Hi,
I have cleaned the relays and I've had the amps services at a audio service shop. This works for a while but then they start to act up again and sound cuts in and out. Jiggling the front selector/mute switch takes care of the problem. But the bottom line is I don't want anything that is not needed. Best to bypass any areas of potential problems. Just need amp functionality! Don't mind DIY, as long as it's not a temporary fix, which cleaning the relays is.
well, there are no relays in the selector circuit, not on the original selector circuit. If proper relay were part of that selector, none of these issues would manifest.
The relays you cleaned or replaced, are located on the output to the speaker lines. Removing the relays, removes a very important function of the delay circuit that protects your speakers against transient currents during start-up. You could be frying a tweeter or two once in a while... Many commercial amplifiers lack the automatic delay circuits. Look at how the sound engineers deal with start-ups. I would personally not remove those relays.
back to the selector....
The selector also switches VCC for the A/B relays but if those contacts are bad, then the relay coil would not engage all together, so as long as you hear the relay click, the selector does a satisfactory job for A/B relay selector.
The problems you are experiencing are related to the input source selector lines. Here you are most likely dealing with issues related to oxidation deposits on the contact pads of the selector switches OR with degraded contact effectiveness of the potentiometers. It is usually BOTH.
These, if cleaned properly, would allow the amp to work for many more years. If cleaned with abrasive materials that remove some of the contact plating or create deep abrasions that limit the contact surface / contact effectiveness, then you end up with poor contact or no contact shortly after cleaning.
There is a way to by-pass the entire assembly, keep the pots and remove the switches, keep the switches and remove the pots, basically any combination you need. In this forum you should find the exact way others have done it.
There are a couple of very important variables to consider when sending a source signal straight to the driver boards and a third variable specific to B-2
1: you will have no capacitor coupling, thus not protected from DC coming down the line.
2: you will have high inductance coming through that line, thus unwanted noise if the line is not terminated.
3: specific to B2: if eliminating the rear RCA connection to the chassis, you need to wire the ground from the PSU board to each of the driver boards with a separate wire. This however has additional unintended consequences related to the original ground loop design (subject to more research and a broader topic).
side note: The selector assembly of the B-2 is it's Achilles heel. Instead of being fully eliminated and have a bunch of knobs and switches with no use, Ideally, the entire assembly would be redesigned and fitted with proper, hermetically sealed relays for source selector duty, in order to maintain all existing functionality but not suffer from any signal degradation.
Good luck with whatever you choose. The B-2 is one of the best sounding amplifiers you can find and worth bringing back to prime.