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
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
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.
As for the choke I would use a single choke 5-10h @ 200ma.
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...
If you would run this design @400v I would keep everything the same, I thnk it should be ok with 450-470r cathode r
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.
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.
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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.
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.
I guess this would also explain why the KT66 design only produces 1.6W.
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