On Aug 26, 2004, at 5:01 PM, Harold B. Mandel wrote:
Sirs,
The new amplifier will be running a pair of 3CPX1500A7 triodes
with floating filaments through bifilar chokes, powered by 5 volts
Direct Current through a floating bridge rectifier and filter.
In order to reduce the thermal shock to the filaments in the tubes
a method of reducing the inrush current is sought.
Harold -- According to Eimac, No inrush current protection is needed
with heater type cathodes. Thoriated-tungsten is the only type of
cathode that occasionally needs inrush-I protection. The reason is
that a directly-heated cathode has a much higher hot/cold R-ratio than
an indirectly heated one. In other words, a heater still has quite a
bit or R when it is cold, so the inrush current is not large. Eimac
says to limit inrush current on certain types of thoriated tungsten
cathodes, but says nothing about doing so on 3cx1500A7 and other heater
type tubes.
> ...
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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