Not sure, see the parts about 2 new tubes from RF parts. Both faulty. Have to send them back for new. Input needs adjusting, but the tubes that came with it are dead. I may order a set off ebay, the chinese ones and try out. I did a string of 6A diodes, right around 4.2V or so. Then put a 50k resistor in series with that. Use a relay to bypass it in talk mode. Fuse bias, have a 10k resistor going across fuse it it should blow. Used a .5A resistor at moment. Input is definitely high, but I think that's because tubes were beat. Not gonna mess with until new tubes arrive. Guy that originally had it put over 150W into it until tubes gave up ghost.