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Old 11th June 2005, 12:25 PM   #1
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Default 6,3VAC to 6,3VDC

I have a transformer with 6,3 sec. winding which was used for direct heateing in an older tube radio. What is the best way to get 6,3 VDC out of it. Tubes to be heated are two ECC88`s so I need cca 0,8A after regulatoin. Useing 2A/80V bridge and one 10000uF/25V cap over rails, I am geting cca 8,3VDC. Can I use let say 47K resistor to lower voltage? BTW. how if someone can say, 6DJ8, ECC88, 9622 react on direct AC heating?
Thanks!
Marijan
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Old 11th June 2005, 12:38 PM   #2
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Hey I have done the same question a few weeks ago.
See here
Maybe you will find your answer.
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Old 11th June 2005, 03:19 PM   #3
anatech is offline anatech  Canada
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What's wrong with 6.3 VAC AC at 60Hz? Just bias the heater supply about +30VDC above the average cathode potential. Best of all, there will be no HF electrical noise or extra heat to deal with. Cascode tubes excepted of course.
-Chris
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Old 11th June 2005, 03:55 PM   #4
jlsem is offline jlsem  United States
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Quote:
I have a transformer with 6,3 sec. winding which was used for direct heateing in an older tube radio. What is the best way to get 6,3 VDC out of it. Tubes to be heated are two ECC88`s so I need cca 0,8A after regulatoin. Useing 2A/80V bridge and one 10000uF/25V cap over rails, I am geting cca 8,3VDC. Can I use let say 47K resistor to lower voltage? BTW. how if someone can say, 6DJ8, ECC88, 9622 react on direct AC heating?
Just a 2.5ohm 5 watt resistor after the cap is the simplest solution. There is nothing wrong with burning off a couple of watts to get the correct heater voltage.

John
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Old 11th June 2005, 04:12 PM   #5
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There is another way to skin this "cat". Have the 6.3 VAC winding feed a "full wave" voltage doubler made from Schottky diodes. Use big 'lytics in the doubler stack. The doubler feeds a 7812 3 terminal regulator. The regulated 12 VDC feeds the 6922 heaters wired in series. The 6922 draws 300 mA. of heater current. You are good to go if the 6.3 VAC winding is rated at 1.2 A. or more RMS.
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Old 11th June 2005, 06:20 PM   #6
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I`ll test preamp tomorow with AC heating first and then decide what to do acording to your sugestions. Thanks for your answers.
Regards!
Marijan
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