Eiron references high-drool-factor circuits, was Re: Question about grid behavior with triodes


On Sep 29, 1:36 am, Eiron <E1...@xxxxxxxxxxx> wrote:
So putting 2V rms on the grid of a triode with a fixed bias of 2.4v
may not be such a good idea. Here's a circuit to experiment with -
http://members.lycos.co.uk/fiultra/BatteryT68bis.jpg

--
Eiron.

Dear Eiron is such a diligent student of my circuits and my netsite
but sometimes the pure size of it, the mountain of information,
overwhelms him. I'd quite forgotten the part-schematic he references
from my site
http://members.lycos.co.uk/fiultra/BatteryT68bis.jpg
which is part of a chapter in The KISS Amp on Battery Bias:
http://members.lycos.co.uk/fiultra/KISS%20126%20by%20Andre%20Jute.htm.

Complete high-drool-factor circuits with the same feature are here:
http://members.lycos.co.uk/fiultra/t68mzwe417acircuit.jpg
and here:
http://members.lycos.co.uk/fiultra/T39-KISS-300B-Ultrafi-crct.jpg
with discussion starting here:
http://members.lycos.co.uk/fiultra/The%20KISS%20Amp%20INDEX.htm

Those circuits are of course the result of years of study and
experiment; they are thus designed with the precise knowledge of where
the grid current kicks in objectionably in those particular tubes. As
I wrote to Wessel, following on from Patrick alluding to the necessity
of empirical tests: "It is useful to remember that, while we often
speak of grid current as if it is switched at the 0V negative bias
line, that is just shorthand. The onset of grid current is gradual and
starts on the right of the 0V negative bias line. Practically, in
small signal tubes, almost all high-mu tubes draw appreciable grid
current at about half-volt negative grid bias or more. Also, in SE
300B, it is foolish to run them with signal for the full negative bias
or even (as is often suggested) no nearer than the filament voltage to
the zero volts bias line; another handful of volts of restraining
distance will result in a much quieter amp: there is a reason why we
measure an amp's maximum output at the onset of grid current."

Congratulations, Eiron; it was most advanced of you to spot the
connection between that circuit and a heavy experimental schedule to
make and keep it kosher. I am always delighted when a student shows
promise. Young Eiron would probably appreciate a pat on the back for
his breakthrough from the other opinion-formers here on RAT.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
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containing vital gems of wisdom"
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