[TenTec] Century 21 audio hum

[w8au at sssnet.com]

At 03:35 PM 5/30/2017, Josh Gibbs wrote:
>The hum totally
>disappears when running on external 12VDC, but the transmitter can not be
>operated due to lack of 23V unregulated power required for the T/R switch.

Josh:   I'm not sure about this T/R switch question.  Years ago I used to run
my C-21 mobile by backfeeding the 12V Aux socket from the auto's 13.8 
V battery.
(through fusing, of course)

Worked fine.  The only problem was that the amp collector current
meter in the PS was bypassed and did not indicate anything.

I must confess, however, upon first hooking up the rig in the vehicle I cranked
up the drive to where I thought it should be and had a few contacts.  When
I decided to put the Bird meter on it to see what the actual output I 
was shocked
to see 70 watts!  :-[  Whoops!   However no damage to the C-21....  a truly
rugged rig!

Needless to say, this did not happen again... I marked the drive pot 
at 35 watts
output for the extent of it's mobile operation.  Eventually installed 
a TT Scout
in it's place... (with the magnetic breaker in the A+ lead)

Still have the trusty C-21 in the shack.

Perry   w8au