Quote:
Originally Posted by beery
I never heard of one having 2" neck stems to re-mount ES guns...
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Andy,
Yes, even if a tube re-builder was to be re-born in our modern world, it is highly unlikely an ES tube would get re-built. This is why I was contemplating other solutions.
On your initial 3kV problem, I came up with a very simple way of delaying the EHT in electrostatic sets until the heaters had warmed up. In the Andrea KTE-5 for example, the EHT is derived from a separate transformer & 2X2, it came up much faster than the scan stages, as did the CRT heater. So the beam could burn the crt phosphor in that interval before the HT and scan got established.
One day I notice that a typical audio output tube, like a 6v6 (and many others) have about a 270R to 330R cathode resistor and it drops roughly around 12V for the bias. Suddenly the penny dropped and I realized the cathode resistor could simply be replaced with a 12V, 270R to 300R relay coil from a common garden 12V relay.
So if the relay coil is used or incorporated into the audio output tube's cathode, the audio stage functions normally...but, it takes time for the tube to warm up and get enough current to close the relay and the HT has to be established to do that and by then all other stages are running. A perfect delay, the relay contacts were simply put in series with the mains supply to the EHT transformer primary, to delay the EHT. So its a quick & easy way to create a delay after turning a set on, if you need to, so as to benefit some part of a circuit in the set.