Wurlitzer 2304S Repair Log and Cries for Help Along the Way

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I am a brand new jukebox owner and have experience with electronics, but never a jukebox! Most definitely never worked on something this old! I have an odd combinations of components and would like to reach out and ask for some help. I identified my amplifier as a Wurlitzer 538 Amplifier. The label was mostly rubbed off but I do know the 538 is very close to the 534... I am pretty sure this is a 538 as the can caps match the values they should be in the 538, and the can caps in the 534 are different values.

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So I purchased the cap kit for the 538 and completed the capacitor rebuild. This was my first time ever replacing can caps so here is how it looked when I was done, notes on how to do it better always appreciated.

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Hurray! I then turned my attention to the power supply. This is when stuff gets weird... it seems my power supply is not for a 538, at least, it definitely is not the same power supply that is in the full 538 amplifier schematic. So I begun searching and this is 100% the power supply in the 534 schematic! It has the same single tube on the chassis and it has the full bridge selenium rectifier. Well I though okay, I do have a full bridge replacement for this rectifier so I will replace that. So I did. What I do not have, is the correct capacitors to replace the can caps in this power supply, since Victory Glass sent me capacitors for the 538 power supply. So I ordered the few caps I need and am waiting for those to arrive to complete the recap of this entire unit. But I figured I would give the unit a chance to turn on and see how it does. At first, after some squinting and flinching for a first time power up, I turned it on and everything seemed okay. But my 30V line out of my full bridge was missing, so the motor did not spin and it seemed there was an issue. Then, randomly, about 5 minutes later, my 30 volts appeared, my 5U4 lit up and the jukebox came to life! I was able to put money in and see the wheel attempt to select a record! Then again, just about as fast as it came, it left again. No more 30v line, no more glowing 5U4. Dead other than the nice glow of the florescent bulbs.

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Okay, so I started looking into the power supply to see what has been done, first, I noticed 3A fuses had been installed in the 2A fuse holders. When I got the jukebox, these were both blown. I made a rookie mistake and assumed the previous owner had put the correct amp fuses in and just replaced them with 3A fuses. After I noticed my mistake I have put 2A fuses in. I am REALLY hoping I did not cause damage to the transformers by doing this but I guess if the previous owner blew 3a fuses... the damage was probably already done. Anyways now I am sure my full bridge was wired wrong, as the schematic shows -30V going to the output of the junction box and mine was outputting +30V. I think I did have it backwards and send +30v to the junction box. Yikes on my part. Anyways waiting for my capacitors to replace the can cap in this power supply, as well as a new 5U4 tube for good measure. I am unsure what I fried when I put the wrong polarity in the 30v line but it seems to be completely dead now. Also what would cause my 5U4 tube to not work until it randomly lit up with the 30v line? I figured the bad cap could cause this but after looking at the circuit I am unsure the capacitor would effect the 30v line. Thanks everyone.Screenshot 2025-10-02 100636.png


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UPDATE:

I have found that my issue was not the power supply at all. See attached photo. The MAINS power goes through a jumper in the "Junction Box" This box is the connection to the upper record selector unit. Once I moved one of the selector arms, their was no longer an open circuit between the pin 8 to pin 3 JUNCTION BOX. I am not sure what is causing the open circuit, but this issue is definitely inside of the record selector part of the jukebox. something is cutting off main voltage when it shouldn't be. I have been unable to find a good schematic or explanation on how the record selector works or where the main voltage flows through it. If anyone has references please let me know. I also made a little video to better describe the issue.

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If you haven't already done so, do yourself a favor and get an original service manual, or at least a quality reprint. Wurlitzer manuals from this era typically have a section showing the sequence of operation in detail, with isolated schematics to help you understand how it's supposed to work.... as well as fold out pages with the entire wiring diagram.

Trying to figure this out from scans found online is a recipe for madness, IMO.
 
The bridge rectifier replaced the original selenium (toxic) rectifier which was installed (which looks like stacked plates in the diagram).

The biggest problems with old juke boxes are:
1. The grease in the mechanisms has lost all it's oil, which leaves wax or clay. It must be cleaned out, refreshed with Lithium based grease, and then moved through the cycles to lube everything up.
2. The contacts are typically fogged over with corrosion. You need to use a flex file to clean up the contacts.
3. The Jones Plugs (large blocks with pins and a tab) are typically corroded. The contacts are tin, which corrodes resistive. You have to clean them up with a Dremel tool or equivalent and then treat them across all mating surfaces (once you get them bright and shiny) with DeOxit.
 
As far as good schematics, look on your favorite search engine. People sell repro manuals.

If you can find an original manual, it may cost more, but it's an ORDER of magnitude clearer.

Like this ad for a Repro manual.

 
Thanks @ArcadeTechGW! Appreciate it. I did get it working. Looks like my latest issue was the safety switch which seems to trigger if the head of the plastic record holder turns. I have ordered a repo manual. Will wait for it to get here. In the meantime I have this jukebox that plays but sounds like crap! Was wondering if someone could point me in the direction to start for identifying the noise. Speakers? Record needle? Amplifier? Probably a combination. Thanks again.

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First, get your expectations under control for sound quality. Wurlitzer made some beautiful jukeboxes, but to my ears, they had the worst sound quality of any of the classic jukeboxes. They stuck with a ceramic phono cartridge long after the other companies went to magnetic... so you won't get much high end. That said, your machine should produce decent bass and midrange, if everything is working right.

I believe you should be able to input a line level source... CD player, phone, laptop, whatever... thus isolating the needle/cartridge/tonearm from the equation. The speakers from this era are quite robust, and usually are not a problem... but anything is possible. You could wire up externals for testing.
 
Also... I don't think you mentioned the tubes. A tube tester is handy for ruling those out. It's very possible you have one or more tubes dragging your sound quality down.

Of course a worn needle and/or worn records can cause bad sound quality... as well as mechanical issues with the tonearm.

Aren't jukeboxes great?
 
That muddy sound could be:
1. Bad tubes. Do you know of someone with a tube tester close to you? I have one, but the gas to get there would be expensive.
2. Bad electrolytic capacitors, including the large multi-element ones. You may be able to get replacements at John's Jukes, or Hayseed Hamfest. You'll need a bigger soldering iron to get those out.
3. Bad needle / cartridge. The needle in the cartridge is suspended between some rubber mounts, which typically rot away.
 
@RusselMania @ArcadeTechGW thanks again. I do have a tube tester, it is a B&K model 650. I had to replace some capacitors in it as well. But it does not have the ability to test all my tubes some it needs an expansion module I don't have. All the tests seem to work in it besides test 1. (Sucks when your test equipment has things you need to test ;)) Thanks for the idea for trying a different input. I will try that and see if the sound quality is still bad. I have replaced all the capacitors besides the can cap in the power supply in the jukebox, which I will do soon. I bought a cap kit from victory glass. I will see if I can get my tube tester fully working or ask around to borrow one.
 
@RusselMania @ArcadeTechGW thanks again. I do have a tube tester, it is a B&K model 650. I had to replace some capacitors in it as well. But it does not have the ability to test all my tubes some it needs an expansion module I don't have. All the tests seem to work in it besides test 1. (Sucks when your test equipment has things you need to test ;)) Thanks for the idea for trying a different input. I will try that and see if the sound quality is still bad. I have replaced all the capacitors besides the can cap in the power supply in the jukebox, which I will do soon. I bought a cap kit from victory glass. I will see if I can get my tube tester fully working or ask around to borrow one.
That would be your best bet.

Did you look for a later table for your 560? B&K put out some revisions.
 
I have not gone through the tubes yet but wanted to post an update to the current situation since I spent some more time troubleshooting. I was able to hookup a CD player to the input of the amp and it sounds just as bad. So, needle does not seem to be an issue, we at least it is not the main issue. Next, I think my 6973s are red plating. I have attached a photo. I have went through and probed all of their inputs and they are all within what the schematic says... 380v on pin 9 read as 388, 20v on pin 7 read 20.8v, 290 on pin 8 read 300. I have now replaced every single capacitor in this system. I checked resistors around the bias lines on the 6973 tubes and they all test fine. I am starting to just think I have bad tubes. Not much else could be wrong... which sucks since the 6973s are not cheap. Audio still sounds like a gargled mess. I have swapped a few of the 12au/12ax tubes as i had a few spare laying around but that has not helped.
 

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Bad power tubes would not surprise me. 6973's are known to be less hardy than "normal" power tubes (such as a 6L6). They were an attempt to make a tube that did the same work as the older ones in the same package. I don't know all of the reasoning for their creation, but they date from an era when solid-state technology (meaning transistors) was spreading rapidly, and miniaturization was the goal throughout electronics. I think smaller tubes like the the 6973 were an attempt to keep tube technology competitive in this context.

Unfortunately this means they were only used in new gear for a couple of years, before transistors took over altogether. And the few niche markets that stuck with tubes -- mainly guitar amps and audiophile hi-fi -- stuck with the larger, beefier tubes like the 6L6.

The good news is, if you've done your rebuild well, and you get a good set of 6973s, they should hold up fairly well and sound fine. I've got at least one juke (a Rockola) that's been doing well with 6973's for a decade or so at this point (knock wood).

I haven't priced 6973's in a while... I'm almost afraid to. Seems like there was a Russian remake of them at some point... Electro Harmonix, maybe? Those might be okay if you can find them.
 
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And yeah... it's hard to tell from pics, and tubes can sometimes do some weird visual stuff and still be okay... but what's going on in your pics does look kinda unhealthy.

You might reach out to Bill Bickers (Jukebox Friday Night)... he will sell you good tubes for as fair a price as you're going to find. And he knows these amps inside and out.
 
@RusselMania thanks again, yes I did some more testing and on the bias side of the tube i see 0V sometimes even positive voltage. The schematic has no voltage rating for this side of the tube but I believed it was supposed to be -30v. I gave the expert at Jukebox Friday Night a call, he set me straight on a few things. First thing he told me was this amp is a cathode bias circuit, not a fixed bias circuit. So I should see near 0v on the control grid line. This is good to know. On startup I do see some wild voltages but this is with a digital meter. This is the second thing he told me, only use an analog meter on these analog circuits. He told me to check my plate voltages on Pin 9 of my 6973s and make sure all 4 tubes have very close to the same value, this is crucial. I will do this tonight or later this week. Also he told me to measure the resistance between the primary winding and my windings to the 6973, that is found on pin 9. This should be the same for both sets of 6973s. This is also crucial. I ordered a tube kit from him and assuming all of these things test good I should be good to go. New tubes should get this thing up and running and sounding better. He is suspect of a bad transformer leading to my issue of red plating. After this extensive testing, the issues can only be a few things:

1. Bad coupling cap (but all caps have been replaced, still needs tested)
2. Bad Transformer
3. Shorts in the tubes or bad tubes

I am hoping that it is just bad tubes, as he said, putting all new capacitors in will bring those tubes up to voltages they most likely have not seen in a very long time. This could have killed them. I am also waiting on a new 83 rectifier tube for my tube tester. Once I have that I should be able to fully test all of my tubes, I will not be putting any new tubes in till I confirm this issue lies with the tubes. This repair has already been expensive enough! And it might still need a new transformer! Thanks again all.

P.S. he also told me in all his 50+ years of working on jukeboxes he has only had 2 bad selenium rectifiers. He told me to just put the selenium one back in, or at the very least, add a voltage drop resistor to make the output what the motor expects (around 28v, even though the schematic calls for 30). He said overpowering the motor will lead to the record selection system slamming the pins down for the record selection or overshooting the record selection.
 
Bill is the man. He has been working on these amps since before I was born... and I am not exactly young!

I would think a bad transformer is pretty unlikely... fingers crossed for you.
 
After a long troubleshooting I found I was missing ground in my volume control circuit. Now, both channels sound pretty good! One channel is still noticeably quieter than the other but at least it is a fully working Jukebox. I ended up doing a full recap, new tubes, and it desperately needs a new needle as well.
 
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