[AMPS] al-1200

[Tom Rauch (W8JI)]

stratto wrote:
> 
> Last year at Dayton, I went by the MFJ booth to look at the al 1200. I
> noticed a difference in the al 1200 parasitic suppression choke
> coil/resisitor and also a small parastic suppresion metal strip besides the
> tube, about 1 inch long.

The strap is for neutralizing. 

There is a 180 degree phase inverting transformer under the chassis,
connected to the filament. The circuit samples RF near the anode by
capcitive coupling, inverts the pase 180 degrees, and applies it to the
filament (cathode). 

Heath and Gonset even used that system in some of their GG amps, and a
similar setup is used in the AL-811H.

No magic there, just a simple bridge neutralizing system.  

73 Tom



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