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Old 17th Feb 2009, 6:41 pm   #16
kalee20
Dekatron
 
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,061
Default 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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