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

[Bob Bruhns]

Hi Vince,

I have never tried these connections, but HLR-Timtron told
me the RCA trick with drive to the screens and a 20K from
the screens to the control grids was not ideal, and several
experimenters tell me there's no way you get 120 watts from
it at 750V.

Tim said that when you bias this arrangement and drive it,
first the plate current goes down at low audio levels, and
then it rises at higher audio levels, and he didn't like
that.  I forget whether he said there was distortion, but I
think he would have overlooked the odd plate current effect
if it sounded OK.

Tim used a different circuit. If I remember, he grounded the
control grids and drove the screens.  This makes sense to
me, but as I said I never tried it.  It surely must take
some serious drive levels, probably the screens run at
zero-bias and peak at +500V.  In the end, this all does
argue for 811As instead of 807s, if you have room for the
tube envelope.

  Bacon, WA3WDR
------------------------------

(original message)

Subject: [AMRadio] 807's triode connection question...
   Date: Thu, 4 Jul 2002 06:01:53 -0400 (EDT)
   From: <ka1iic at prexar.com>
     To: <amradio at mailman.qth.net>

Hi guys me again,

I've been looking up all the info I can get about using
807's in triode connection....

I have found 3 different cases and was wondering about the
benefits of each....

First off the older ARRL handbooks show connecting the grid
to the screen through a 20k ohm resistor and driving the
screen...

Another publication shows connecting the screen to the plate
directly and driving the grid as you normally would...

And case three shows connecting the screen to the plate
through a 100 ohm resistor and driving the grid as per the
norm...

Any guidance is welcome...  any comments welcome also...

Thanks in advance

73
Vince
ka1iic
-.--.