Wurlitzer Cobra Tonearm to Magnetic Conversion

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These are instructions for converting a Cobra equipped Wurlitzer jukebox to use a magnetic cartrtidge in the existing tonearm. An alternate method is to find the tonearm from a stereo model (2300S-????) and use that since it will accept a half inch mount magnetic cartridge without modification.

Materials Needed
Fitting the Pickering EP-DJ/Stanton SM.V3 to the Cobra Tonearm
Check and Adjust the Tonearm
Follow the instructions from the service manual for these items.
Installing the Preamp
I'm not going to tell you exactly where to place the preamp and how to mount it, but I will tell you where not to put it. Do not mount it so that it comes in contact with any of the grounded metal items in the jukebox if the preamp has a metal case. Do not mount it near anything that contains relays or any other coils. That means do not mount it on or near the playrak or the chassis. Once you have found a suitable location for the preamp, run the wire from the tonearm to an input jack on the preamp and then use a good quality RCA cord to connect the output jack for the same channel that you used to connect the tonearm to the input of the amplifier.

Modifying the 532 amplifier.
These instructions may work for the 530 amp too.
Schematic available here. Modified Circuit Diagram
Amp Modification

The Tonearm with the Magnetic Cartridge Installed.
Toneaarm Final

Toneaarm Final

Reducing the Pop Noise When Making a Selection
Here are some strategies that can help if you notice that your getting pop noise from the sound system when you make a selection. There are a number of relays and coils that are energized and then switched off when making a selection. The noise generated when switching these coils on and off can easily be picked up by the preamp.
Tonearm Wire Routing
In my case, I found that the routing of the tonearm wire to the preamp was the most effective in reducing the noise. I recommend experimenting with the routing of the tonearm wire first.

Preamp Grounding
At one point I attached a ground wire from the preamp ground terminal to the record changer. This helped reduce the noise slightly, but was not as effective rerouting the wire from the tone arm to the preamp.

Preamp Location
The location of the preamp can be a factor as well. I mentioned this in the conversion instructions, but you should not locate the preamp near any coils or relays. This means that you should not mount the preamp on the playrak or the chassis. I have mine located on the bottom of the jukebox and approximately 1" (2.5cm) away from the chassis.

Creative Commons License
This work by Carl Haines is licensed under a Creative Commons Attribution 3.0 Unported License.

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