[Milsurplus] aircraft transmitter & dynamotor

[Morrow, Michael A.]

> Key B+ for CW & on key-up, dump dyno into a 4000 ohm 50 watt=20
> resistor. =20
>=20
> Further this 4K resistor is a re-invention of the wheel since=20
> resistor 143in the unobtanium system junction box appears to
> do the same thing.

Marty,

Resistor 143 in the TM-AH-172 junction box is only about 10 ohms.  I've
never found an SCR-183 manual parts list with the "official" value, and
the one in my TM-AH-172 has indistinct colors.  I had to measure the
value.  It appears to be about a two-watt resistor, which is consistent
with its low ohm value.  It is in series with the dynamotor unit's
choke-filtered B+ output, which junction box TR relay 153 switches to
either supply B+ to the all receiver stages except audio output, or
supply B+ to all transmitter stages.

The receiver also gets an unswitched higher B+ through dynamotor unit
resistor 146, which is applied to the audio output stage.

The relay-switched receiver B+ is routed back to the dynamotor unit and
passed through dropping resistor 152 before being sent to the receiver.

I forget what the manual says the function of resistor 143 is, but it
can't really be all that essential.

It's always seemed odd to me that an equivalent junction box wasn't made
for the 24 vdc SCR-283 system.  The voltage only matters because of the
TR relay coil in the junction box.

73,
Mike / KK5F