EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: ELS122 on October 03, 2022, 10:00:06 pm
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I can't find this listed in datasheets, only the pentode anode impedance.
I'm specifically looking for a 6AS6 tube wired as a triode, with the suppressor at 0V
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Why 6AS6 in particular? It’s main design merit is to use the screen grid and suppressor grids for additional control / mixing / gating. A pentode like EF86 works well as a triode connected.
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Why 6AS6 in particular? It’s main design merit is to use the screen grid and suppressor grids for additional control / mixing / gating. A pentode like EF86 works well as a triode connected.
because I need to use the supressor to adjust gain
and in my design a vari mu triode wouldnt be ideal
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My guess (not having done the full analysis) is that for a 6AS6 with screen connected to plate, varying the suppressor voltage would change the transconductance more than changing the mu, which is (roughly) governed only by the geometry of the tube.
This, of course, would change the plate resistance of the resulting triode.
Practical variable-mu triodes (or pentodes) have a non-constant grid-1 winding pitch along the length of the grid, and the result can be considered as low-mu and a high-mu triodes connected in parallel.
As the grid-cathode voltage becomes more negative, the high-mu triode cuts off earlier, leaving the low-mu triode active, creating the variable-mu effect.
Page 4 of the GE data sheet https://frank.pocnet.net/sheets/093/6/6AS6.pdf gives rather complete curves of the plate current and screen current as a function of suppressor voltage, along with transconductances.
You should be able to calculate the overall anode resistance from the plate and screen currents graphed on page 3.