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OD3/OA3 voltage regulation design
OD3/OA3 voltage regulation design
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Old 21st February 2008, 05:17 AM   #1
Carlp is offline Carlp  United States
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Join Date: May 2006
Location: A New England
OD3/OA3 voltage regulation design
Default OD3/OA3 voltage regulation design

OK, I'm new to working out designs and tweaks to designs, so please be patient. I'm considering series use of OD3 and OA3 to provide 225V B+ for a 12B4 and/or 5687 linestage. I'm wondering if I can get away with a single stack of these (one of each) and still provide the 11mA (5687) or 29mA (12B4) PER channel current requirement for the triodes.

I know in theory I could simply calculate the ballast resistor for the regulators factoring in the full current requirement for the circuit, plus the current requirement for the VR tubes (15-20mA, depending on what works). I'm guessing I'll need different ballasts for the two circuits given their different bias currents, but assuming the trafo and rectifier/inductor PSU can handle the power requirements, can I use one OD3 and one OA3 in series and still provide two channels without a problem?

Is this a reasonable proposition? Am I missing something? Will the current variation of the two sides of the 12B4 or 5687 swing enough that I need to figure that into my calculations? And am I correct that if I simply account for 58mA for both sides of the 12B4 and 22mA for the 5687, and select the ballast resistors carefully I should be safe?

Thanks a ton,
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Old 21st February 2008, 05:57 AM   #2
pchw is offline pchw  United States
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Join Date: Apr 2006
Location: Fremont, California
OD3/OA3 voltage regulation design
Take a look at the 2 articles that Zen Mod posted in
My gut feeling is that one stack is not good enough for 80ma. Assume how much variation of the voltage you want to regulate and start from there to determine the value of the resistor to use. The typical starting is to have the VR to shunt the same current as the main circuit which apply 3 stacks in your case!!
- Fred -
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