Go To:

Home page

Amp Repair

Amp Tubes





Advice I got from an old operator about 20 years ago, and it is especially true today. Like anyone else who works on jukes, I have accumulated a pile of junk. Most of it is amp chassis that have been picked clean to repair other amps. I never gave much thought about them until the past year or so when amps all of a sudden were becoming hard to find.


I had a customer in Little Rock who sent in a 2300S amp for repair. It is a 2-piece amp, the power supply being on one chassis and the main amp on another. The power supply arrived, the main chassis didn't. After a week of trying to get the post office to find it, we gave up and he started looking for another chassis. There wasn't one to be had anywhere. He called and called and couldn't find one.


After a couple of weeks he gave up and asked if I could help. Sitting in my store room was a junk chassis that had been picked clean. Practically everything that could be removed had been, but it looked like this was the only way out. So I started trying to reassemble the remains. A day later, and no telling how many new parts, it came to life.


Now this may be an extreme case, but it did teach me a serious lesson: some jukebox parts are simply not available anymore. What may have been trash 5 years ago is now a valuable part! When I think back about the amps I've carted to the landfill, it makes me sick. But after all, that was IO or 20 years ago, and they were plentiful then.


Not long ago I got a call from a person in New York. He has a Seeburg B, which had a bad speaker. He stated that he went to Radio Shack and bought a 15" speaker which he installed in his juke. Now, on bass notes, the juke sounds "boomy," and has very little high frequency response. He said that it sounded like one of the low riders you see on the streets. What could he do to correct this problem?


The original speakers in jukes are paper coned. The edges are made from the same material as the rest of the cone. This is for a number of reasons, one of which is to limit the travel of the cone in and out. Also, this makes the cone stiffer, which helps with the high frequency response.


His speaker had a foam edge, which maximizes low frequency response. The cone travels so far in and out to increase the bass, that it cannot correct itself to property respond to the higher frequencies.


The bottom line is this: you cannot use a foam edge speaker in a jukebox. All you will have is low frequency response, and it will be hard to keep the bass notes balanced with the mid and high notes. There is an additional problem associated with doing this, the amp is no longer feeding the field coil, which is part of the power supply. The amp will be running at higher voltages which will shorten the life of the tubes and components. If a replacement speaker is used that does not have a field coil, a resistor must be used in place. Generally, this will vary between 4000-5600 ohms, depending on the make and model. Check the diagram of the amp for the correct value, or measure the old field coil. The resistor will need to be at least 25 watts, and will have to be mounted where air can circulate around it to cool. Also, remember there are high voltages present on the resistor, and there is a serious shock hazard.