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Old 25th October 2005, 02:09 PM   #1
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Question Using PSU Designer to calculate DC filament supply

I'm trying to use the PSUD2 to design a DC filament supply for 2 6SN7 tubes.
I assume you use a resistive load because its a heater, but where do I find the value of the resistance? I also assume that this resistance changes as the tube heats up.
I've never used DC for heaters, so I thought I'd give it a try.
Are the heaters still wired in parallel as AC heaters are?
Thanks in advance.
Glenn
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Old 25th October 2005, 02:50 PM   #2
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Default load resistance for PSU designer

Use a resistive load of 6.3 V / .6 A = 10.5 ohms. This is the hot value, valid after 15 or 20 seconds. Yes the initial value is lower, and your simulation for the first 15 seconds will be inaccurate, but so what ? I think you are really only interested in the steady state DC voltage and ripple.

As for series or parallel, that depends on wether you have 12.6 volts ( use series ) or 6.3 volts ( use parallel ) available.
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Old 25th October 2005, 05:27 PM   #3
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Thank you Robert
I have 6.3 volts, so I'll be using that.
Glenn
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Old 25th October 2005, 05:33 PM   #4
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Is the 0.6A is for 2 tubes in parallel?
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Old 25th October 2005, 05:49 PM   #5
Yvesm is offline Yvesm  France
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Try to set heathers in serie: less current, easier to filter, smaller caps, lower current peaks

a win win approach !

Yves.
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Old 25th October 2005, 06:05 PM   #6
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Using the series approach, if one tube heater fails the whole heater circuit fails, correct? I'm not sure this is a good or bad thing. I guess you can't use the circuit either way (series or parallel). The only hard part would be troubleshooting which tube failed.
Glenn
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Old 25th October 2005, 07:28 PM   #7
dhaen is offline dhaen  Europe
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You don't need to know the resistance if you use the constant current load option in PSUD2.

Series or individual is much safer than parallel, because of the potential voltage rise when one valve is removed.

Why do you need DC? It can be noisier than AC!
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Old 25th October 2005, 07:42 PM   #8
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How can DC be noiser than AC?
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Old 25th October 2005, 07:51 PM   #9
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Quote:
Originally posted by astouffer
How can DC be noiser than AC?
Diode noise. Hum is easily managed by twisted wiring and centre-tapped (or resistively divided) windings, referenced to ground. Indirectly heated filaments were created for this very purpose.
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Old 25th October 2005, 09:01 PM   #10
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Yes, I've never had a need for DC heaters in the past, but I like to have a "plan B" if needed. It's also another thing I'd like to experiment with just because I've never done it.
This is for a line level 2 tube 6SN7 preamp, so the wiring is pretty simple compared to other jobs I've done.

I never thought about the voltage rise if a tube is removed, good point. Of course I would never do such a thing

Here's my layout so far:

6SN7 preamp

Glenn
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