Some time back in the 70’s, I was at the old Wine Cellar in Longmont, Colorado listening to my good friends Casey Anderson and Bill Wienacht sing and play. I had recorded Casey many times and sold cassette tapes at his shows, but this night I was just relaxing and enjoying his music. Funny, I had recorded his songs and produced cassettes, so I probably heard every one of his songs over a hundred times, if not more. Yet I still enjoyed going and listening to him on “my night off” because he was such a great entertainer.
I was there with friends including the lady who would become my wife. Part way through the first set, Casey’s amplifier started cutting out. After a little pause and maybe a little swearing, he plugged into Bill’s bass amp, and the show went on.
During the next break he asked if I might take a look at his amp. “Casey,” I said, “you don’t get it. To troubleshoot problems I need tools and meters and maybe even a scope or signal generator. Plus, if I could figure out the problem, where would we get parts in a middle of the evening in a bar?” But Casey had confidence in me, and said, “I’m sure you’ll figure it out.”
I had noticed it was cutting on and off and so maybe the problem was something was loose. I looked into the back and noticed the tubes were not lit up. No power. I then noticed that the pilot light wasn’t on. So that was the problem. I checked the fuse, but no joy; the fuse was good. I switched power cords with the bass amp and confirmed there was AC power. Without a meter, I didn’t think I could do much more, but I figured I might as well drop the chassis out and take a look.
Fender guitar amps have a metal chassis, which is basically a rectangular box made out of sheet metal that is open on the bottom. Only, on the Fender amplifier, it is screwed to the top of the wooden case and speaker cabinet with the open end up, sort of upside-down. In the front, the chassis has the knobs, input plugs, and the pilot light that wasn’t lit. In the back are a few more plugs and switches, and the tubes are mounted pointing down, hanging into the speaker area. On the top are four screws that attach the chassis to the wooden case.
I took out my trusty pocket knife, and using the screw driver blade, I dropped the chassis. Logically I started with the pilot light. (That isn’t logical at all, but it did seem like a good place to start.) The pilot light is a low voltage bulb, typically six or twelve volts. It runs off the same transformer winding that provides the filament power to the vacuum tubes. The filament is exactly like the part of a regular light bulb that gets hot and gives off light. In a vacuum tube, the filament heats up the cathode to create free electrons, and that is the way a tube works. That is why tube radios and amplifiers have to warm up a bit before they play. The filament has to get hot, heating the cathode, and forcing it to emit electrons. The filament runs off a winding from the transformer which provides twelve volts to tubes like 12AT7 (that’s what the 12 stands for, filament voltage) or 6L6 (which uses 6 volts). The pilot light was in a little plastic socket with two small eyes at the end to attach the wires. That is where the power was connected.
Now think about how you might wire up your house. You could run a cable (wires) from the main power panel to the first receptacle in your house. Then run a second cable from the power panel to the second receptacle. And repeat that for every power receptacle in your house. But that would take a lot of wire. Instead of wiring each receptacle and switch box from the main panel, what the electrician does is run power to the first receptacle with a cable from the main power panel. Then he (or she) runs a cable from the first receptacle to the second receptacle, and then from the second to the third. I’ll bet you’ve opened up those receptacle boxes and you may have noticed there are always two cables running in. (Actually four wires, two white and two black … plus a green ground wire. But anyway, there are wires both into and out of each box except for the last box in the circuit.)
Well that is how Mr. Fender had wired this amplifier. The power came to the pilot light and from there it went to each tube socket to provide filament power. And guess what! The wire was broken loose where it was soldered to the pilot light socket. Most likely it was a bad solder joint from day one, but it was stuck in the hole and worked. It had finally wiggled out to the point that the connection was broken. If I had used a meter, I would have seen that the other voltages were present, only the filament voltage was missing. And without a hot filament the tubes didn’t work and neither did the amp.
Now I knew what to fix, and it wouldn’t need a part. Just a soldering iron and some solder. I asked the bartender if he had a soldering iron. After the surprising response that he didn’t, I realized a quick trip home was in order. I told Casey to extend the break a few more minutes and I would be right back. I rushed home and grabbed my soldering gun (no time for an iron, and the gun would work OK on the large pilot light terminal) and a spool of solder and I rushed back.
By now the patrons were a little antsy. They wanted to hear Casey play and didn’t understand what I was doing up on the stage. I quickly resoldered the connection and didn’t even bother screwing the chassis back in. It hung in place well enough that Casey could plug in and start playing.
As he started into his second set, I sat down for a cold beer. Suddenly Casey stopped playing in the middle of his first song, and quickly explained that I had fixed his amp, and the show would go on. As he pointed me out back at my table, the joint broke out into spontaneous applause. I stood to take a bow, and everyone jumped to their feet in a standing ovation. (At least that’s how I remember it, and nobody can say different. That's my story and I'm sticking to it.)
I never charged Casey for the repair. He was a personal friend, and besides, the applause was really more than I had ever gotten for any other repair in my life. To this day when I do a “real good spreadsheet,” I look around to see if anyone noticed. Maybe I could get a little applause! Or maybe I just need an audience here in my office!! I could serve drinks!!!