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In Reply to: RE: I know I sound like a broken record posted by BofService on April 09, 2015 at 08:20:31
Since the two sections of each rectifier are paralleled, the min series impedance is 75 ohm, not the 150 from the chart. The stated sec resistance on the schematic is ~40 ohms so internal impedance is still less than spec. One detail often overlooked is that the primary resistance as reflected to secondary should also be added in to the meas secondary resistance. In this case it might add 10-20 ohms to to the 40 already present. One possible solution would be to add say 20-50 ohms resistor to each sec winding. Another would be to add an NTC IRL to primary for added reflected impedance.
Follow Ups:
"add an NTC IRL to primary for added reflected impedance."
Might not be the optimum solution... he did say the flashover occurs 8-10 seconds after power on. The fixed resistors you suggested would probably work, and I think he should try a different brand of rectifier tube as well (per Jim's advice).
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Buy Chinese. Bury freedom.
Flashover occurring 8-10s after power on is about when the tube begins to conduct. At this point the IRL will still possess considerable resistance because it's not fuly warmed up. Whether or not this prevents startup flashover using substandard rectifiers is unknown. But there are other benefits even if it doesn't prevent the flashover so it would be one of the first measures I'd consider if the amp were mine.
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