12V heater circuits

[birt]

i have a 12V heater connection on the PT. the original amp had the 2 preamp tubes in series and the 2 power tubes in series. no CT.

i have to redo the wiring so i was thinking if i could improve it.

the first drawing is as it was originally.

would this setup benefit from an artificial CT as in the second drawing?
or can i just use the heaters to create an artificial CT as in the third drawing?
or should i still add the resistors to this setup to prevent it from going terribly off balance if one of the heaters goes bad?

[sluckey]

I'd try the third drawing first.

[darryl]

The third drawing has a potentially serious shortcoming. If any one valve is unplugged, or somehow goes open circuit, then the voltage across two of the heaters will drop, while the voltage across the third heater will rise.

I have used the second drawing arrangement without problems.

[sluckey]

The third drawing has a potentially serious shortcoming.

Ah, yes. I see what you mean.

[birt]

that's what i meant with "going terribly off balance if one fails"

and now that i think about it again, adding the resistors to the third drawing would help yo prevent this but will this have any advantage over the second drawing? that one will stay balanced anyway. i'll go for that one.