rjr@mgweed.UUCP (Bob Roehrig) (08/10/84)
I am going to modify an old grid-driven power amplifier, which has a pair of 4-400A's, to a grounded grid input. Has anyone used toroidal cores such as the Amidon T-200 (commonly used for baluns) for a filament choke? Most all units I have seen use a ferrite rod for this. I want this amp to go down to 160 meters. Many years ago I built an amp using a single 4-400A and used a rod for the choke. To get enough inductance to be effective on 80 meters, I had to wind 3 layers of wire on it and the wire had to be at least no. 10 to keep the voltage drop at a minimum. My old Hallicrafters "Loudenboomer" amp uses a tap on one winding of their choke to get a proper impedance match and I hope to do the same thing to eliminate the need for any input tanks. Bob K9EUI