[AMPS] Re: New G2DAF amplifier information

[measures]

>
>> Not wishing to discuss the G2DAF circuit any further, I still want to
>> question your statement regarding substantial grid current causing
>> distortion.  I do not think that is necessarily true.
>
>Some tubes won't tolerate grid current, while many will. 

With the exception of the 4CX1000A's 0w grid rating, all tetrodes will 
tolerate some grid current.  The constant current curves show why you 
don't want any.  

>There are 
>dozens and dozens of tetrode types that can be run with a small 
>amount of grid current, and will give very good IMD performance. 

The 4CX1500B and the 4CX600J are two tetrodes that are designed to run 
with a tad of grid current in linear service.  Can you name another off 
the top of your head, Mr Rauch?.  
>
>The problem is not only anode current saturation, but it also 
>includes grid voltage to anode current change non-linearities 
>caused by grid intercept and other problems. 

agreed
>
>There also is the problem of a sudden change in grid impedance 
>with drive power.   

yea, verily
>
>AB2 SSB operation always requires a regulated low impedance 
>control grid circuit, and a well regulated screen supply of the proper 
>voltage. I do that in AB1 also, just to be sure if the tube is 
>"bumped" a bit hard it doesn't distort excessively.  
>
>I strongly question the wisdom of not only loading the exciter with a 
>changing impedance caused by control grid current, but 
>aggravating the problem by requiring the exciter to also supply 
>screen current through a rectifier system.

good points
>
>Maybe someone can explain to me how the screen voltage 
>remains exactly in phase with the driving signal, to prevent 
>envelope distortion from screen voltage shifting slightly out-of-phase 
>with drive?

BINGO.  Therein lies the third piece of specious logic in DAF theory.   
Congrats, Mr. Rauch.  
>
>Are tetrodes linear at all screen voltages with a constant grid bias?

To make it fly, one must have something close to the proper ZSAC  Screen 
potential has a very large effect on peak anode current and p out.  Grid 
bias is whatever it takes to stop the flow of grid current with max. 
drive applied -- unless of course, one needs to clear a proper swath for 
contesting.  .  
>
>
later, Tom

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


--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm