[Drake] TR-4 and TR-3

[Gary Poland]

I believe the TR-3 had to be manually switched from transmit to receive in 
AM, and possibly CW. Its been a while since I have owned one. The TR-3 and 
early TR-4 where pretty much identical otherwise except for the 6JB6's used 
in the TR-4 instead of 12JB6's as with the TR-3. The TR-4's continued to 
evolve with different SSB filters, audio preamp stages, changes in the PA 
cage, T/R relays went to plug types, some changes in IF and Mixer tube 
types, a plug for the 34PNB,  2 dials instead of one, etc.

Gary