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Wurlitzer 1600 mag cart mod help


LovelyCoCoNutes

Question

I am workijg on restoring a wurlitzer 1600 juke with the 518 wurlitzer mono tube amp.

 

I recapped the amp, but the needles are shot.. And for the price of the needles and shipping... I can get magnetic carts and a phono preamp to mod to the amp.

 

I have seen this done for other amps, the 536 i believe, but I am not sure how to mod the 518.

 

 

Is anyone familiar with this?

 

I have the service manual with schematics of the 526 and 518 amp.

 

 

Any help?

 

Also the juke plays, and I can hear the song, but the needles are shot. Zenith cobra green.

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So I read an article by a guy named Carl Haines http://www.carlhaines.com/jukebox/cobra.htm

 

About modding the wurlitzer 532 amplifier to accept the phono input.

 

Here is that circuit

ampMod.md.png

 

 

Now it seems he is jumping the volume control tube valve and putting the signal after the caps he pulled.

 

What I do not understand is the why. Are the caps acting as filters? The cobra needle apparatus seems to be refered to a frequency generator.

 

I do not understand the circuit, and I have not seen anything explaining it yet.

 

 

Here is the 518 amplifier partial schematic:

 

Screenshot_2017-06-24-07-17-26.md.png

 

 

Similar but different....

 

 

This is where I am at...

 

 

For postarity here is the rest of the instructions for modifying the 532 amp. Again Carl Haines.

 

"Modifying the 532 amplifier.

These instructions may work for the 530 amp too.

Schematic available here.

Remove C6

Remove C7 Just cutting the leads is sufficient to remove the components. If you leave enough of the leads from C6 behind, that will provide you with a place to attach the potentiometer later. Check the PCB layout for the location of C6 and C7.

Add the 250k ohm potentiometer to the ground side of C7. Use one of the non-wiper connections of the pot to make the connection. You will want to mount the potentiometer to the top of the PCB. Mounting it to the top will allow you to adjust the potentiometer while the amp is installed in the jukebox and will reduce the risk of you lifting or damaging a trace on the solder side of the PCB.

Connect the wiper of the 250k ohm potentiometer to the junction of C6, C7, R4, R5 (the other side of C7 should work).

Move the wire for the center conductor of the input RCA jack from its current location to the unconnected non-wiper connection on the potentiometer.

Set the potentiometer to pad the output of the preamp so that it falls within a reasonable range for the ALC circuit. Measure the ALC control voltage and adjust the potentiometer so that when you play your loudest record the voltage is no more than the voltage when the amplifier is on but muted. On the 532 amp, you can measure the voltage at pin 4 of the muting plug. This is a high impedance circuit and the meter will have an effect on the voltage. Take a measurement for only a moment at a time. How long depends on how quickly you meter can give a reading. After I adjusted the pot, it was set for about 200k ohms padding. Your results may vary."

 

 

 

 

Any help is appreciated, I am working and have not been able to really attack this problem.

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Hi,

I have a Wurly 1700 and thought about making the same changes as you are considering.

 

After making inquires to providers in the US, I decided to live with the Cobra system. I thought that the changes were a little too difficult with my limited electronics experience.

 

Just to add another issue, some of the repro Cobra needles are not too good (very expensive also).

I have bought 2 that provided poor sound.

 

 

Good luck, I will watch your progress with interest.

 

Gordo....

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