Message text written by Alek Petkovic
>It could be the capacitor as suggested. It also could be the tube. I
only think I have heard one tube in 40 years talk back - but perhaps you
are
lucky enough to have that happen to you. If it is a tube, it will probably
not happen again for another 40 years.<
This is probably not relevant, but about twenty years ago I developed a
variable-voltage HV supply for the 4CX family which used a
ramp-and-pedestal phase-control thyristor stack on the input side of the
primary of the HV transformer. The rectifier stack had equalising resistors
and ceramic capacitors across each diode, and the racket made by the latter
as the phase angle was varied had to be heard to be believed! They only
became quiet when the SCRs were pretty well fully conducting. I assumed at
the time that this was due to piezo-electric effects in the dielectric,
although quite why they were so noisy with thyristor drive was never quite
clear.
I gather from other constructors of the supply that their rectifier stacks
weren't similarly vocal, so presumably it was something to do with my
particular batch of capacitors.
73 John
GW4FRX
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