zero bias ef86

[Andy Le Blanc]

I'm trying to dig up RC amp data charts for EF86, anybody holding?

specifically for "zero bias" or "grid-resistor biasing", I'm old fashioned.

Equivalents are ....6267, 6F22, CV10098, CV2901, CV8068, Z729

0r even UF86 with the different Fil. v..

I can make an educated guess looking back and forth between RC charts
for AF pentodes that I do have sheets for both bias methods....
but why reinvent the wheel....

One thing I noticed with ef86 was the blow, and I've seen cheats where
the pentode is dress as a triode "just to get the tone", BS.....

The tube has internal shielding, one more internal element at ground
poteintial may quiet the tube, make for a simplified socket dress, and
another way to get more harmonic distortion and color.

[FUCHSAUDIO]

Andy, are you talking about grounding the cathode and applying negative voltage to the grid ? I may have curves home in one of my older textbooks if you don't find anything online.

[Andy Le Blanc]

Please....

its the old cap and leak resistor, with a cathode at ground potential.

A fixed bias chart would be very useful.

Alternative and out mode'd bias methods always have a much poorer
harmonic distortion figures, the color as a tone source is wonderful.

More along the lines of a "musical instrument".

[FUCHSAUDIO]

The tone change (I suspect) is a direct result of the elimination of negative feedback at the cathode. I would guess if you cannot find a curve chart, you could simply make a supply and start cold, say 20-V minus and reduce with a pot, just like a power tube biasing arrangement. Measure current on the plate load or in series with the cathode.....

[Andy Le Blanc]

I do have way to perform that, and dynamic tests, a way to get a distortion figure too,
I think I can also get a frequency response plot.

But I don't want to reinvent the wheel, the RC charts are based on a much
larger data set than I could ever hope for.

It may simply be that, that information doesn't exist because of when the
tube was developed, there is a historical drift of accepted practices,
for obvious reasons. You see 6SJ7 operated with grid leak in early PA, mic pre,
phono pre, etc.... and then after 40's, not so much. Fidelity rules.