Lifting AC heaters on DC w/ center tap?

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glpg80
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Lifting AC heaters on DC w/ center tap?

Post by glpg80 » Sun May 03, 2020 4:37 pm

If you lift the AC heaters on DC using the center tap, does the DC source need to be completely floating or can the other side be referenced to ground?

danman
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Re: Lifting AC heaters on DC w/ center tap?

Post by danman » Sun May 03, 2020 6:41 pm

Are you simply wanting to elevate the heater winding by connecting the filament CT to the power tube's cathode or attaching it to a voltage divider in the b+ rail? Or...are you rectifying your filament winding to run the preamp heaters on DC voltage?

glpg80
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Re: Lifting AC heaters on DC w/ center tap?

Post by glpg80 » Sun May 03, 2020 7:29 pm

Non of the above, I have a standalone PS with isolated outputs and have to ground one side to get 12V+. The game plan was to elevate the power tubes 12V DC + 6.3VAC.

It’s isolated and can do -12V as well if needed by grounding the opposite side which means at least one side must be grounded which has me on edge.

I’m using a standalone because I’m using it for multiple purposes. DC pre Heaters, elevate the power tubes standard AC, and to power some 12V relays. The supply can be cranked up to 12.9V to account for voltage drop under load.

glpg80
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Re: Lifting AC heaters on DC w/ center tap?

Post by glpg80 » Wed May 06, 2020 11:47 am

I'm going ahead with the heater lifting method I've mentioned. I've thought about it and my reasoning is that this supply is floating and doesn't have a dedicated chassis ground which could short the rectification of that design should it exist. Instead this supply is a switching supply hence the floating output. To get the 12V output, I need a ground reference on the output which is implied - hence there shouldn't exist a short through a rectification stage to take out any diodes because such a path does not exist.

I have a variac and will monitor the current draw through the 12V supply to the center tap. Since very little current is drawn from the center tap of the heaters to supply AC heater current, it should be very easy to tell whether it is working as intended.

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