Re: What happens if a valve's cathode becomes electrically detached ?
I suppose that to begin with a disconnected screen grid would be raised to a somewhat positive potential by its capacitative coupling to the anode, but as soon as any electron flow from the cathode began there would be a tendency for the screen grid to intercept some of those electrons and, therefore, head downwards in potential, so throttling the electron flow.
As I say, the soldering on the pins looked fine under a magnifying glass, but since the valve is back with the retailer now I'm not in a position to re-check or to try doing anything about it.
The grid current did start and stop pretty quickly. In the light of kalee20's comments that could be explained by the HT, once it was established, sweeping the electrons through the control grid. The HT supply is solid-state rectified, but with a rather large smoothing capacitor, which doesn't charge instantaneously.
Cheers,
GJ
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