RadioBanter - View Single Post - Drake TR-4C -- need advice -- PTT not working

July 10th 04, 03:50 AM

(K5DH) wrote in message ...
In article , says...

In article ,
K5DH wrote:
I recently bought a Drake TR-4C / RV-4C / AC-4 station
which came from an estate. The gear is nice and clean
and appears to be 100% stock.

After I rebuilt the power supply and replaced a couple
of tubes, the station is operational with the exception
that I have no push-to-talk (PTT). VOX works fine on CW
and SSB. I replaced the 6EV7 tube, and that didn't help.
I tried two different microphones and got the same result
with both of them. Both mics work fine with my B-Line,
so it's not a mic wiring or switching problem. Before I
dive in with a voltmeter, does anyone have any suggestions
on what may be wrong, perhaps based on personal experience?
And yes, I'm aware that the CW key must either be closed
or unplugged for PTT to function.

If you are set for SSB operation and plug a key in, does
closing the key transmit?

Nope. Closing the key yields a momentary click of the T/R
relay and that's it.

I would start looking at the CW key jack and the microphone
jack and the associated wiring.
--scott

Already looked at the wiring. Didn't see anything wrong with
it. No evidence it's ever been tampered with, either.

Dean
Hello Dean, I am presently restoring a TR4 and just finished checking
out the mic circuit..On the side of the TR4 you find the first jack
is phones, second one is mic,take a clip lead and short the mic
connector key wire(tip of connector) to ground,it should key up the
relay...tube V19B 6EV7 is Vox tube,it works for Vox and PTT,if vox
works PTT should work also...look at first grid of V19,pin 2,move to
left to junction of R142,R105 and R108 ,key this junction to ground
with test lead,relay should close..Also notice the three resistors
connected to pin 2 are high value 1M, 3.3 M & 6.8 M..Hi value
resistors will always go bad with age,take them loose and check them
with good meter,if they are over 10% hi change them..Be glad to help
if I can , call on phone if you need to... Your old Raytheon friend
Harold W4PQW