Transistor PA Biasing

by John Stockley G8MNY

Here is a simple circuit that can deliver the peak base current needed for linear SSB operation, that works very well. It uses 2 TIP type NPN transistors, 3 Rs, & suitable RF filtering for the band in use.

TR1 must be bolted close to the PA devices so that it's emitter base voltage can track the PA temperature, TR2 needs heatsinking so it is also convieniant to mount it close to TR1. Bias adjustment can be done by adjusting the 1K but never change it just for a preset without a min R!

The MAX base current, about 500mA is available, this is limited by the 22R & should be enough current for a 50W UHF/VHF or 100W HF PA.

73 De John, G8MNY @ GB7CIP

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