[Amps] 810 Linear Amp

[Carl]

That really has no bearing on typical old technology ham tubes.

A lower gain tube requires higher negative bias in order to maintain a 
reasonable ZSAC. It then requires sufficient RF to overide that bias.

You can easily compute the power required in Class B GG as well as the 
low driving impedance, both of which require real power to overcome. 
Many tubes dont have the grid dissipation available to do this.

Carl
KM1H



----- Original Message ----- 
From: "Bill Fuqua" <wlfuqu00 at uky.edu>
To: <amps at contesting.com>
Sent: Wednesday, March 11, 2009 4:56 PM
Subject: Re: [Amps] 810 Linear Amp


>   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 at sympatico.ca>
>>To: <amps at 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.
>> > _______________________________________________
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>> > Amps at contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>>
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