Hi!
Could somebody please help me understand the u parameter for pentodes as specified in datasheets? I see this:
I tried googling, but failed miserably 😳.
Thanks!
Jose
Could somebody please help me understand the u parameter for pentodes as specified in datasheets? I see this:
I tried googling, but failed miserably 😳.
Thanks!
Jose
Correct, which is effectively the same thing as the triode mu.
Does that mean a sweep tube like 6AV5GA with a "triode amplification factor" of 4.4 needs only 4.4x the voltage swing on the screen as the grid? I've always wondered about adapting a modular amp for screen drive.
In triode mode G2 is connected to anode, so there is no control voltage at G2.
That (4.4) simply means that as a triode, the amplification factor of 6AV5 is 4.4.
That (4.4) simply means that as a triode, the amplification factor of 6AV5 is 4.4.
Roughly. More like: if G2 is at 150V, and you swing G1 from zero to -34V, you swing from full-on to full off (cut off). Except nothing turns off abruptly, so you are likely to have to swing 1.5X even 2X the nominal "cut off" G1 voltage. But working in class A you never want to get near cutoff (b/c gain falls off and wave is flattened), so uG2-G1 is a useful number.
ALSO the maximum current is less if Mu is high. That's why the brutal sweep and RF tubes run low Mu(g2-g1). This may mean awkward partial supply voltages. "For audio" tubes do not need HIGH current but instead are trimmed for Vg2 nearly as high as Vplate (or with crystal diodes, Gg2 may be half of Vplate, see 6550). OR in parlor radios, the RF/IF/1stAudio/Eye stages ran 250V, so Vg2=250V may be a happy condition even with plates at 300V or more.
Interesting. I strap them (sweep tubes) as triodes so G2 is slightly lower than plate (240R screen stopper). There's really no "real" triode that can compare.
I have always taken this number to mean the Mu of a multi grid tube when G1 is the controlling grid and G2 is used as the plate. This was the preferred method for measuring Mu of a triode strapped pentode as it takes the effects of G3 or the beam plates out of the equation. This belief comes from somewhere deep in my past and I cannot find the reference via Google either. Multiple search strings lead to all sorts of unrelated information about gravity and vibrational motion. I did find a short reference to a Morgan Jones book with a couple paragraphs of info and a link to buy the book. I have them in a box somewhere, so that could be the original source of my belief.
I also found this link via Google which sheds some light as to why measurements with G2 as the plate vary less than straight triode strapping:
http://www.r-type.org/addtext/add002.htm
I also found this link via Google which sheds some light as to why measurements with G2 as the plate vary less than straight triode strapping:
http://www.r-type.org/addtext/add002.htm
I looked at a 7591S data sheet.
It lists u = 16.8
Looking at the Triode curves, I drew a line at a constant 'plate + screen' current = 60 mA, then . . .
For g1 voltage ranges of: 0V to 5V; 5V to 10V; 10V to 15V; and 15V to 20V, the plate voltage changes by 80V.
80V / 5V = 16.
Triode u = 16 from the curves
That is awfully close to the specified u = 16.8
Just one example, for what it is worth.
It lists u = 16.8
Looking at the Triode curves, I drew a line at a constant 'plate + screen' current = 60 mA, then . . .
For g1 voltage ranges of: 0V to 5V; 5V to 10V; 10V to 15V; and 15V to 20V, the plate voltage changes by 80V.
80V / 5V = 16.
Triode u = 16 from the curves
That is awfully close to the specified u = 16.8
Just one example, for what it is worth.