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previous: Dan McCue I dont know why it would. Functiona... -- 2/9/2004 8:46 PM	View Thread

Re: DC heathers on power amp? why not?

2/9/2004 10:49 PM
Dave B	Re: DC heathers on power amp? why not? you can use a dc stand-off supply and put dc on all the heaters. Typically you use a series resistance from B+ to ground, lets say: B+ -470k-100k-ground. At the junction of the resistors filter with a 10uf cap. Your goal is something close to 75vdc at the junction of the resistors & cap. Now connect the center tap of the 6.3V circuit (or an artificial center tap of 2 100R resistors) to the 75vdc node you've created and viola! The benefits of dc heaters but without the extra current draw. The reason the power amp of a push/pull amp doesn't need or benefit from dc (besides the other reasons mentioned)is because the power amp is a humbucking circuit and any ac hum is canceled out. A single-ended power amp on the other hand, can benefit from dc since it's not humbucking and can have problems with ac hum. db

2/9/2004 10:49 PM

Dave B

Re: DC heathers on power amp? why not?

you can use a dc stand-off supply and put dc on all the heaters. Typically you use a series resistance from B+ to ground, lets say:
B+ -470k-100k-ground. At the junction of the resistors filter with a 10uf cap. Your goal is something close to 75vdc at the junction of the resistors & cap.

Now connect the center tap of the 6.3V circuit (or an artificial center tap of 2 100R resistors) to the 75vdc node you've created and viola! The benefits of dc heaters but without the extra current draw.

The reason the power amp of a push/pull amp doesn't need or benefit from dc (besides the other reasons mentioned)is because the power amp is a humbucking circuit and any ac hum is canceled out.

A single-ended power amp on the other hand, can benefit from dc since it's not humbucking and can have problems with ac hum.

db

Replies:

Dan McCue Hi Dave, I think you lost me a litt... -- 2/10/2004 2:26 AM