Dose instability

Error: Very instable dose rate or no dose-rate at all.

Frequency servo is extremely instable. Much more than when hunting. Amplitude of the phase legs varies by a factor of two within a second.

We had X6 running perfectly and X18 not running at all.

It is likely that timing of thyratron firing is effected.
Check the thyratron grid connection for a burned contact. Usually this does the trick, if not, replace thyratron.