Signal Corps AM-1249/U audio amp Signal Corps AM-1249/U audio amplifier
This Signal Corps audio amplifier was found at a hamfest. The unit was sold with just the 12AX7 tube. The others, a 5Y3 rectifier and the push/pull 6V6 pair, were missing. It was in very good cosmetic condition, just needing a cleaning.
The manufacturer was Telectro Industries and the order date was 1954. The serial number on this example is 19. I looked for any references to this model on the web but could not find any. The lack of references and low serial number make me wonder how many were made. The amp is rugged and quality as one might expect from the need to meet military specifications. The output transformer markings show the circuit to be ultralinear. 
As shown below, it matches paint and rack-mount dimensions of the R-390 and makes a decent companion piece for that or other military radio such as the SP-600, connected to the receiver's line level audio. The amp has phone jacks for headphones and for an external speaker. The onboard speaker was made by Utah.The Signal Corps AM-1249/U audio amp matches the rack space of the R-390 receiver.
Troubleshooting
I replaced the missing tubes and fuse and did a slow power up of the amp. It turned out to be in very good condition and not in need of repair other than the usual cleaning of the tube pins, volume pot and switches. The power connector was a military twist lock. I opted to replace it with a three prong IEC connector pulled from a defunct computer power supply. That conversion is easily reversible with no cosmetic changes.
A Signal Corps BC-1031-C Panoramic Adapter was the previous item on the bench.