[Amps] INTERFACING IC-746 with Amp Supply LA-1000 amp

[Han Higasa]

gm Roger

It would be a simple matter if the amp is using a T-R control by
grounding a cold end of a relay coil; maybe THP and Henry do.
I am also using similar scheme in my hb linear amp.

For once in my life I am reading  an Alpha 87A manual.
They said: The voltage at the relay jack is 5V at 1mA;
this is acceptable for most modern transceivers.

Maybe the amp will not allow residual voltage such as
0.7 V or 1 V when the keying (T-R) line is logic L for transmission.
If it is true directly connecting the "relay jack" to the ground will work;
but with one silicon diode it will not work.

I do not have schematic diagrams of  IC-746 or -756PRO
but I presume they have a protection diode in series of "send" jack.
If raw make/break contacts have been connected 78A should work.

Alternatively you can also use pin 3 of ACC1/ACC2 connectors.
It is a bi-directional pin to control - or controlled by - aux devices.
It will work as an open-collector (active L) when 756 is in transmission.
If pin 3 is grounded by aux devices, 756 will be in transmission mode.

Use one low forward voltage Schottky Barrier Diode in series to pin 3
and "relay jack" and check if 87A will work with your 756.
Make sure to connect a cathode of the diode to pin 3; an anode to the
"relay jack"; and connect a 0.01 uF bypass capacitor in  parallel to the
diode.

Using pin 3 (SEND), pin 7 (13.8V) and pin 2 (GND) , SBDs and transistors
I have made a stand-by expansion box with antenna-relay control for
local friends.

73, de Han JE1BMJ