Hello. Here joined is the schematic of a small deflection amplifier. Outputs H0 & H1 are connected to electrodes placed in a vacuum volume. These outputs are protected by varistors. High voltage to collectors is 200 V DC. Sometimes, not very often, the head Op-Amp (LM324) is burnt. The only credible cause is an ionization or ESD in the vacuum tube that 'come back' until LM324. I am surprised by the fact that only this Op-Amp is destroyed and absolutely never the HV transistors. What can I do more to protect this Op-Amp ?