I picked up a 1970 Super Reverb about 8 months ago. The previous owner said that he "Blackfaced" it and, as a bonus, used 12 gauge solid core Romex Electrical wire for the speaker wiring. Being cautious about "mods" that others have done I inspected the board work, which was good and the speaker connections. The joints looked pretty solid. About 2 months ago the sound quality declined considerably. I put new power tubes in and rebiased. I was still getting strange harmonic overtones. Changed out the preamp tubes- same problem. Got busy and didn't take up the problem until last week. While playing through it the sound suddenly cutout. I immediately powered off and checked the fuses, tubes, etc. and then decided to pull the chassis. While removing tubes I noticed that one of the speaker wires had broken off of the joint. I rewired with 16 ga. stranded and the amp never sounded better. Fortunately I didn't toast anything and had improved tone. I believe that the reason stranded wire is used is so that it flexes under vibration. I've wired much Electrical machinery and have used stranded wire for this purpose. The original owner said that he read in a "well known" amp modification book that this would give a great improvement to the tone due to more signal hitting the speakers with less resistance. I hope that this is not true as I could have lost a great amp due to a bad idea. Maybe this will help someone else to save their amp from blowing up.