How to Convert a Wurlitzer 206 into a Wurlitzer 200
The Wurlitzer 206 is the student version of the Wurlitzer 200. It is equivalent to the 200 in every way, but it is mounted on a cabinet instead of legs and some features of the amplifier are disabled. However, all of the components that are in a 200 are also present on the circuit board of the 206. Enabling vibrato and the aux output is therefore as simple as adding some wires and a 10k potentiometer. Here is how we do it.
Modifying this Wurlitzer requires some prior experience with electronics that is outside the scope of this article. All Wurlitzers have high voltages that can persist even after the amp is turned off and unplugged. Attempting to modify your Wurlitzer without following the appropriate safety protocol could lead to damage to the Wurlitzer and/or injury to yourself.
Note that this is a guide for the Wurlitzer 206, not the 206a. Modifying the 206a requires a number of additional steps because the vibrato and aux components are not already present on its circuit board and instead must be added.
Adding Vibrato to a Wurlitzer 206
First, we remove all of the student-related wiring and the large self/ensemble switch which controls the output of the keyboard. None of this wiring is remotely useful because, in order to function properly, it requires multiple keyboards connected in classroom configuration. We also remove the wiring associated with the jack that is mounted to the left side of the keyboard. We will reuse this jack as the aux output. Finally, we remove the jumper wire between points 12 and 1 on the circuit board. This wire is grounding the vibrato circuit, and we need these points clear in order to mount the vibrato pot wiring.
Next, we mount a 10k linear potentiometer where the self/ensemble switch used to be. The wiper connects to point 12 on the circuit board, while the input lug connects to point 13. The third lug is grounded. We now have vibrato.
If you are ready to convert your 206 to 200 specs, check out our Wurlitzer 206 Vibrato & Aux kit that supplies all of the parts you will need to do so. If you have a 206A be sure to select the correct corresponding kit.
Adding an Aux Output to a Wurlitzer 206
This is the Wurlitzer 200 circuit board before any restoration. The three empty metal pegs in the front-center are where the aux output circuitry mounts.
The aux output on the 200 is very minimalist, and basically just sends an attenuated portion of the preamp signal to a jack. The attenuation is necessary in order to reduce noise. Previous versions of the schematic used larger resistor values for less attenuation, but because users complained that it was noisy, Wurlitzer started reducing the resistor values for the final releases of the 200. (They also developed a more powerful aux out for the 200a, but that doesn’t exactly help us here. Anyway, the 200 aux is extremely usable as-is, and sounds even better when you plug it into a preamp.)
The first step is tying our two resistors to the appropriate points on the circuit board. We mount a 6.8k resistor between points 6 and 7, and a 2.2k resistor between points 7 and 1. We then use a short piece of wire to connect point 6 with point 5, where the volume pot wiper connects to the board. The jack itself connects to point 7 and 1 with two long pieces of twisted wire.
Troubleshooting
Now, the keyboard should have both vibrato and aux output capability. We actually just wired four amps this way, and they all worked. Pretty impressive for components that have been dormant for over 40 years. But, if we didn’t, here’s how we’d troubleshoot it:
The orange capacitors are the tremolo capacitors in a Wurlitzer 200. They provide the phase shift that allows the circuit to oscillate.
Troubleshooting 206 Vibrato
Confirm that the potentiometer is connected to the correct points on the circuit board.
Confirm that the pot is indeed a 10k linear pot. This may require removing it from the circuit and testing it with a multimeter.
If you’re positive that the pot is correct and everything else is connected correctly, there may be a bad component in the circuit board. Problems fall into three main categories: a fault in the power supply, a failed or drifted component in the vibrato circuit, or a failed or drifted component that is preventing the vibrato signal from reaching the preamp.
A fault in the power supply could prevent the vibrato transistor from receiving adequate power. If the transistor doesn’t operate with enough gain, the circuit won’t oscillate and the vibrato won’t work.
The vibrato transistor itself may be faulty and should be replaced.
One or more capacitors in the vibrato circuit have failed. These capacitors have relatively tight tolerances: 10%, where most components in the amp have a 20% tolerance. This is because, if one of these capacitors drifts far enough, the circuit might not achieve enough phase inversion to oscillate.
One of the components connecting the vibrato circuit to the main preamp circuit has failed and needs to be replaced.
Troubleshooting 206 Aux Output
Confirm that the 1/4” cable that you have plugged into the aux output jack is working.
Confirm that the aux jack is wired correctly and connects to the correct points on a circuit board. This is particularly important if you have replaced the original jack with a more complex one.
Confirm that the aux jack is working, either by plugging in a cable and testing its continuity or replacing it with a known good jack.
Further Reading
Browse all of our articles on restoring vintage gear. Or, click on an image below.
