John -
Normally, the TR-7 switches both the AC supply to the PS-7 Power Supply
- AND - the +12VDC to all of the transceiver with the exception of the
PA stage. This was done to allow the transceiver to be used on either
AC or DC if mobile use was desired.
So if the external 12 VDC supply is ON, turning the transceiver on or
off with the PWR OFF switch will turn off all but the PA.
The AC part of the PWR OFF switch is connected to Pins 1&3 and Pin 2&4
of the PS7 Control connector (J5) on the TR-7.
There was a mod circulating to remove the AC from the transceiver
cabinet by putting a relay inside the PS-7 and using the relay to
control the PS-7 AC primary.
These switches do fail, and are essentially irreplaceable, due to being
mounted on a dual control. I leave my PWR switches ON, and use an
external power switch. I do this for all my older equipment that has
control mounted power switches just because they are so difficult to
source if they do fail.
I wouldn't just plug in the PS-7 without doing some checking. You can
check the continuity between Pins 1&3 and Pins 2&4 to see if the PWR OFF
switch is still functional. If it is, then you are probably ok.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
John Stringer wrote:
I have been using my TR7A with a non Drake Power Supply. When I do this the
front panel on off switch switches the 12v. I always thought this strange as
it is supposed to switch the main supply to the PS7. Two questions:
1. Is it normal that it switches 12v?
2. Is it switching the full 23amps or just the receiver part if it is a
Drake arrangement rather than a modification?
Now I want to use a PS7 instead of the non Drake supply and this leads to
question3!
3. Is it safe to plug in the PS7 and will the front panel switch turn on the
mains voltage?
John GI3KDR
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