Re: The "Sussex" Homebrew Valve Tester.
Hi Mike just read through your problem, it seems to me that with a HT of 410V the MPSA92 has to drop 110V and at approx. 4ma to supply the zeners this makes for a little over 400mW dissipation. It is riding close to its limits so either you need to reduce the HT feeding or substitute another transistor with higher dissipation spec such as MJE350.
Dave
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