hardware details

The tone generator modules contain dozens of of more or less rotten "explosive candy" paper capacitors those reliability is very questionable. As a safety measure I already replaced the ones in the power amplifier, because the previous owner said that the amp crackled and smoked a bit when he plugged in the HV connector of the organ during operation, and because the EL12 power tubes are expensive to replace and a short in the wooden cabinet could cause a fire. But to replace all of them in the organ would be a tremendous lot of work. Unfortunately I not even have schematics to determine the proper cap values for a replacement; the writing on the cracked and dirty capacitors is partly badly readable. But I bought already new capacitors and will repair this thing when I find time in future. This strange thing is like a piece of ENIAC, and feels like repairing the tube operated time machine in the movie "The Time Travelers" from 1964.

The amp's serial number plate.

Now take a look what's inside...

Here you see the large loudspeaker and the 2 big EL12 power tubes on the chassis.

When on, you can see the tubes glow and the bright red shine of the pilot lamp.

Although this mains transformer block may look small and harmless, I estimate that its solid, heavy iron core incorporates at least 65% of the weight of the entire amplifier.  Above it you see the 2 EZ81 rectifier tubes; in one of the EZ81 and one EL12 tube there is weak blue ionization visible, possible a remain from a previously broken grid capacitor.

The instrument can play loud enough to annoy neighbours tonight, but I don't think that it is louder than the amp of average 1x EL84 tube radios, despite the 2x EL12 tubes look like something as big as KT88 and by their appearance I would expect rather 30W power than just 5W. It may be that the ionization in one tube eats up the power, or that just the huge loudspeaker has lost most of its magnetism (which is rumoured to happen with that old speakers), or that a small defect in the organ makes it quieter. (Its internal preset volume trimmer is all way cranked up.)

The organ connector has this pinout: (counting left to right anticlockwise)

"-" 37.8V AC "-" 6.3V AC +300V DC audio in GND "+" 6.3V AC "+" 37.8V AC

The organ tube heaters are wired in series and supplied by the 37.8V AC output (likely to reduce the needed current on the supply cable); the 6.3V output is not used.

Through the knee lever hole it was extremely easy to touch the highvoltage electronics of one of the tone generators; I am not sure if there ever was a protection against this (e.g. in form of a latex rubber bellows that disintegrated over time by oil/ bad treatment, or a brittle bakelite board that broke and thus was thrown away) or if in 1950th they really never cared about children safety. I covered it with transparent sheet plastic to prevent electric shocks. (At the left corner is the hole of the power supply/ amplifier cable.)

There is a mystery pair of jacks and the left side. The black knob controls pitch in a very limited range. At the right side is a similar knob for the preset volume control (in opposite to the knee lever volume).

This is the back of the organ with cover cage removed.

There are 12 oscillator modules; each produces one tone of the octave and contains 3 tubes for the 3 octaves of the instrument (top is the lowest).

To tune the organ, this row of trimmers can be adjusted with a screw driver.  As it came, the tone scale sounded quite detuned (especially the "h"); I am not sure if this is due to broken capacitors (the main oscillators seem to use less prone plastic ones) or if this Tuttivox was intentionally tuned like an ancient church organ. (I read that also Arp Schnittger pipe organs etc. often used much different tunings than the modern well tempered scale.) The POKEY composition "One Man and his Droid" (available on the SAP Atari XL music archive) can be played almost perfectly with this scale, but most normal music sounds a bit strange.

To the right is the pre- amplifier and vibrato unit of the organ. At its right side are 2 trimmer potentiometers; the upper one limits the maximum volume of the organ. (Mine came fully cranked up, but I guess that is was originally built in to prevent kids from playing too loud.)

Here you see the custom made special potentiometer of the knee lever. As expected, the uncovered, dirt prone wiper contact causes some crackling noise when moved.

When we remove the front cover, we can take a look at the heart of the instrument...

It must have been a horrible lot of work to solder all these components together. I have no clue how expensive this small instrument was, but I could well imagine that it costed as much as a grand piano. Unfortunately the fully electronic tone generators contain several dozens of "explosive candy" capacitors, and most of them already have more or less cracks in them. Unlike the solid construction of my Tektronix tube oscilloscopes, the 3 dimensional structure of this hardware is rather awkward to maintain, because it consists mainly of brittle, traceless Pertinax circuit boards those are faithlessly bolted and soldered together without removable connectors. Also the selection of components looks rather like a collection of post- war shelf mess than produced by a single factory.

Beside the 2 trimmer potentiometers mentioned above, there are 3 further, black trimmer pots simply hanging on their bare, flimsy wires among components at a circuit board. It must be a more than unpleasant and challenging task to adjust these during operation, because the smallest mistake can cause things to bend, short and burn out, or makes you slip with your (hopefully gloved) hand or screwdriver into the high voltage electronics.

Every tone generator module contains a small transformer (generating a 4th octave overtone?). The modules are connected at the bottom by a main bus rail.

main bus pinout: (top to bottom) +297V DC pitch pot (+136..175V DC) vibrato envelope (about 2V AC, stabilized by a big "explosive candy" cap against GND) GND 32V AC 0V (?)

Even behind the tab switches are multiple such small transformers and further "explosive candy" caps.

When I examined the electronics, once the organ smoked badly and made no sound anymore; I guess I toasted the common pitch control potentiometer when its resistor at the 2nd bus line was accidentally bent against the grounded case. After I bent it back, the organ fortunately still works.

Behind the keys are lots of small resistors.

Here you see the metal lever under a key, which plastic end presses down 3 spring wire contacts. Behind the keys are the springs those hold them up.

At the right keyboard end is a small wire lever to clean the key contacts.

The leaf springs those hold keys up have all different strengths - I don't know if this is because it was a post- war product or because someone incompetently tried to fix stuck keys. (Initially mine had a few stuck keys, but the reason were bent metal levers and not too weak springs.) On the bakelite keys are many scratches; I guess that someone incorrectly stored the collapsed stand upon the keys when he transported the organ in its wooden carry case.