[time-nuts] Dead 5061B

[AC0XU (Jim)]

Time Nuts-

This 5061B was working fine until a recent power failure, after which the unit would not come on line (alarm light stayed lit).

Major symptoms now: 

Beam I  ; Second Harmonic;  Ion Pump Supply are all 0 on front panel.  All other front panel readings are normal. (except for battery, which th unit doe snot have).

L4P2 signal is 16.832 MHz 1.7 V p-p  (perfect - suggesting that A1 synthesizer is fine)

Going through 5-173 A12 Cesium Beam Tube Operational Checks:

5-175 Low Frequency Coil Check. Everything is fine except that tweaking the external oscillator frequence/amplitude has no effect. Beam I is always 0.

The text says "If the beam current is not restored, it indicates a problem in the the cesium beam tube power supplies (A11, A15, A18, or A19) or in the cesium beam tube itself.

A11 = Cesium Oven Controller - front panel reading is fine. Removed A11 from the chassis and made the tests in  5-141.
 Everything fine. +- 16V and -10V all fine; Cs oven voltage fine; the thermistor tests out at 435 ohm vs. the 430 ohm on the label.

A15 = Power Regulator Board - main +18.65V is fine

A18 = +3.5KV supply - measured and is fine

A19 = -2.5KV supply - measured and is fine

I am inclined to conclude that the tube is dead. I don't understand why that occurred suddenly in conjunction with a line power failure.

Can I have any hope that the tube is still o.k.?  Any ideas?

Thanks!

Jim