>Rich says:
>
>>I mean that the heater should probably not be DC grounded as long as the
>>possibility of a B+ to ground arc exists. . If such an arc occurs, the
>>internal insulation between cathode and heater can arc and possibly burn
>>out the heater. .
>
>
>Do I understand you as advising a bifilar filament choke, and tying one side
>of the heater and cathode together?
Yes
>That stops the heater cathode insulation
>getting punctured with a B+ to ground short; it suggests that the heater
>xfmr may need to float for any bias,
Correct
>(which won't be very much), and zener
>catching diodes (of greater voltage than the bias) can then handle any
>excursions during the B+ short.
>
>Of course, if you do not use a choke and then tie one side of the heater to
>ground, an arc that punctures the heater cathode insulation but leaves the
>heater intact still leaves you with a tube you can't use.
Jumper the cathode to the heater and it does not matter if the
heater/cathode insulation has gone to hell.
>You might even be
>able to get enough RF amps into the heater (from the input) to blow it for
>good.
>
The heater draws 10.5a.
>Don't sound an attractive approach to me................unless you're
>selling tubes.
>
Radios that will deliver over 10a of RF output are not common enough to
reap much profit. . .
>
cheers, Peter
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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