>
>I've noticed something strange in amp articles
>featuring indirectly heater cathode tubes like the
>3CX800A7 or 8877. Some have a bi-filar choke in the
>filament line, while others feed the filament directly
>from the filament transformer. A variation of the
>latter is grounding one side to provide a return
>through the chassis, and bypassing the live side to
>ground with a .01 uF disk (Ten-Tec does this on the
>Titan).`What's the best approach?
>
? I have seen several kaput 8877s that arced between the cathode and
heater during some kind of glitch. // In my opinion the safest approach
is to not stress the (unrobust) cathode/heater insulation. . In other
words, put a jumper between the cathode and the heater, and use a heater
choke - the same as one would do for >>30MHz operation. / Also: Do not
ground - or bypass to ground - either side of the heater. / Use glitch
diodes in the negative hv return . / Use a glitch diode in the hv
positive lead. On the other hand, if you have a free supply of tubes,
the safe approach really doesn't matter.
cheers, Kevin
- Rich..., 805.386.3734, www.vcnet.com/measures.
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