[AMPS] SV: G2DAF and super cathode

[measures]

>
>One significant factor regarding the G2DAF is the time delay on the screen
>voltage.  If the dc created by the rectified rf charges a capacitor in the
>screen circuit and that charging causes a delay in the rise of screen
>voltage, then the screen will not be following the grid and distortion will
>occur.  So, if someone builds the G2DAF with a big screen bypass capacitor,
>it will distort.   This is a problem similar to alc circuit time constants
>which delay the gain reduction voltage from increasing until after "the bull
>is out of the corral".

€  This is the tip of the iceberg.  What about the seriously non-linear 
relationship between screen potential and peak anode current?.  
>
>The RCA Transmitting Tube Handbook shows a recommended Class B circuit which
>connects the screen grid to the driver transformer and the control grid
>through a resistor to the screen - thus operating the tube as a triode.  In
>this case, the screen voltage is not regulated - yet the stage is linear.

If this is the case, there can be no grid/screen amplification.  At RF 
frequencies such a circuit is quite like to result in oscillation.  

>So to categorically dismiss the G3DAF as a bad circuit because the screen
>voltage is not regulated is in conflict with RCA's recommended circuits -
>and they pretty much wrote the book on vacuum tubes.

RCA does not recommend a circuit that is anything like the DAF design.  
>
cheers, Colin

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


--
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