This may be a bit far out, but we've seen it happen before. Did you hook up the speakers correctly. The 555a and it's older colleagues hooks up with left/right on top of one another, not side by side. Adjusting is certainly something you can do - much easier than the recap. Bias is measured across fuse holder with fuse out - measure in mA !! I think it's 20mA, but verify. As smurfer77 mentioned, this is not a DC amp, but capacitively coupled. For that reason you don't adjust DC offset as usual. Now, you can still measure the off-set by probing the speaker terminals, but only with speakers ora load resistor connected. This exercise will give you some idea of the health of the amp as well as the coupling caps. Look for 5-10mV . As for adjusting DC-offset, or " centre voltage" as the manual calls it. You need a scope, but can still get a useable setting by measuring DC voltage at the supply cap, then divide by 2 and then probe the coupling caps plus side to chassis ground and use trimpots to set to the 1/2 value.