K3MSB

Keying Circuit for Cathode Keying

This circuit will work with positive voltages. I used an MJE13007G transistor as I had it in the junk box. It is rated at 400V / 8A.

My friend Dennis AE6C uses a TIP50, and R1 is 150 ohms. He uses a AAA battery.

Just about any NPN power transistor will do. For max Beta, bias so you're not in saturation.