[R-390]R-390/URR Questions (Green R_290)

[Mike Crawford]

The plot thickens.

Upon close examination it appears the front panel has been refinished. Where 
the sickly green paint has been chipped you can see gray paint behind it. 
Also the rear of the panel is the usual gray.

It is an etched panel and the engraving has been filled very nicely. It 
does, however, have stickers on the panel which were applied after the 
refinishing that indicate it was still in govt service.

On the rear panel are dymo labels which state the following:

MB.4.3.1
MB.4.4.2
31R1.2URR.154
31R1.2URR.506
31R1.2URR.507

I assume these refer to approved modifications which have been applied to 
the radio. I know that TO 31R1.2URR.154 is one of the Air Force tech manuals 
for the radio but have no idea about 506 and 507. Can someone translate? I 
do have changes 1,2,3 for the 154.

For those who are interested it is a Collins, Order Number 14214-PH-51-93 
SN: 1974. I did notice it has a Motorola power supply.

Thanks for all the help.
Mike