Hi All,
I recently acquired this Cary Audio SLA-70B and am really surprised at how good it sounds. I've had a couple of other Cary amps, and this one is the best of them. Anyway, the previous owner had broken a tube, and replaced it with a mismatch. I just plopped in a quad of cheaper chinese el34's to make sure it is up and running in good health. I went to bias the tubes, and discovered that the procedure outlined in the Cary literature doesn't work. The tube fuse has been completely bypassed somehow--you can remove the fuse, and the amp still runs fine. Upon internal inspection, it is obvious why--the fuse socket is disconnected. So that leaves me trying to figure out how to bias it. I have circled what I believe is the biasing pot in blue on the picture. I attempted to measure the current below the resistor that sits between the pot and where it is grounded on the capacitor, but could not get any current to register with the amp on and warm. Any guidance would be appreciated. I would also be interested in rewiring the tube fuse back into the circuit. --Jaybird
I recently acquired this Cary Audio SLA-70B and am really surprised at how good it sounds. I've had a couple of other Cary amps, and this one is the best of them. Anyway, the previous owner had broken a tube, and replaced it with a mismatch. I just plopped in a quad of cheaper chinese el34's to make sure it is up and running in good health. I went to bias the tubes, and discovered that the procedure outlined in the Cary literature doesn't work. The tube fuse has been completely bypassed somehow--you can remove the fuse, and the amp still runs fine. Upon internal inspection, it is obvious why--the fuse socket is disconnected. So that leaves me trying to figure out how to bias it. I have circled what I believe is the biasing pot in blue on the picture. I attempted to measure the current below the resistor that sits between the pot and where it is grounded on the capacitor, but could not get any current to register with the amp on and warm. Any guidance would be appreciated. I would also be interested in rewiring the tube fuse back into the circuit. --Jaybird