[AMPS] Screen voltage effects???

[Randall DuCharme]

--- Lamb <k7fm@teleport.com> wrote:
> Very few tubes have published screen voltage curves
> showing what happens
> when you change screen voltage on a particular tube.

I'm glad I'm not the only one experiencing difficulty
in finding data.  :-)

> The very few curves that are published lead me to
> conclude that varying
> screen voltage within a range of 25% to 100% of
> maximum will be fine, with
> the understanding that gain will increase as screen
> voltage is increased.
> When the screen voltage is run below 10% of rated
> maximum voltage, strange
> things can happen.  I would be very concerned about
> distortion products and
> other undesireable characteristics under those
> conditions.

I guess I never intended to drop to a level as low as
10%.  I was more interested in the effect of the
scenario where I decided to run it class C for some
hi-power CW operation or something but left the screen
volts at the AB1 level. ( 750 V as opposed to dropping
it to 400 )  If the only difference is higher gain....
that doesn't sound all that bad to me :-).


> And, be sure to use a regulated screen voltage.

I will for sure though for the 813 project I intend to
use VR tubes.  Partly because they're of the same
'vintage, as the 813s, partly because I've never
messed with them, but mostly because I have a metric
@$*tload of them.  What I can't decide yet is if I
need choke input screen & bias supplies or if cap
input will be adequate.  Further, whether I should use
some sort of series or shunt regulation techniques as
well.


Lots to ponder, lots to play with.  Thanks to all
who've shared and helped me thus far!

Randy (AD5GB)


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