Question about 1/2 power switch
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- flatfive
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Question about 1/2 power switch
I've tried to understand what's being said about this modification. Someone suggested a layout which I'm enclosing. From what I understand, it lifts the ground of two of the cathodes. Is this correct, and are there problems with doing this? Do you have to change the impedance?
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Yes, it lifts the cathodes of one pair of tubes. Rather than disconnect their cathodes from ground, I prefer to run them through a 10K 2 watt resistor to ground, this effectively cuts them off and the trickling current through the 10K cathode resistor keeps the tubes happier.
I would change the impedance, though I think others have reported no problems when they didn't.
I would change the impedance, though I think others have reported no problems when they didn't.
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- markh
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1/2 watt might be a bit light. You could try two 22k or 33k 1/2w in parallel or two 4k7 or 6k8 in series.
I don't worry about impedance at half power.
--mark
I don't worry about impedance at half power.
- - The circuit is spec'd for twice the power you're using, so there in no real strain anywhere
- The reason you're doing half power is you *want* it to be quieter. Mis-matching the impedance reduces output power even further.
--mark
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- zaphod_phil
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It helps prevent cathode poisoning, which happens if you run a tube heated but with no voltage across it for very long. There are probably some other good reasons which I can't think of right now....creeble wrote:I-- not exactly sure why having some current flowing is better than none?
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Nature abhors a clean tube amp
- TDuly
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Well, there are many production amps using the half power cathode ground lift without it so 6 of one and a half dozen of another your mileage may vary.zaphod_phil wrote:It helps prevent cathode poisoning, which happens if you run a tube heated but with no voltage across it for very long. There are probably some other good reasons which I can't think of right now....creeble wrote:I-- not exactly sure why having some current flowing is better than none?
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