I was wanting to get something from my late friend Charles Kittleson's estate sale on the auction site; wound up with a Knight KB-85. Researching it I noted that many people were subbing 6L6 types for the rare EL-37s originally used. However the tube manuals indicate that the EL-37s were replaced by EL-34's. Sure enough the ratings are virtually identical. Triode electronics had the schematic; it is the classic 5-20 x 2; in fact there are 10 tubes on the amp. This is NOT your Stereo 70; the transformers are HUGE and it has dual rectifiers and a choke filtering the B+. Whoa the fuse was missing; but oh well lets stick a new one in and crank the Variac. 490 volts on the plates, and the bias was spot on the schematic values.
Plan is to re-cap it anyway; with snap-ons for the plate supply and a couple of PCBs mounting the smaller caps. Will run the stock circuit and get baseline measurements but that huge dual 5AR4 power supply is just begging me to run 6550s fixed bias from a low mu phase splitter.
Plan is to re-cap it anyway; with snap-ons for the plate supply and a couple of PCBs mounting the smaller caps. Will run the stock circuit and get baseline measurements but that huge dual 5AR4 power supply is just begging me to run 6550s fixed bias from a low mu phase splitter.