Upgrading the sound system on a Wurliter 2150

I've started several threads asking specific questions as I have worked my way through a rebuild of a Wurlitzer 2150. Thanks go to several on this forum, who have helped me through these issues, such as our esteemed moderator, Ron. However, the majority of the credit/blame/inspiration falls on Rob's lap. He planted the seeds. In any case, I thought it would be worthwhile to create a new thread that detailed all of the steps, parts and pieces I used. The specific parts and pieces were based on recommendations from Rob, other posters, various suppliers, and other sources. I'm not suggesting these are the only or best choices and, in fact, would appreciate others chiming in if they have other options worth considering.

It is important to note what my goal was, as this influenced some of my choices. I wanted to largely preserve the inherent sound rendering of a 60 year old, tube amp. This meant no substantive modifications to the amp, leaving me with only the input and output to fiddle with. I was not after digital quality sound. I was striving to make the main limitations be the capabilities of the amp, the quality of the record, room acoustics and my own hearing.

With that goal in mind, I started with the amp.

The Amplifier
You need to know that this jukebox had been actively used by a large number of rodents for a number of years. Besides the usual gunk, all of the internals were covered with rodent crap and tons of pieces of acorns. I have no idea how long it was kept in some garage or storage shed out back, but it had to be a number of years.
Given this, it was safe to say the amp had issues. I immediately sent the amp to Bill Bickers (Jukebox Friday Night). Bill is in GA so he is not that far away and was recommended by several people. He checked and replaced bad tubes, replaced all the capacitors, repaired several traces, etc. Unfortunately, UPS misread "Fragile" as 'Toss onto the back of the truck from a distance of at least 10 feet" and damaged the amp when shipping it back to me. I tried my best to fix the amp by replacing tubes, reflowing solder, etc. before giving up and sending it back to Bill, who was able to find the issue (cracked trace, which he reflowed). Bill graciously fixed the problem and sent it back in about a day. While Bill had the amp, I also had him modify it to handle a ceramic cartridge. As I understand it, this entails 'breaking' a couple of traces to bypass part of the amp. I believe it is something that I could have easily done; however, since Bill had it and was happy to go ahead and do it as part of the rebuild, it was a no-brainer to have him take care of it. That was it for the amp. Basically, just bringing her back up to 'as new' state.

Cartridge, ceramic (and tonearm)
Just like the amp, I assumed the cartridge would need replacing. In talking to a number of people, I kept hearing the same thing. 'Cobra's are very expensive and very inconsistent' I had one person tell me they bought a batch of them once and while a number were just plain bad, what was more surprising was the difference in sound quality between them. Some boomy, some tinny, some muddy, some loud, etc. I was told that a ceramic cartridge was better quality and less expensive than the Cobra's. The problem is that the 2150 tonearm cannot readily accept the standard 1/2" mount used by many ceramic and magnetic cartridges. Beginning with the model 2300 (I think) Wurlitzer started producing a tonearm that had the two screw holes to support the 1/2" mount cartridge. So, I bought a kit on e-Bay containing a tonearm from a 2300, weight and ceramic cartridge. There is no discernible difference between the original tonearm other than the two holes. Now, the other issue you have is that the 2150 is a mono jukebox, while the cartridge is stereo. So it was necessary to splice together the right and left channels into a single wire and the left and right ground into a single wire. These were, then connected to an RCA plug. The final difference between the Cobra and the ceramic cartridge is that the Cobra is heavier. While there is an adjustable counterweight built into the tonearm, it cannot compensate for the weight difference between the two cartridges. So, you need to place the counterweight in the middle and then add weight towards the front. As noted, the kit I bought included a weight with sticky tape on it but you could use a fishing weight, washer or a wheel weight (for a motorcycle wheel). I used the method outlined in the manual to balance it. After installing the tonearm, some additional adjustment, via the counterweight will be required.

What I discovered was that the sound was fine. However, after about 6 weeks the sound started getting very erratic. It would change in the middle of a record. Sometimes it would get muddy or gain/lose volume. I thought it was related to stylus pressure, but it was very inconsistent. In talking to multiple people, the consensus was that the the cartridge was starting to fail and needed to be replaced. Here is where a seed planted by Rob took hold. He had mentioned using a magnetic cartridge with preamp. Now seemed like the time to take that plunge.

The main 'issue' with moving to a magnetic cartridge is the low output level of magnetic vs ceramic. So low, in fact, that it requires the addition of a preamp. The good news is that there are lots of preamps available since most newer receivers don't have a phono input. If you want to add a turntable, you need a preamp. The other good news is that suitable preamps are inexpensive (under $50). That having been said, several people I asked felt the quality on some of the new stuff was lacking. So, when Rob suggested going with an old Realistic 42-2109, I started researching that option. There seems to be a good number of people out there that swear by this little guy. Plus the original purpose of the 2109, as stated in the marketing materials, was to address upgrading from a ceramic to magnetic cartridge, so I was confident that it would fit my needs. They are also readily available on e-bay. I ended up finding a NOS model 42-2101. The only difference I could see is that the 2101 is made in Japan (as opposed to Korea for the 2109)

Next up was a magnetic cartridge. The Stanton cartridge that was recommended was nowhere to be found. I couldn't even find a used one. I wanted something with a fairly high tracking weight. I also wanted a spherical stylus as my research indicated that while an elliptical stylus was great for LPs, it was not recommended for 45's. I found a new Stanton 500 AL II DJ cartridge DJ PRO with the D5100 ALII diamond stylus, which tracks between 3-5 grams. It was on e-bay for $30. (The seller had three and they all sold within a few days so I'm guessing it's popular with DJs)

Hook up was easy. The magnetic cartridge was an easy swap. Plugged the cartridge line out into the preamp and went from the preamp to the phono turned it on and got a ton of hum. On the 2150, the cartridge plugs into a jack at the back of the record player unit, then another cord runs to the amp (or preamp in my case). The jack is riveted to the back of the player. When I bypassed the jack, it sounded fine. Touched base with Rob who confirmed that the riveted jack causes a ground loop. The solution for me was to simply buy a cord from the local Radio Shack that had a male jack on one end and female on the other so that I could make the run from the cartridge directly to the preamp.

Now, one side benefit of this setup is that since the left and right channels are merged at the cartridge, only one side of the preamp is used. And since the preamp has mirrored circuits for right and left, if something were to happen to the preamp, I would be able to simply switch to the other channel.

All that was left is the speakers, which in my case meant simply adding some help to the high end