio deck.

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