Triode tubes don't have to have high mu to be operated in grounded grid.
You may loose a little power gain but
not necessarily as bad as you many think.
Here is a fine example
http://www.mif.pg.gda.pl/homepages/frank/sheets/088/3/3CX10000A3.pdf
3CX10,000A3 has a amplification factor of 20. But in class AB2 grounded
grid operation its power gain is
about 10 db. or factor of 10. Even in class C grounded grid it is not so
bad.
The high mu tubes allows you to operate zero bias or nearly zero bias
with a bit more power gain.
Also, the input impedance is higher.
This is an EIMAC data sheet. I am not making this up. As I had said in
before. One of my early amplifiers
was a pair of 250TH tubes which were not particularly hi mu tubes (37).
drove them with a pair of 6146B's and
at a full gallon in the 60's. I am glad that I did not know then that low
mu tubes could not be used in
grounded grid. Strangely enough, the 250TH was considered hi mu by EIMAC
then. H was for high and
L was for low .
I believe this idea may have started back in the transceivers could not
drive high impedances and
many grounded grid amplifiers did not have impedance matching networks in
them. That is just a guess.
With a amplification factor of 36 I would not be surprised that you
could get 1000watts out with 100 watts drive.
You may not get a full gallon but I don' think you need several hundred
watts to drive it.
73
Bill wa4lav
At 04:11 PM 3/11/2009 -0400, Carl wrote:
>With only a mu of 36 you would need a couple of 811's to drive them and
>the voltage swing needed would have them sounding like a CB amp.
>
>Great Class C RF or B modulator tube. I use a pair as modulators for one
>of the big old style amps here.
>
>Carl
>KM1H
>
>
>----- Original Message -----
>From: "George Knight" <gkve3ltu@sympatico.ca>
>To: <amps@contesting.com>
>Sent: Wednesday, March 11, 2009 3:15 PM
>Subject: [Amps] 810 Linear Amp
>
>
> > Hi All,
> > I am considering using four 810 triodes parallel connected in a
> > grounded grid amp. Plate voltage would be about 2500 v. and expected
> > output power should be close to a kilowatt. Has anyone in the group
> > made such an animal, and if so, how did it turn out and what pitfalls
> > should I avoid? Any info on operating parameters such as bias would be
> > very welcome.
> > Thanks and '73 ,
> > George, VE3LTU.
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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