Wurlitzer Side Man

[Jazz P Bass]

This puppy just showed up for a going over.
Going over what?
I don't even know what the heck it is!
(I do now. Thankyou Mr. Google.)
The world's first drum machine.
Any thoughts on what I am getting into.
(i hope the customer doesn't want a midi port)
The first Drum Machine – Wurlitzer Sideman
Synthmuseum.com - Wurlitzer : Sideman

[JHow]

I don't know what your getting into, but it has a cool "Doc Brown - Marty McFly" vibe to it. Post a picture if you find a flux capacitor in there.

[Jazz P Bass]

O/K.
What I found was the motor armature was rusty & the bearings where gummed up.
Got the motor working, the belts & rubber tire are good, checked out the power amp (1-12AX7 & 2- 6BQ5's) That's o/k.
So I end up with a blown side tweeter, Cymbal does not work & above 5 on the volume it gets really hissy.
The tweeters are in series so I wired in a 4 ohm resistor at the blown one.
Gotta track down a 6AV6 tube. I think that is where the hiss is coming from.
I don't have a clue how this thing works.
The preamp is a Huge bundle of wires.
I am going to sleep on why Cymbal does not trigger.

[Enzo]

The hiss MIGHT be not wrong in and of itself.

I've seen a similar but older unit.


Basically, a white noise generator makes constant hiss, then the rotating contacts gate the sound in and out. Buttons select which of the rotary contacts will be live, to create a pattern. A steady on/off/on/off... of white noise results in something that sounds like a high hat. Then a little tone shaping, and the same noise can be gated to sound sorta like a snare drum. SO if the gate is stuck open or real leaky, you get constant hiss/white noise. Now that is from the units I recall, yours make have some other action. or might indeed just be noisy.

Imagine a basic modern drum machine. Now imagine a scalloped disc just above one of the drum buttons. As it rotates, each lobe around th disc pushes the button on its way by, so you get a steady drum beat. Like that.


SO the subassemblies might be a noise generator, filter, gate amp, preamp out , etc.

[Jazz P Bass]

Yeah, same thing.
Big wheel, ganged rotary switch picks which pads to activate.
The pads run on -18Vdc.
Then they are sent to there respective tubes grids.
Here is where I am at.
The motor is good now.
The cymbal did not function.
V-105 6BA4 pentode was bad.
Got that.
At this point everything is functioning.
What I still have is that hiss.
I subbed all of the tubes with known good ones.
Three of lower the 12AX7's are doing it.
V-103 (claves), V-102 (wood block & temple Blk II) & V-101 (tom II & temple blk I)
I tried grounding grids which seemed to help on a couple of them. I may have to change plate resistors on those.
They have a pot adjustment for the cathode resistance.
Every tone except cymbal, brush & maracas.
Why, I do not know.
Maybe I will notate the cathode voltages & Deoxy them & give them a couple of good spins.

[Enzo]

Find somethig working and look at the on and off condition grid voltages, then compare to your noisy stages. A leaky coupling cap could be leaving a gate open a little. Then again it could be just a noisy resistor. SCope it.

[Jazz P Bass]

Wurlitzer SideMan

Thankyou Enzo for the insight.
With that, I checked every "sound".
By removing all of the tubes & reinserting them one at a time I tracked down the hissers.
It turns out that the answer was in those locked down cathode pots.
I deoxied them & when trying to get them back where they were, I stumbled on a gate adjustment.
Set up the hissers for no hiss & that resolved the problem.
Now to find a 2 1/4" paper cone tweeter, 4 ohms, with a horizontal mount of 2 3/8".
(not a current standard mount dim.)
Oh, and by the way, I did not find any "flux capacitors".
What a cool unit.
The first successful commercial drum machine!

[Jazz P Bass]

Here is a repost of the file.

[julianzizko]

Thanks to Jazz P Bass for reposting his notes.

After reading those notes I managed to get the Sideman partially working,
If anyone has a copy of the schematics, or knows where I could buy them I'd be most grateful.
I'd really like to mod this so it can be triggered by trigger pulses from my modular synthesizer, if anyone has any ideas on how to do this please share.

So far I found:

The 12 pole relay was broken, fixed by soldering each of the pairs of wires together.
The tweeter in front of the speaker was blown (I used a 4 ohm resistor to bypass it, I intend to move the identical tweeter under the front panel to the new position.)
Loose wire in the PSU connected to the fuse carrier where the owner has twisted the carrier and snapped the wire connected to it
All of the 12AX7 valves were bad, I tried a known good one in a 5 positions for the drum voices and they started working.
The Maracas, Brush and Cymbal still do not work I suspect the 6AV6, 6C4 and 6BA6 valves I have ordered a complete set of valves and will report back.
The tempo pulse lights do not work.
The monitor plug does not seem to be working.


Observations:

I was excited to find 5k tuning pots for each of the drum voices, I may bring these out the front panel.
The drum synthesis section plugs into the amp with a 1 metre coaxial lead with a phono connector, this can be plugged directly into a DI/Preamp insted for a clean line out, alternately you could connect a Weber Mass do get the sound of the valves in the amp section.

It sounds amazing, with an (expensive) NOS Phillips 12AX7, I hope the replacements I'm buying will sound as good.

What an amazing machine!