Conversion to Amateur Use

The T-368 requires little in the way of conversion for amateur use. In fact, the T/R relay is built right into the unit! The antenna and receiver connections are located on the left hand rear of the unit. The receiver connection utilizes the same “C” type connector as the R-390A. Shaped like a large BNC unit, male “C” connectors are available, but not common. This connector can easily be switched over to a type “N”, or SO-239 unit. The antenna connection is the standard miliatry “N” type and should present no problem.

Line Power

The T-3 runs off 110-120VAC line current. A stiff service of at least 20 amps is required for the unit to reach full power.

The stock 2 wire line cord and socket should be replaced with a heavy 3 wire grounded system for safety reasons. Be certain to leave the 2 blade connector, the one closer to the center of the unit, in place. Removal of this plug disables the HV circuit and the unit will not transmit.

Audio

The mic connector on the front uses a common military connector. The number is a U77 if I recall correctly. I use terminal pin “C” for my audio input. For front panel PTT switching use pin “F”. The ground connection is pin “D”. It has been suggested that this connector be removed and replaced with a XLR unit. However, I have had good results using this connector, and even use it with T-3 #1 with the broadcast audio chain.

The stock T-3 sounds quite good on the D-104, but be sure to remove the bias voltage present on the microphone connector, it was used with the stock carbon microphone. It has been reported that the mic input line from the rear multi-pin connector J12 can cause hum in the transmit audio, but I have never experienced this. However, I would suggest that audio input be feed into the front mic connector rather than the rear socket.

T/R Switching and Receiver Muting

Although the unit can be put into transmit via the front panel switch, remote T/R switching can be accomplished via the rear control socket J12. Pin “A” of J12 serves as the PTT contact. To put the unit in the transmit mode, just drive pin “A” to ground. For receiver muting, use Pin “J” of remote control socket J12. When the T-3 is in the transmit mode pin “J” goes to ground. I use this directly with my R-390A for transmit receive audio muting.

J12 Pinout
Application
A PTT
B Plate Relay
C Plate Relay
D 600 Ohm Audio Input
E Shield Ground for Audio Input
F Carbon Microphone Input (13+ Bias)
H Sidetone Output
J Receiver Muting

Casters

As the T-368 was typically mounted on shock mounts and metal beams it is a good idea to install at least 4 wheels to allow the unit to roll about. Ideally wheels with some provision for locking should be used. Be certain to select wheels that will carry the T-3s 700+ lbs. of weight. Grainger sells just such a caster unit. The part number is 1G042, and has a retail price of $9.26 each. The 24 hour telephone number for Grainger is 1-800-225-5994.

Lighting the VFO

The VFO dial on the T-3s exciter unit is not backlit, making it difficult to read in dark or low light conditions. It is a simple matter to remove the exciter unit from the RF deck and install 2 small light bulbs behind the VFO dial “shutter”. Power for the bulbs can be taken off the filament voltage used with the exciter tubes. When selecting light bulbs, look for one small enough to fit between the “shutters” of the VFO dial.