From the Archives: Wurlitzer 726
We had this Wurlitzer 726 for about two minutes before someone snatched it up, so we don’t have very many photos of it. But we remember it fondly because it was definitely one of the best-sounding Wurlitzers we’ve ever played. It is rare that a 726 amplifier (i.e., 140b amp) is in excellent working condition, but when it is, the tone is very sweet.
The 726 is the student version of the Wurlitzer 720b, itself the console version of the 140b. It is exactly the same as the 140b in all respects, except for some minor modifications intended to make it more useful in the classroom:
The vibrato circuit is present, but disabled.
It has “umbilical cord” wiring and a pair of ports at the back. The keyboards in the classroom connected to each other via these ports.
The cheek block contains a self/ensemble switch, which is associated with its classroom functionality, as well as a speaker/headphone switch that toggles between the onboard speaker and the built-in headphones.
This 726 was originally from a college, and would have been part of a classroom set of several other 726 models. The teacher would have used the same keyboard as the students, but with a control unit that would allow him or her to listen to various students’ pianos, and offer instructions.
This particular Wurlitzer was in great condition. The amplifier worked well, but it had a little bit of noise that we ultimately remedied by redoing part of the wiring harness. We also enabled the vibrato.
It is always a pleasure to hear a functional 140b amplifier. The germanium power transistors give it a unique warm tone, but the circuit is fragile and prone to malfunction due to aging and stress. Many 140b amplifiers arrive to us broken (case in point: we have a 720b in the queue with a broken amp).
How to convert a Wurlitzer 726 to 720b specs
Enabling the vibrato in a Wurlitzer 726 (or 146). This is theoretically very simple, but unfortunately requires an obsolete part (which of course it does).
Just about everything that the vibrato requires is already in the amplifier. The only thing missing is the vibrato control, which in the 720b is mounted in the cheek block and connected to the amp via the wiring harness. The vibrato control is a 100k linear potentiometer. If you have an original vibrato knob, you will need a half-shaft style pot. If you are using a different knob, you can use any 100k linear pot.
The wiring harness is where the obsolete part comes into play. Ideally, you can connect the vibrato pot to the amplifier by adding two pins to the wiring harness plug on the amplifier chassis. Unfortunately, the molex connector (and its corresponding pins) are not manufactured anymore. You may be able to repurpose the self/ensemble wiring for its pins. Unfortunately, we don’t have a 726 to confirm what the best method is, but if you are enabling vibrato in your 726 feel free to contact us via the Wurly Hotline and we can help you out.
We honestly worked on this keyboard so long ago that we don’t remember how we connected the vibrato to the wiring harness in this instance. For subsequent student-model 140b-style Wurlitzers, we were actually fortunate enough to have original 140b wiring harnesses on hand, so we haven’t dealt with this issue in a while. We just unplugged the original harness and plugged in the vibrato-enabled 140b wiring harness. So, if you can find a non-student 140b amp that someone is selling for parts, it will have the same wiring harness and you can use it in your 726.
Replacing the headphone switch with a headphone jack. The original headphones are attached to the keyboard, probably because Wurlitzer didn’t trust that students wouldn’t lose them. The cheek block has a switch that allows the user to toggle between the headphones and the onboard speaker. If you want to use your own headphones, you can remove the switch and install a switching jack instead. This type of jack cuts the speakers when headphones are inserted.
Removing the umbilical cord wiring. A 726 has two ports in the back, which were originally used to connect the student keyboards to each other. If it still has the original wiring, each port will have mains voltage (i.e., 120v wall voltage) on it. This can be a shock hazard if you put your fingers in an open plug while the keyboard is plugged in, even if it is not switched on.
One of your student ports may currently be occupied by a power plug. If so, you can leave it as-is: you are clearly using that mains voltage wiring, and if the port is occupied by a plug nobody can stick their fingers in it. However, this leaves one open port that you are probably not using. (Unless you are using it, because you have a full classroom’s worth of 726 Wurlitzers? If so, carry on.) In this case, you should cut all wiring from the unused port.
Because the 726 uses the exact same amplifier as the 140b, you will also have the male end of a power plug on the chassis itself. In our 726, the student port provided wall power by plugging straight into the plug on the amplifier. This makes the student port a totally unnecessary middleman that runs 120v all over the inside of the cabinet for no reason.
In fact, the best way to handle the power wiring in the 726 is to:
Replace the power plug on the chassis with a three-prong IEC socket
Use a regular IEC-style power cord and plug it straight into the amp chassis
Remove all student wiring that runs to both ports
You can leave the ports themselves for the aesthetic — and it’s actually better if you do, because if you remove them you’ll be left with holes in the back that will just let dust into the cabinet. As long as you cut all wires leading up to the ports, they will be safe. Obviously, do this while the amplifier is turned off and unplugged.
Further Reading
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