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-   -   Tube pre-amplifier PSU (http://www.diyaudio.com/forums/tubes-valves/83781-tube-pre-amplifier-psu.html)

senderj 26th July 2006 10:15 AM

tub pre psu
 
2 Attachment(s)
I would like to use this psu for a tube pre with 2X 12AX7 and 2X 12AU7. the B+ is 275VDC and no B-. I need help on:

1. The 10H choke is too expensive for me. Can I replace it with R? What is the Ohm value?

2. For the 6.3V 3A from the transformer, is 3A enough for all (4 tubes) filaments? It should be 8X 6.3V filaments.

3. What is the purpose of the 50Ohm 5W pair in the 6.3V 3A?

EC8010 26th July 2006 10:41 AM

The 10H choke and 50 Ohm resistors are the least of your problems. The 317 will explode on switch-on. Search for "Maida regulator".

Each valve draws 0.3A heater current. 4 x 0.3A = 1.2A, so 3A is fine.

1/2W will be fine for those 50 Ohm resistors.

Frankly, the "design" appears to be a disaster conjured up by someone who doesn't know what they are doing. Given your level of experience, I'd advise you to leave it well alone.

Brian Beck 26th July 2006 12:18 PM

It's a bit scary because the drawing style of the schematic makes it look like it was copied from a manual. You have to wonder if anyone built it.

sorenj07 26th July 2006 05:35 PM

what's wrong with it?

Tweeker 26th July 2006 07:09 PM

The LM 317 doesnt want to see more than 35 Volts, your missing some protection circuitry.

Sheldon 26th July 2006 08:43 PM

More specifically, the 317 can't take more than 35 volts from the input to the output or to the ground connection. I suppose it's possible for a circuit like this to function, if the timing of the input voltage rise is such that the caps on the output and ground pin could charge up before the 35V difference is exceeded. This issue is the same in reverse too. So if the input cap discharges while the output cap is still charged - poof, out goes the magic smoke. Don't count on it to be reliable, and don't hook up anything to it that can't stand the full voltage output with the regulator shorted. Or, use a better design. As EC8010 suggested, look up Maida regulator. http://www.national.com/an/LB/LB-47.pdf
Sheldon

senderj 28th July 2006 01:48 AM

Thanks for all the replies. I'm glad that I ask before action.

But the Maida regulator, from the link, only output up to 160V. I need 275V. How can I mod it to this voltage?

SY 28th July 2006 02:25 AM

I'd read the app note thoroughly before embarking on a design. All the design equations are in there.

jarthel 28th July 2006 02:06 PM

Quote:

Originally posted by SY
I'd read the app note thoroughly before embarking on a design. All the design equations are in there.

I was reading the PDF Sheldon linked and I can't see any app notes. can you tell me where it is? thank you.

SY 28th July 2006 02:13 PM

http://www.national.com/pf/LM/LM317.html

This page gives you links to all of National Semi's datasheets and app notes for the 317.


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