Info on the 4 pin connectors that were used for the Drake 2-AC 100Khz
crystal callibrator module and the Drake 2-BQ Q Multiplier/Speaker:

The original Socket is a CINCH #2675, the mating Plug is a CINCH #5AB2,
EBY (Philadelphia) also made a competible plug/socket.
The pins measure 0.098" x 0.325".

The Cinch 5AB2 plug was often used as an A/B battery connector in
broadcast receivers.  It was also used in automotive 8-track cassette
players.

There is a compatible 5-pin connector, but the center pin must be
carefully removed to avoid damaging the connector.