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Diode for DC heater
Diode for DC heater
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Old 30th December 2006, 11:56 PM   #1
dsavitsk is offline dsavitsk  United States
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Default Diode for DC heater

I am looking for diodes to convert an AC heater to a DC one. The current draw is ~2A and the winding is 6.3VAC, so something with minimal voltage drop would be good. Suggestions? With an old trabsformer, I just grounded the center tap and all was well, but I got a new transformer, and this is not working.

Also, if anyone has a favorite circuit for doing this that would be appreciated. I figured I'd use CRC with a couple of 10KuF caps unless someone has a better idea.
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Old 31st December 2006, 12:06 AM   #2
Sheldon is offline Sheldon  United States
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I've used 1N5821 with good results. Also 6.3V and about 1.8 amps.

Sheldon
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Old 31st December 2006, 01:07 AM   #3
anatech is offline anatech  Canada
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Diode for DC heater
Hi dsavitsk,
Hum problems? Bias your heater line up to 30 ~ 50 VDC above ground. Bypass the heaters to ground when doing this.

This eliminates any high frequency pickup from tring to rectify and filter your heater. The transformer should run cooler than rectifying the heater line also.

-Chris
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Old 31st December 2006, 04:08 AM   #4
Wavebourn is offline Wavebourn  United States
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Diode for DC heater
I have lot of 1N5822 barrier Shottky diodes for such purposes.

Click the image to open in full size.

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Old 1st January 2007, 03:10 PM   #5
Sheldon is offline Sheldon  United States
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I'd like to try this one for a SS amp project (idle current around 1 amp) and wouldn't have a HT supply. Got a version of that which could run with just the low voltage transformer? Maybe a doubler for the bias supply? Or does the required impedance at R1 have to be too high to allow a lower voltage?

Sheldon
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Old 1st January 2007, 03:29 PM   #6
poobah is offline poobah  United States
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Use PSUDII and run a sim on your proposed DC heater circuit... pay close attention to the resistance of the supply winding. You will find that it is very difficult to get 6.3VDC from an 6.3VAC winding... you need a HUGE cap.

Also, you are trading an innocent sine wave in your heaters for a spectral nightmare... high frequency stuff... from Schottkys especially. The capacitance from filament to cathode begins to look like an open door at these frequencies.

Don't get me wrong... I'm all for DC heaters. I just think you need to start with at least an 8-9 VAC winding first. Using 6.3 VAC is on the hairy edge of praticality at best.



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Old 1st January 2007, 04:19 PM   #7
anatech is offline anatech  Canada
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Diode for DC heater
Hi Poobah,
I'm very glad to see you around. Happy New Year dude!

This is what I've been trying to say all along. I'll add that I used to like DC heaters, but I've seen the light an I now think AC is the best way to go with the possilbe exception of low level stages.

-Chris
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Old 1st January 2007, 04:37 PM   #8
poobah is offline poobah  United States
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Hey Chris!

Taking the day off... feel like stirring the pot a bit here!

And happy New Year to you as well... and everyone else for that matter!

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Old 1st January 2007, 08:41 PM   #9
Wavebourn is offline Wavebourn  United States
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Diode for DC heater
Poobah, you are right from theoretical point of view about spectral differences, but my amps are deadly quiet.

Sheldon, R1 to B+ is a simple kind of a current source, you may use CCS from doubled low voltage: you need more than output voltage + 6V + ripples + drop needed for CCS to work well. In most cases you will get it.
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Old 2nd January 2007, 12:16 AM   #10
poobah is offline poobah  United States
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Wave,

RIGHT, in the case of full blown regulater, as you've shown. I am just thinking strictly along the lines of plain bridge/RC PSU.

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