[Central-Electronics] 600L questions

[Tom Hankins]

Anybody out there with good understanding of the 600L circuits-mainly the
12at7 in the mismatch control circuit? I have a problem with burning up the
cathode resistor and it shorts the tube also. It must be drawing a huge
amount of current because the resistor goes up rather violently. It has
happened 2 times and after the 1st I replaced the socket and all surrounding
wiring along with the 12at7 tube. Worked fine on the bench for a few days
and passed all power out tests and a final check after putting it back in
the cabinet caused to light up again with a lot of smoke. The relay coil
shows a proper 10K and I wonder if anyone has seen one with an intermittent
short? 

Any help or suggestion on who I could discuss it with would be welcome.
Thanks!

Tom Hankins

K0EOA