Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: birt on March 11, 2012, 10:18:31 am

Title: 12V heater circuits
Post by: birt on March 11, 2012, 10:18:31 am

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?

Title: Re: 12V heater circuits
Post by: sluckey on March 11, 2012, 01:30:02 pm

I'd try the third drawing first.

Title: Re: 12V heater circuits
Post by: darryl on March 11, 2012, 06:57:44 pm

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.

Title: Re: 12V heater circuits
Post by: sluckey on March 11, 2012, 09:07:30 pm

Quote

The third drawing has a potentially serious shortcoming.

Ah, yes. I see what you mean.

Title: Re: 12V heater circuits
Post by: birt on March 12, 2012, 03:34:03 am

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.