Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => EZ Board postings => Topic started by: Geezer on June 18, 2005, 06:01:50 am
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Hoffman Amplifiers
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> DC Heaters
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Michaiel Roberts
Junior tube assistant
Posts: 1
(4/1/04 12:59 pm)
DC Heaters
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Can anyone explain how to convert from AC to DC heaters to minimize hum?
ganzonimx
Hey get your own solder
Posts: 450
(4/1/04 1:42 pm)
Re: DC Heaters
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Have you tried to "float" the heaters on a positive level? that reduces hum in a nice and simple way.
If you have a cathode-biased amp, just connect the junction of the two 100 ohm restores that go off the heaters to the cathode resistor (tube side).
If its a fixed biased amp you have to build a voltage divider, Look here for a idea how to do it.
Cris
Michaiel Roberts
Junior tube assistant
Posts: 5
(4/1/04 2:43 pm)
Re: DC Heaters
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Cris
this link is to the compressor i am working on. www.waltzingbear.com/Sche..._Level.htm I am not sure i understand what you are describing, but maybe this schematic helps understand which bias circuit i have.
thanks
michaiel
EDIT: I fixed the link.
Ken
Edited by: GroundhogKen at: 4/1/04 2:53 pm
Tiny Daddy
I will work on all amps
Posts: 583
(4/1/04 4:12 pm)
Re: DC Heaters
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One way is to get rid of the tube rectifier then series the 5V and 6.3V filament windings, use a bridge rectifier and large cap, and then a 3-terminal regulator.
ganzonimx
Hey get your own solder
Posts: 454
(4/1/04 5:14 pm)
Re: DC Heaters
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What hum do you have? is it 50/60Hz or 100/120Hz?
What did you already to reduce hum? did you replace all the electrolytic filter caps?
Cris
Michaiel Roberts
Junior tube assistant
Posts: 6
(4/1/04 5:47 pm)
Re: DC Heaters
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I havent bult this unit yet. I have been looking into building this and wanted to understand the possibilities of anything to insure a good assembly. here is the link to the schematic if you want to look...
www.waltzingbear.com/Sche..._Level.htm
thanks
michaiel
ganzonimx
Hey get your own solder
Posts: 455
(4/1/04 6:29 pm)
Re: DC Heaters
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Look at Doug's Library of Information, there is a page about heater circuits.
The schematic has a odd tube in the first stage, but it seams not to be a high gain stage, so with a proper heater circuit design hum will probably not be of big concern.
Cris
Tiny Daddy
I will work on all amps
Posts: 585
(4/1/04 7:28 pm)
Re: DC Heaters
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If you are going to all the trouble of building a compressor I suggest the Teletronics LA-2A and use a 250V solid-state regulated supply, available cheap. Maybe buy a 5V regulated supply too, with an adjustment that, turned up all the way, will get close to 6V for the filaments. Quiet as a mouse.
Michaiel Roberts
Junior tube assistant
Posts: 7
(4/2/04 10:05 am)
Re: DC Heaters
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Thanks guys!
michaiel
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