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Old 24th April 2011, 01:39 PM   #1
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Default Help running RH807 at higher voltage

So I've decided to try out the RH807 as my second build, after the success of the RH84. It's almost the same circuit but with differently-rated components, and the choice of 807s, KT66, or 6V6 as output tube. Suggested voltage is 320-0-320 to produce a B+ of 350V. The author suggests it can be run with higher voltages, but with appropriate modifications... which he doesn't specify.

I'd like to run this with a 6L6 at around 400V, but (1) I have a Lundahl with 250, 48, and 250 windings. My first inclination is to use the 250+250 and drop this (high-wattage resistor voltage divider? but would that be detrimental to the sound?) somehow; or I could use 250+48 and then a voltage multiplier - but again, sound quality. Or I could just run it at 300V...

And (2) how much bigger would the choke have to be? Kitic adds just one more 10H/50mA to the RH84 power supply, but I suppose would be prudent to add another choke and capacitor (CLCLC) - say 20H/80mA and 200uF on each rail (or do I really have to split the two B+ rails?).

Link to the schematic is here: RH 807 - Tube Audio ...... RH DESIGN
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Old 24th April 2011, 02:07 PM   #2
tim614 is offline tim614  United States
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When running higher voltage you need to adjust bias soothe tube doesnot fried,
As for the choke I would use a single choke 5-10h @ 200ma.
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Old 24th April 2011, 02:38 PM   #3
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Thanks, that will save a little money as well! Am thinking about 500R cathode resistor for the ECC81 and 2K2 for the KT66 but just guesstimates...
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Old 24th April 2011, 02:47 PM   #4
tim614 is offline tim614  United States
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You mean 500r for the kt66 and 2.2k for the driver
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Old 24th April 2011, 02:53 PM   #5
tim614 is offline tim614  United States
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If you would run this design @400v I would keep everything the same, I thnk it should be ok with 450-470r cathode r
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Old 24th April 2011, 03:29 PM   #6
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Ah! On Sarris's website the 6L6 runs at 320V with a 350R... 6L6 single ended tube amp | Tube amps DIY

The other very similar design that runs at 400V is the tubemaster sketch which has a 2K on the KT66 cathode: http://www.tubemaster.de/diy/KT66SE-DC.gif

So I think I'll go with your advice and run at 400, unmodified except to up the 6L6 cathode resistor to 470R and maybe add a capacitor to ground between g2 and the 10K.

Last edited by carbondated; 24th April 2011 at 03:41 PM.
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Old 24th April 2011, 03:44 PM   #7
BZed is offline BZed  United States
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These 2 designs are quit different. The 6L6 design is cap coupled on the out put grid and the KT66 is DC coupled. That is why the cathode resistors are so different in value.
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Old 24th April 2011, 03:56 PM   #8
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Thank goodness there are clever people to save me from myself!

I guess this would also explain why the KT66 design only produces 1.6W.
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