[time-nuts] Dead 5061B

[vilgotch1 at gmail.com]

I had a 5061A that had those symptoms. It had been running in Cs off mode
for a long time and the Ion Pump current looked like zero on casual
inspection but was actually barely perceptibly just off the zero mark. I
took that to mean that the ion pump had kept the vacuum in the tube very
well. The fault turned out to be no voltage at pin 4 of the 3500V supply A18
due to failure of the internal 100 Meg resistor. That resistor forms part of
a voltage divider from the +3500 that provides a "+3500 supply good" signal
to the rest of the system. 

If you can't find a replacement A18 you can repair it but it's a bit of a
job. You need to unsolder the base from the case and then the layout is
obvious. There's a soldered-over cap on the bottom of the unit that I assume
covers a hole used to fill it with nitrogen or some other inert gas. 

Good luck!

Morris



> Is there any hope. I would believe so. CS tubes are pretty tough. As Scott
> says HV supplies but you measured those and they appear good as you say.
So
> its a knock down drag out battle. You have nothing to loose so dig in.
> I wonder if the SRD may have popped. But its funny the ion pump is 0. That
> seems a bit odd. always a bit of crud in the tube that should make that
>kick up. My 10 cents.