I have an Air King model 21 that I am trying to fix. The line cord resistance is unsafe due to badly frayed insulation. According to the schematic I have, the only difference between the model 21 and the model 22 is that the model 22 has a K90F ballast tube instead of the line cord resistance. In fact, the chassis of my radio was already factory-punched for the K90F socket. Only problem is, nobody has a K90F ballast tube for sale! My tube line up is: 6D6, 6C6, 38, and 76, and a #51 pilot lamp. How can I drop house current down to the appropriate voltage without excess heat? The radio has too little space to use power resistors - too much heat build-up. Help, please!

Brain fart - forgot I had already posted a couple of days ago. Still need help with this, though. I tried AES technical assistance, and they don't even have a universal tube that will work.

Check with Jim Cross at www.vacuumtubeinc.com He has lots of universals, He is showing an Amperite KL75H which is a universal for K 67 to 105 F This should work as your smack in the middle with your K 90 F.
See the this page for an explanation www.antiqueradios.com/chrs/journal/ballast.html