what can cause the EHT to be excessive high? My monitor is shutting down (x ray protection). i have about 20% higher EHT that usual. after moment, the monitor shuts down.

The EHT transformer has a capacitor inside this if part of the EHT voltage stability loop can cause the EHT to overshoot on start up.

It was quite common on some chassis the capacitor goes low in value and the effect you are seeing happens.

It also could be caused by short EHT B+ fet if the rail supplied from is a high voltage and not a boost type fed from a low voltage.

Rich

The FET is booster.
The input voltage is lower than the output voltage.
I thought, that the FET-gate drive has excessive pulse-width.

You say that the EHT-filtering capacitor is low... so what will happen,
if i connect my own 60kV 2,5nF capacitor between EHT and ground ? Is it good or bad idea ?

Thanks