harddriver
Well-known member
Hey guys after a long time I finally finished my 1969 Super Bass build, it has a Metro chassis, period correct fiber circuit board and NOS Iskra reisitors and NOS mustard caps. I formed all the caps while bringing the amp up to line voltage on a variac. All the voltages fall into line except the V2 Pin 1,7,8 voltage is about 30 DCV too high at 205 DCV, this is the cathode follower tube with the 100K resistor from pin 6 to 1 and then pin 7. The Normal spec voltage rating for V2 on a vintage 100 watt Marshall is supposed to be, pin 1 168 pin 6 303 pin 7 168 pin 8 168 according to voltage charts I have. I thought the vintage Iskra resistor might not be dropping the B+ from the rail correctly so I changed it out with a modern 100K and it had the exact same reading. Should I up the resistor to to 150K or so to get my V1,7,8 closer to spec or live with it? From my other readings the 100K should be giving at least a 100 DC volt drop Anyway took some reading from the incoming B+ along the dropping resistors to the B+ rails to the preamp tube sockets to give you an idea of the overall voltages. the amp plays and sound great, I did try a 12au7 in that position and the Pin dropped to like 111DCV on pin 1,7,8, but it sounded like shit but the it dropped the votage.. Could the preamp tube itself be causing the voltage shift?, I used good JJ12ax7's on the iniital start up after cap forming. Here's what I have for voltages interested in your thoughts o the matter. The AC line voltage was swinging yesterday due to grid load so the ACV line in was 115 to 118ish. At 123ACV the B+ is a healthy 491DCV.