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In Reply to: RE: VR Tubes in Commercial Amps posted by Triode_Kingdom on October 21, 2016 at 09:22:11
Almost all tube type Leslie amps (for organ) use them for screen reg.
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Leslie amps use the VR tubes as a fixed voltage drop from the B+ to the screens. The screens are only regulated relative to B+, not to ground or to the cathodes. I'm not sure how this affects the sound, or if it even qualifies as screen regulation. Pretty odd arrangement. Any thoughts on this?
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Buy Chinese. Bury freedom.
Edits: 10/22/16
I've services hundreds of those, but never noticed the VR tube is in series with the screen supply.There used to be a mod some people did on Dyna ST70's and HH Scott integrated amps where a diode was placed in series between the plate supply and the screen supply. The idea was to prevent the front-end supply from collapsing when the plate supply sagged under load.
I wonder if that was their intention?
Can a VR tube act as a diode?
Edits: 10/23/16
I didn't realize the Leslie amps were like that either, but then I looked up the schematics as a result of this thread. Sadly, both of mine are solid state. Anyway, the series VR is acting like a Zener, not as a forward biased diode. The B+ would have to sag a lot to create the effect you're describing, enough to extinguish the tube.
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Buy Chinese. Bury freedom.
AFAIK, these are important for non-distorted bass. They are hardy souls. Never had to replace one. Of course, only worked on two Leslies, in my life.
Need to restore one of these, someday.
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