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In Reply to: RE: update.... posted by vinnie2 on February 12, 2019 at 14:57:38
The amount of drive you need for the 845 is way more than for an 813.
Follow Ups:
Are you sure? What's the mu of the 813 in triode mode?
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Buy Chinese. Bury freedom.
But in pentode the manual says, "Because of its high power sensitivity, the 813 requires very little driving power to give full power output."
Although, i recall running across somebody drew load lines for triode connected. I did not save that link. It might have been on this forum.
Pentode sensitivity is irrelevant. I thought maybe you knew what it was in triode, based on your comment. The two tubes are probably similar when both are triodes.
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Buy Chinese. Bury freedom.
Edits: 02/13/19
Looks like a mu of about 7 to me.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Honestly, using hand-drawn curves like those to design an amp is worse than just picking some random schematic off the 'Net and building it.
That graph is from Andrea Ciuffoli's site. There are two more; one highlights amplification factor (7.7), and the other shows gain with a 10K load (6.6). Again, I'm skeptical of the accuracy of things like this, even when they come with reasonably good credentials. In this case, I'm particularly bothered by what appear to be several mis-starts in the curves. There's just no substitute for data taken in a laboratory environment using calibrated equipment.
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Buy Chinese. Bury freedom.
I need to check my notebooks. I think I have a drawing of plate curves for a triode connected 813 I found a while back.
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Thanks Buffy! I think that is the same one I have someplace, but now I won't have to dig it out.
Guess I will just have to do the substitution and see what happens.
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