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Old 26th September 2004, 02:43 AM   #1
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Default Designing a simple dc filament supply?

I have heard the reports of benifits from using dc on your filaments and would like to experiment with such. I wish to build a seperate filament supply to send some dc to my heaters. As being an "electrician" by trade, I have access to sealed storage batteries that could be used to supply pure dc. However, this would entail alot of charging in between "gigs". I need some help if anyone has a schematic of something simple in the way of a dc filament supply and I dont need anything real fancy. Just pure dc thats all. Any suggestions or a scematic would be excellent! Thanks everyone. The DOC
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Old 26th September 2004, 09:48 AM   #2
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It all depends ... (don't you just hate answers like this?) ... on how much current you're thinking of. If it's the early voltage amplification stages only, which is where DC heating is likely to do the most good, then (assuming 6.3v heaters) you probably need around 1 amp max.

A low voltage drop SS bridge rectifier from a 6.3v secondary winding, followed by a big capacitor (say 10,000 uF), could be all you need. You can try modelling this with PSUD2. If you find you're getting a bit too much voltage, try putting a forward-biased diode or two in series with the output.
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Old 26th September 2004, 10:36 AM   #3
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This is the one I use - it works great

It could be further simplified as an LM317 with a 2N3055 pass transistor. But when I needed a filament supply, I had a box of discrete's and no 317
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Old 26th September 2004, 09:11 PM   #4
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Default Dc Filament supply

I have on hand a 6.0-0-6.0 center tapped transformer rated at 3a, and would like to be able to use it as part of my filament supply, at least for my driver stages. Could I use this in my filament circuit? Hey geek, thanks for the input as well.! What are the specs on the transformer you are using in that circuit? I would like to e-mail you about this design so drop me a line at if you have time. If I can use this transformer I have, what kind of rect and filter should I use? What about using a choke in the filter section? I know I have alot of questions, but you guys really make life a little easier sometimes. Thanks to all.
The Doc.
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Old 27th September 2004, 02:25 AM   #5
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'k Doc, I'll shoot you an email

The tranny I use on this project is a 12-0-12 @ 3A liberated from a CB radio desk power supply. It can handle inputs up to 36VDC with forced-air cooling on the heatsink.
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Old 27th September 2004, 10:31 AM   #6
SHiFTY is offline SHiFTY  New Zealand
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On my 6B4 SET, DC filaments are necessary to cure the hum.

I just used a toroidal transformer with dual 9V 1.1A windings.

Each winding then is connected to a schottky bridge into a 5600uF cap, then a dropping resistor (3 ohm 5Watt) This gives me 6.1V which is close enough

Works fine, but make sure the caps are rated for the ripple current
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