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Old 18th July 2008, 01:42 AM   #1
d1983 is offline d1983  Canada
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Default Low voltage rectifiers?

This may be a bit of a strange question, but I was wondering if anyone knew of any tube rectifiers that operate at lower voltages. I'm working on a variable DC (~0-15V, around 15W) power supply for a friend that's really adamant about having tubes on there. I have no issues with going with solid state regulators, or really any other part of the circuit, I'd just like to have some tubes in the circuit. I was also thinking maybe using a valve voltage regulator if I can't come up with some rectifiers.
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Old 18th July 2008, 01:57 AM   #2
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Well, such things were done in the '30s when there was no other way... look up Tungar tubes, for example. But a 6V battery charger needed about 50V out of the transformer to work...

I do have a solid state Heathkit 0-60V power supply from the '60s that uses a VR tube as a voltage reference...
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Old 18th July 2008, 02:01 AM   #3
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Well 15 watts at 15 volts is an amp so you would need a serious mercury rectifier. You'll still get 10-15 volts drop across each tube so that must be taken into account. Don't forget the filaments will probably draw around 10 amps each.

I suppose you could use some 6C33s as rectifiers but suffer from a higher voltage drop. Those draw some hefty heater current as well.

Theres always tungar rectifiers but you may have problems finding a reliable supply of them.

The most sensible option is using a low voltage pentode as the error amplifier for solid state pass devices.
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Old 18th July 2008, 02:37 AM   #4
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Originally posted by astouffer

The most sensible option is using a low voltage pentode as the error amplifier for solid state pass devices.

Or a VR tube as a pilot light...

Actually, I had forgotten - there's a 1938 Thordarson booklet on my web page, which includes a 32V 3A power supply. It has 8 - '83 rectifiers, a 16 pound transformer and 11 pound choke and two 4 pound filament transformers (what do you expect from a transformer company...) http://www.audiophool.cjb.net/Misc/Thord_RSG_38.djvu
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Old 18th July 2008, 02:56 AM   #5
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Push-Pull tube amp with 15W output power, solid diode bridge, 400 Hz oscillator, opto-regulator. Easy!
Output transformer for such frequency may be very small.
Or a transformer from computer SMPS, but frequency must be much higher.
The Devil is not so terrible as his math model is!
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Old 18th July 2008, 02:46 PM   #6
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You could just use a silicon diode bridge and hook up a 5Y3's heater for looks. Cheating, I know, but your buddy's adamant about having tubes on this LV supply.

As stated before, your other choices are a hot, power-hungry mercury rectifier that's going to take days to heat up, or scarce tungar tubes that will be nigh-impossible to replace.
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Old 18th July 2008, 08:07 PM   #7
jlsem is offline jlsem  United States
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A full wave bridge using TV damper diodes will probably work just fine.

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