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In Reply to: RE: Only later variants had higher ratings posted by PakProtector on April 22, 2021 at 09:19:35
Guess I haven't seen those. The 6L6GB types in my stock look like 23W tubes. The anodes aren't as large as the GCs.
To tell the truth, I'm not too concerned about the issue of screen voltage from the standpoint of ratings. I'm using VR tubes in series from the B+, so the actual voltage at the screens can be adjusted merely by plugging in a different VR. I'm more concerned about distortion at various screen potentials. I'm surprised this topic isn't better represented in technical publications online. Maybe it's in one of the RCA publications...
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Buy Chinese. Bury freedom.
Follow Ups:
The distortion performance is not due to g2 voltage, but what g2 voltage does to the performance envelope, and where the load line is driven across the characteristic plate curves.
It could be this was treated as 'everybody knows that' sort of topic, and therefore effectively ignored.
Call up a solid data sheet, likely a GE one, and for a given idle point, examine what changing the g2 voltage does to the load line location. Stay entirely resistive( a straight line, not an ellipse) and examine a 6CL6 data sheet. I have no doubt the lesson is transferrable to your 6L6 work.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I've always believed screen current introduces its own non-linearities, and that this modifies the optimum ratio when looking at small-signal distortion. Given the vagaries of real world loads, this might be too minor to be worth pursuing. I'll just use the loadline as you suggest and maybe adjust the screen voltage empirically after the amp is built.
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Buy Chinese. Bury freedom.
Seems like a plan; the 'bunching up' of the plate curves at low current( gm shrinkage ) is unavoidable. Driving the load line through the knee where they bunch up again is avoidable.
I put together a 6AV5 pentode linestage once. g2 at 75V, B+ about 250 and filtered the heck out of the B+. Ran a 510R load, idling at 50 mA. Nearly vertical as far as the tube was concerned. That load line went nowhere near the knee, and it sounded quite good( as well as letting me use a 0A3 to shunt reg the g2 supply ).
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
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