[Milsurplus] TCS 9

[W7QHO at aol.com]

Mike,

Your 490 volts on the PA is a bit hot for the TCS (Navy ran them at 400) but 
I don't think this is the problem unless the voltage is going MUCH higher on 
key-up.   Easy to check.

I remember having a problem like this when I first fired up my TCS.   There 
is an arc suppression circuit connected to the high voltage line running from 
K102 out to the modulator and PA.   This consists of C128B (erroneously 
identified as C120 in my last message)   connected to ground through a 470 ohm 
resistor (R120).    In my rig, C128B was open (no capacity) and I saw the same kind 
of arc you are experiencing.   Check C128B (0.1 mfd, dual bathtub) and if OK, 
try adding an additional 0.1 mfd of capacity or so in parallel with it.   
Leave R120 in the circuit as it limits the charging current into the capacitor 
when the relay contacts close.

C128 and R120 are located underneath the roller inductor and can be reached 
from the underside of the chassis.

I previously misidentified C128B as C120B as mentioned before.   C128A, the 
other half of the bathtub, and R120 perform the same kind of arc suppression 
function on a set of contacts in K103 that switch the receiver screen voltage on 
and off, the muting scheme used by the TCS system.

Good luck.

Dennis D. W7QHO
Glendale, CA