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Old 5th February 2012, 04:10 AM   #1
jono1 is offline jono1  United States
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Default Damper rectifier tubes & voltage doubler

I'm thinking of using two damper rectifier tubes in a voltage doubling configuration.

Any problem with that topology?

Thoughts?

Thanks in advance.
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Old 5th February 2012, 04:28 AM   #2
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The only issue I can think of off the top of my head would be the heater-cathode voltage rating,but I think it's pretty high on most dampers?
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Old 5th February 2012, 04:40 AM   #3
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Two diodes implies a half wave doubler. Current will be somewhat limited and in order to prevent HK breakdown you will have to elevate the second diode's filament DC potential higher then the first one. This will involve a seperate filament winding or transformer. You may also be limited in capacitor size with tube rectifiers. SS is much more pragmatic.
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Old 5th February 2012, 06:33 AM   #4
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This is a full wave voltage doubler:

Click the image to open in full size.

using tube dampers, i think you need 2 separate 6.3 volt windings insulated for high voltage.....this is doable....
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Old 5th February 2012, 08:27 AM   #5
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Hi!

TV dampers work nicely. I have used them this way already. As others pointed out, watch the HK voltage. Most TV dampers have a 900V rating for heater negative against Kathode. Theoretically you can use a single heater winding for a doubler which delivers up to that voltage and have the winding connected to ground. I'd stay clear of that limit and say up to a supply delivering 600V use a single winding. Above that, two separate windings. Connect the heater of the two diodes at one side to the respective cathode in that case.

Also don't use too much capacitance after the rectifiers. 5-10uF. You will need at least a LC filter following that to get ripple down

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Old 5th February 2012, 02:56 PM   #6
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Default Dampers

Whats key with damper tubes is the steady state peak plate current and the dc output current. The peak current is usually over 1 amp and the dc is 200 to 400ma. Used as rectifiers you need to watch the peak current on power up. You can see this in LTSpice. As you increase capacitance the peak current will exced the peak current rating. To tame this insert a 100 to 150 ohm resistor into the secondary leads.
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Old 5th February 2012, 06:38 PM   #7
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Hi!

Or use them with choke input filter


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Old 5th February 2012, 10:06 PM   #8
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The Greinacher, AKA "full wave", doubler is (in fact) a pair of 1/2 wave rectifiers wired back to back. To get decent regulation of the resulting rail, large caps. in the doubler stack are in order. Another poster's remarks about SS diodes being the practical solution is spot on. However, I think it may be possible to safely use damper diodes in combination with good sized caps. in the stack. Install a CL-90 inrush current limiter, whose cold resistance is 120 Ω, in the line between the center of the cap. stack and the power trafo. Perhaps as much as 150 μF. per cap. will be fine. 68 μF. parts should be "a walk in the park".

Negative temperature coefficient (NTC) thermistors are common enough in SS rectified PSUs. It seems they may be exploited in combination with vacuum diodes too.
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Old 6th February 2012, 05:59 PM   #9
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I had good results using four damper diodes in a multiplier fed from an isolation transformer (splitting a 220 V primary that passed a hipot test for separate use of the coils). The amp used 33GY7s or 33GT7s (minor connection difference). The Op-amp driver supply used AC from a tap off the bottom filament in the string clamped with a MOV in case the tube was pulled. Screen-current-canceled cathode-sampled feedback made distortion very low even with low bias currents. Although the ability to drive grid current wasn't needed, the direct coupled feedback driver eliminated blocking distortion and the need for any adjustment or matching when changing tubes. The damper diodes and small sweep tubes share a high peak to average capability, which was a perfect fit for low bias current and music use. A reduced voltage fan was included but I didn't feel any need for it except with square wave test signals (but I keep tubes cooler than most). I admit I probably would have never used damper diodes if those tubes didn't have them included, but I really liked the result and enjoyed seeing a level of performance I once thought was impossible with junk-box tubes.

Last edited by riccoryder; 6th February 2012 at 06:09 PM. Reason: mistakes that defy all reason
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Old 7th February 2012, 01:28 AM   #10
jono1 is offline jono1  United States
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Thank you for the helpful info!
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