Geoff said: 75TH/TL, 100TH/TL, 152TH, 250TH/TL, 304TH/TL, 450TH/L, 750TH, 1000TH Mighty impressive line of triodes Eitel McCullough came out with. No doubt! I wouldn't mind having a rig that used either the 750TH or 1000TH! Now that would be impressive. The way I understand it that EIMAC first developed the 75TH for RADAR use during WWII. Mod-U-Lator, Mike(y) W3SLK