Re: Top caps ;can you explain them?
Valves have top caps for various reasons:
* Not enough pins on the base to accommodate the connections (eg D1 diode with 3-pin base)
* Top cap grids to minimise capacitance to other electrodes (eg 6K7 RF pentode)
* Top cap grids to keep remote from heater pins to minimise hum pick-up (eg EF37A low noise pentode)
* Top cap grid for maximum insulation (just glass) for really low leakage - some electrometer valves
* Top cap anode for high-voltage operation (eg PL504 TV line output valve)
* Top cap cathode, again for high voltage operation (eg PY800 TV booster diode)
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