>..........
>
>........ The Care and Feeding of Power Grid Tubes that the screen
>voltage was constant. (Rich might say that they never thought anyone would
>be so stupid as to vary the screen voltage - making the test pointless).
? "shit happens" -- Forrest Gump.
>However, they do have an interesting comment in 4.4.4 (Effects of Screen
>Voltage) "... Usually, the lowest value of d.c. screen voltage compatible
>with a given power output will produce the lowest intermodulation
>distortion."
? As I see it, this means something different. To wit: when the screen
voltage is adjusted too high for the available drive available in AB1,
ZSAC increases unnecessarily. . To put the ZSAC right, one then needs
to increase grid bias beyond normal. This results in moving the
amplifier even farther away from the AB1 target of peak grid potential =
0v. In other words, the best way to adjust a class AB1 amplifier is to
adjust the grid-bias for virtually zero grid current - and then keep your
paws off. Screen potential is used to set ZSAC. However, the max.
screen potential rating should not be exceeded. .
>........
- Rich..., 805.386.3734, www.vcnet.com/measures.
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