"6A10s are a good choice, but for a high bias tube like a GS-35b you need a lot of them - about 40. (24 VDC x .6 V per diode)." CW key up / key down regulation is not good with a string of diodes. With a dozen I measured a droop of 1-volt. With a 50 w zener it was nil. 73, Roy K6XK