[AMRadio] 807's triode connection question...

[ka1iic at prexar.com]

Way cool Bacon thanks!

Yeah I want as little distortion as I can get...  I've got a half decent
driver all ready made up... all triode with a 6080 in push pull class A...
I gave it the old music test and it is really smooooooth...

I've got another set of tubes that I want to play with... 6384's... As you
know those tubes are 6AR6's with an attitude...  not unlike the 6L6 and
807's......   the 6384's have a max plte voltage rating of 750 volts me
think...

Any way thanks for the help... It's great to have FB OM's out there to
help this old timer along...

73
Vince
ka1iic
-.--.

On Thu, 4 Jul 2002, Bob Bruhns wrote:

> Vince,
>
> Since you're experimenting with 807s, here's something else
> to try.  It's not triode connection, but it does reduce
> distortion considerably, and it retains most of the high
> tetrode sensitivity of the tubes.  I have tried this with
> 6L6GCs and 8417s, so it should also apply to 807s.
>
> Connect the tube as usual for tetrode operation.  Supply
> screen voltage from a regulated supply.  But insert a
> resistor of about 5.6K in series with each screen grid, and
> do not bypass the screen.  That's two 5.6K resistors, one in
> series with each screen grid - NOT one resistor, then
> fanning out to both grids.  This is important for good
> results.
>
> When you do this, the screen voltage will be a little lower
> at high audio levels, so you might raise screen voltage 50
> volts or so, and adjust control grid bias accordingly.
>
> What I found was that resistance in series with the screens
> generally causes the transfer characteristic to curve
> downward.  The right amount of series resistance causes this
> downward curve to balance out the upward curve usually seen
> in tetrode and pentode amplifiers, resulting in much better
> linearity.  I found 5.6K to be optimum with 6L6GCs operating
> at 350V plate and screen voltage with a typical plate to
> plate impedance.  Other values may be optimum at different
> operating voltages and impedances.
>
> See also my articles on this subject in AM Press/Exchange,
> Issue 100, May, 1992 (Screen Impedance Negative Feedback),
> and Issue 110, March, 1994 (Improving the Linearity of
> Screen Grid Tubes), at www dot amfone dot net (not sure if
> url addresses get through here).
>
> OK, now it's time to go cook some hot dogs on the grill...
> happy Fourth!!!
>
>   Bacon, WA3WDR
>
> _______________________________________________
> AMRadio mailing list
> AMRadio at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/amradio
>