R: SV: SV: [AMPS] Final..

[measures]

>
>Once I've seen a grid driven amplifier in which a ferrite broadband
>transformer 50/200 ohm was used, probably to develop a bigger voltage across
>grid without increasing the driving power. The 200 ohm port, that one going
>to the grid, was also terminated in a 200 ohm non inductive resistor but its
>size wasn't sure good to dissipate large power 

The duty-cycle for SSB is pretty low, so the grid-termination resistor 
can be pretty smsll.  Another factor is that tetrodes with handles 
typically have much air going through the vicinity. 

>and was probably there to
>establish a load impedance, and nothing else.
>Personally I find quite useless to develop grid driven PAs if then a good
>linearity is only achieved lowering the gain to values typical of other, but
>much sympler, configurations (when tubes allows).
>Also dissipating the unnecessary driving power in a load before amplifying
>makes me thinking if the shortest line between two points is still a stright
>one.
>
burning up 1% of the RF is the price one pays for having a 20 db 
amplifier.  

ciao, Mauri
>
>-----Messaggio Originale-----
>Da: George T. Daughters <gdaught6@leland.Stanford.EDU>
>A: <amps@contesting.com>; <johnf@futurenet.co.za>
>Data invio: marted́ 4 gennaio 2000 10.11
>Oggetto: Re: SV: SV: [AMPS] Final..
>
>
>
>> My understanding is that one DOES NOT deliver power to the grid of an
>> AB1 amplifier.  The driving voltage is always such that the grid
>> is never driven into the region where grid current flows.  All one
>> does is charge and discharge the "input capacitance" of the tube.
>> If one refers to one of the ARRL handbooks, in the tube
>> charactersitics section, one finds "driving power = 0".
>>
>> So the grid of a tube biased for AB1 is NOT resistive.  A good way to
>> make the input of such an amplifier appear as a constant resistive
>> load to the exciter (a good thing!) is to put a fixed non-inductive
>> resistor from the grid to (RF) ground.  The resistor dissipates
>> (wastes!) the drive power.  Another benefit of such a resistor is
>> that it enhances the stability of the amplifier.
>>
>> 73,
>>
>> George T. Daughters, K6GT
>>
>
>>
>
>
>
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>


-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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