[Milsurplus] Seen a TBO before?

[Mike Morrow]

I recently acquired a manual for a set that was previously unknown to me, the USN TBO and TBO-1.

This turns out to be the immediate ancestor to the TBX-series.  The main difference seems to be that the transmitter has only one MO band, covering 2000 to 3500 kc.  Early TBX units covered 2000 to 4525 kc, and later TBX units covered 2000 to 5800 kc, each in two bands on transmit.  The TBO receiver mechanically and electrically is almost identical to the early TBX receiver.  All TBO and TBX sets received 2000 to 8000 kc in three bands.

The TBO lacks the NET switch that is on later TBX units, and has three dummy sockets for spare tubes, including the 837.  Some of the under-chassis components are arranged differently.  The set was made by GE, and the earliest referenced contract date is 1935.  From a few feet away, you can't tell that you aren't looking at a common TBX unit.  I never knew that the TBX design was based on a mid-1930s GE design.

I guess the USN folks specifying the TBO/TBX frequency ranges and the Signal Corps folks specifying the SCR-284 frequency range (3800 to 5800 kc) didn't see value to having much inter-service compatibility. 

Mike / KK5F