Note
QST, Jun 1963, p. 161.
The 399C-1 was an external VFO and speaker for the KWM-2. It lacked the directional coupler, wattmeter, and phone patch found in the 312B-5 station control. It is regarded a quite rare.
The 399C-1 External VFO Unit includes a 70K-2 Oscillator and a permanent magnet speaker. It operates with the KWM-2 Transceiver to provide separate receive and transmit frequencies within the same 200 kHz band when desired. A switch on the front panel provides selection of either oscillator as single frequency control for the station in transceiver service, or selection of one oscillator to control the receiver frequency and the other to control the transmitter frequency. This allows tuning the receiver into the foreign DX bands to listen for DX stations while keeping the transmitter within the legal amateur band. The VFO in the 399C-1 is a 70K-2 Oscillator and is identical to the 70K-2 Oscillator included in the KWM-2.
While Collins Radio Company manufactured a massive number of KWM-2 transceivers over their long production run, the 399C-1 external VFO unit had a very short production window and a small overall production run.
Shortly after the 399C-1 was introduced in late 1959, Collins released the 312B-5 Station Console. The 312B-5 essentially combined the exact same external VFO functionality and speaker with a directional wattmeter (SWR bridge) and a phone patch all into one single, clean cabinet.
Because the 312B-5 offered so much more utility for a complete "S-Line" station setup, it completely overshadowed the standalone 399C-1. Most hams opted to spend the extra money on the full station console rather than buying just the independent VFO and speaker.
As a result, Collins discontinued the 399C-1 early on, leaving behind a relatively small number of units in circulation.
