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previous: A.Colman Thanks to J.Burt,K.Bull,Jon & SG fo... -- 10/18/2000 1:04 AM

Re: 7868 to 6L6GC conversion

10/18/2000 3:52 AM
jon	Re: 7868 to 6L6GC conversion A., I'd start with 25uf. You want the cap to be rated for at least twice the voltage you expect on it. A 100V electrolytic would give you way enough safety margin, you should probably be able to use one rated less. If you want tighter low end, increase the uf value of the cap. You probably won't hear much of a difference above 100 uf, but the power supply design (tube rectifier?) will also contribute to response. BTW with the proper choice of cathode resistor, you should be able to run either 6V6 or 6L6's at 420 plate volts, if they're good NOS tubes. Run the screens some 10 or so volts lower and you should be OK. Chinese 6V6's probably won't like this circuit too much if you're biased warm. Check how close to 6.3V AC you are if running 6L6's. If your more than 10% below, probably should think about an additional filament tranny or some other way to free up some AC, such as changing the pilot lamp. If the tranny is too hot to handle after a 1/2 hour, you're probably taxing marginal iron and should think about an upgrade. As a rule, I don't keep any of the later Bogen power trannies on board, usually sub in bigger iron. hope this helps, Jon

10/18/2000 3:52 AM

jon

Re: 7868 to 6L6GC conversion

A.,
I'd start with 25uf. You want the cap to be rated for at least twice the voltage you expect on it. A 100V electrolytic would give you way enough safety margin, you should probably be able to use one rated less. If you want tighter low end, increase the uf value of the cap. You probably won't hear much of a difference above 100 uf, but the power supply design (tube rectifier?) will also contribute to response. BTW with the proper choice of cathode resistor, you should be able to run either 6V6 or 6L6's at 420 plate volts, if they're good NOS tubes. Run the screens some 10 or so volts lower and you should be OK. Chinese 6V6's probably won't like this circuit too much if you're biased warm. Check how close to 6.3V AC you are if running 6L6's. If your more than 10% below, probably should think about an additional filament tranny or some other way to free up some AC, such as changing the pilot lamp. If the tranny is too hot to handle after a 1/2 hour, you're probably taxing marginal iron and should think about an upgrade. As a rule, I don't keep any of the later Bogen power trannies on board, usually sub in bigger iron.
hope this helps,
Jon

Replies:

A.Colman By the looks of it another possibil... -- 10/18/2000 1:15 PM