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Old 21st April 2008, 12:36 PM   #21
nitrate is offline nitrate  United Kingdom
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Yup, Voltage doubler is the way to go as i will already have +_40v for the fet output stage. I should be able to get 140 to 150V out of it. I'm hopeing this will be more than enough for the valve gain stages. I have an example of this used in an RF amplifier i use and i've never had any trouble with it to date. Still cant understand why my triode CCS doesnt work tho....

Anyone any ideas??

Leigh

P.S the 'Tube sound' is exactly what i dont want. My aim is for absolute transparancy. I'm hoping the tubes can supply this as they seem rarther linear on paper.

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Old 21st April 2008, 04:37 PM   #22
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Frightened of high B+ ? Reminds me of the ECH83 found in car radios of the 1950's. Really low space charge working. There are still around in surplus stores.
One can bodge the multi-electrode in all sorts of configurations.

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Old 21st April 2008, 06:41 PM   #23
wa2ise is offline wa2ise  United States
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Quote:
Originally posted by nitrate
Yup, Voltage doubler is the way to go as i will already have +_40v for the fet output stage. I should be able to get 140 to 150V out of it.

I did this scheme with a 2nd bridge to get some higher voltage at low current, in a CD player I was modifying for tubes:



Click the image to open in full size.

The bottom bridge was an existing one in a CD player power supply. As you have +40 and -40 from a bridge supply (I'm guessing that you used a bridge), you could have +120V and if you return the tube circuit current to the -40V, it would be like 160V.
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Old 22nd April 2008, 08:39 AM   #24
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I have never seen a "stacked bridge" before. I can sort of see how it works, and I guess, like a doubler, current decreases as voltage goes up?
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Old 22nd April 2008, 08:47 AM   #25
nitrate is offline nitrate  United Kingdom
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Good idea WA2ise, i have not considered tieing the two bridges together for a sneaky 80V advantage. As things are set up now that would give me about 240V ( +-40 + 80*2 ). Lol, maybe a bit much as i want to keep B+ to a minimum. Handy concept tho... Just don't like those caps linking the bridge.

Leigh
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Old 22nd April 2008, 08:59 AM   #26
nitrate is offline nitrate  United Kingdom
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Looking closely at the stacked bridge it actually looks like it will short out to me???


Leigh
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Old 22nd April 2008, 09:53 AM   #27
nitrate is offline nitrate  United Kingdom
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anougher look and it dosen't short LOL. An ickley little circuit

Leigh
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Old 22nd April 2008, 11:47 PM   #28
wa2ise is offline wa2ise  United States
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Quote:
Originally posted by hotbottle
I have never seen a "stacked bridge" before. I can sort of see how it works, and I guess, like a doubler, current decreases as voltage goes up?
That's essentially it. I did this to create some B+ to supply a few ma of current, in a CD player that I was adding a tube output buffer CF circuit into. Didn't feel like using a 2nd power transformer.


Click the image to open in full size.

http://pw2.netcom.com/~wa2ise/radios/tubedac.htm
for more CD players with added tubes.
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Old 23rd April 2008, 11:03 AM   #29
nitrate is offline nitrate  United Kingdom
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Nice job WA2ise. Call me thick but on my 6922's there is a screen pin ( pin 9 ). Am i to belivethis is an internal sheild to help stop cross talk between the two triode sections? if this is the case is it wise/safe to connect this screen to ground??

Also has anyone had any problems with connecting two or more valve heaters in series? is this wise?

anybody got a good example of a valve CCS? as i still have problms with mine. It seems the valves are very sensitive to changes in anode voltage.

Leigh
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Old 23rd April 2008, 03:00 PM   #30
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Personally, I wouldn't try a valve CCS if you are trying to minimize voltage on a power supply. A transistor cascode will work much better and at a much lower voltage.
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