I looked in all my industrial strength tube data sheet binders (GE, Wstgh. etc.) plus some old reference's and it's not mentioned anywhere. But we do know the amplification factor or mu (µ) is 160.
Gm = µ/Rp Therefor, if you figure the plate resistance for the circuit parameters used, you can compute the Gm.
To use round numbers, an Rp of 10K ohms would give a Gm 16,000 micromhos.
Gm = µ/Rp Therefor, if you figure the plate resistance for the circuit parameters used, you can compute the Gm.
To use round numbers, an Rp of 10K ohms would give a Gm 16,000 micromhos.
Hollow state astouffer has it right I can get a matched quartet of Chinese 811a or jans for cheap.
Funny you mentioned the 812a, that bad boys on my too do list of amps to build. But as for the application there isn't many other tubes that are affordable that will handle the current.
Originally I was plaining on using as 4-400 as the pass tube but I would be too close to the max dissipation to not forced air cooling, plus the filament transformer. The transconductance on the 4-400a isn't that high either.
Trust me I don't hold the 811a in low regard, it's just it fit's the application too well to pass it up.
Nick
Funny you mentioned the 812a, that bad boys on my too do list of amps to build. But as for the application there isn't many other tubes that are affordable that will handle the current.
Originally I was plaining on using as 4-400 as the pass tube but I would be too close to the max dissipation to not forced air cooling, plus the filament transformer. The transconductance on the 4-400a isn't that high either.
Trust me I don't hold the 811a in low regard, it's just it fit's the application too well to pass it up.
Nick
nhuwar said:
No Nick, I have not...not yet anyway. I have a good collection of 812s and a new pair of Electra Print 10K PP transformers that I got off eBay a couple of years ago. They are big and probably in the 50 to 60 watt range. In fact I have everything I need except time. Unfortunately earning a living gets in the way.
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