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Amp Repair

Amp Tubes





The two most important things about jukebox restoration are looks and sound. A "Grade 1" appearance restoration will come up short if it doesn't sound as good as it looks. Sound system repair is no place to cut corners. Re-coning of speakers if necessary is a good investment, older speakers can rattle or sound mushy if the cones have deteriorated. This generally shows up more in heavy bass notes.


Bad or incorrect tubes are another source of distortion. It is a complete and total waste of time to plug new tubes into an old amp that hasn't been repaired. New tubes can be ruined in a matter of minutes if circuit or transformer trouble is present.


Decent tubes are beginning to get scarce. Distributors are relabeling lower priced and unsalable tubes with higher priced numbers and the average person doesn't know the difference until the problems they are having get worse with a change of tubes.


I get several calls a year from collectors who settle on one model of jukebox and end up with two or more of them. The calls usually go something Re this: "Bill, I have three Seeburg 222 jukes and they all sound different. How can I get them to sound exactly alike?"


The short answer is: you can't! Why, you ask? It is next to impossible to get 2 amps to sound exactly alike. Manufacturing tolerances alone will cause sound variations. Add 30 or 40 years to the mix, and the fact that three different people may have worked on the amps, and you begin to see the problem.


Different brands of tubes, even though they are the same number, will not sound the same. The brand, quality and construction of capacitors will cause variations in sound. But the biggest difference is the output transformer. The transformers were wound on lathes by human beings. All it takes to cause one to sound differently is a few more or less windings the specs called for. Also, if the person overlaps a few turns, lets the metal core touch windings, etc. there will be a significant change in sound.


I personally can't remember hearing two amps that sounded exactly alike. However, I have found that for pure power, bass response, and clarity of music reproduction, the Seeburg R is the king of the hill, followed closely behind by the V and VLs.


I suspect that a lot of this has to do with the placement of speakers and the size of the cabinet. Some jukes have great amps, but the arrangement and type of speakers kills any chance they have of really knocking your head off with sound.


Most, if not all, AMI jukes have one or two bass speakers either down low in front, or in the middle of the grill. The bass speaker is tied to both channels, which means that there is no stereo signal available. The two side speakers are the only source of separation of the sound. They do sound great because twice the power is being applied to the bass signal, but very little is left for the side speakers, hence there is really not much stereo effect. You have to stand directly in front of the juke to tell that it's stereo.


Early Rockola stereo jukes really weren't because both channels were fed into one 12" speaker. To get stereo, you have to ran remote speakers off the terminal strip on the amp. Most people don't have the remote speakers, or even enough room to mount them.


Early Wurlitzer stereo jukes had two different channels, but one 12" speaker was really a midrange, and the other was for bass. Yes, there was separation of the channels, but each was intended to respond to a different frequency response. If you sit directly in front, down low, you can hear this.


Seeburg's early stereo jukes were true stereo. But the down side was that their first amps were unbelievably complicated! They took the "British" route and over-engineered the system. They can really be tough to get right, however when they are, they sound great.


All early jukebox stereo amps were slightly down on power. Most mono amps were rated at 25 watts, but could easily put out 55 watts when pushed. The early stereo amps used 6973 tubes in the output, and the best you can possibly hope for on a good day is about 15 watts per channel. Okay, they were rated higher, but the power just wasn't there. So, the result is that an earlier mono amp will outpace the stereo amps by a mile.


And the problem got worse when they switched over to solid-state amps. Almost everyone was using germanium transistors in the output stages, and they just didn't get the job done. They were rated at 25 watts per channel, but 10 is closer to the truth. AMI amps used early versions of silicon transistors, which helped, but the power still wasn't there. After all, solid state technology was fairly new at the time.


Add 30 years to this mix, and you begin to understand why some of the mid-60s boxes sound so bad. Manufacturers didn't stand still too long, and soon amp design did catch up. By the late 60s, Seeburg and AMI were out front in sound. It took another few years for Wurlitzer and Rockola to catch up. Actually, Wurlitzer didn't redesign their amps until two years before they shut down. I suspect that they just didn't have the funds for major changes. They had been losing money for years, and the company was drained.


Should you avoid buying an early stereo juke? Probably not, since many of the advances in components can be retrofitted into the early amps, which will make a noticeable difference in sound quality. Also, these same boxes are still real bargains today. In a couple of years this may not be the case. This is a very good time to look to the future and buy another box even if you don't need it today. If nothing else, it will be good trading material in the future.

From James Loflin of Music and Games Service comes a tech tip: "One way to get fairly decent sound from a Wurlitzer using a cobra cartridge is to use a 2 mil needle on 45 records.  The needle will ride higher in the groove and eliminate the distortion normally associated with playing a modern stereo record on an early system. The bass will be noticeably stronger, and the midrange clearer."


If anyone else has a tech tip or just a bit of advice that they would like to share with the readers, please send it to me by e-mail or letter and I'll be glad to share it in the upcoming months. Also, any questions that arise will be answered in upcoming columns.