[Amps] Tyning a $CX250B Amp ( was No Subject )

[donroden at hiwaay.net]

Replying to this subject, I was using a small phone and took shortcuts  
that I may have wrongly assumed were a little clearer than actually  
written.


" Remove the connection between the tubes and the plate cap and see if  
the tubes are stable by themselves" ....

Should have read, " Remove the connection between the tubes and the
PLATE TUNING CAPACITOR  and see if the tubes are stable WITH ONLY  
PLATE VOLTAGE AND SCREEN VOLTAGE APPLIED  ( proper bias of course )  
and NO RF DRIVE."

At just enough bias voltage to start drawing plate current, move the  
pi-network plate tuning capacitor and plate loading capacitor through  
all possible combinations.  If you don't see a rise  in plate current,  
change the bias voltage to draw 100ma per tube and again, rotate the  
plate tuning and loading capacitors through their range.

If the tubes are DC stable at this point,
THEN set the bias to a low value of plate current and slowly apply RF  
to the input with the output into a 1KW dummy load.

Get the amp stable with only DC before applying RF drive.

Sorry for the confusion.



Quoting donroden at hiwaay.net:

> If you have under 200 ohms hung off the grids , a quad won't turn  
> into an oscillator.   Remove the connection between the tubes and  
> the plate cap and see if the tubes are stable by themselves
>
> Don  W4DNR
>