Oldest Allen MOS Organ I've ever seen

[jbird604]

A few years ago we got this old MOS organ in trade. It had been in the same church ever since purchased in 1971, and they finally wanted to upgrade to an ADC-3100 we had in the shop. So we got the old MOS organ and just pushed it against a wall. It was SO old, I thought, and so simple and basic, and I feared it might not be reliable enough to re-sell it. Besides, it's pretty hard to find a home for an old digital organ with such plain sound and with none of the features that people seem to want -- it has no capture action (only 3 blind presets), one expression pedal, no crescendo, no card reader. So, as plain as they come. And no celeste, no chimes, no 32' pedal stop. Not very appealing.

Well, this week, I had a young man message me on our Facebook page. He plays an Allen Protege in a church and needs a real AGO organ at home for practice. Asked what we had for very little money. I offered him this old MOS for $500, as-is-where-is. He came and got it today, and is apparently delighted. I'm happy it found a home.

As we were prepping it early in the week, I took note of just HOW OLD it is, as MOS organs go. I noticed that the sockets for the MOS board and all the other boards of the MOS system are hand-wired, not mounted on the "motherboard" or "frame" that Allen designed for the MOS computer system very early in production. It must be one of the first few hundred produced, perhaps one of the first few dozen. Just barely removed from the prototype!

Also, I noted that the key bed is a hefty block of wood reinforced with angle-iron. And the key contacts are hand-wired with loops of heavy yellow wire, instead of being mounted on a PC board, as they have been since quite early in the MOS era.

The KBA and SBA boards are built with nothing but discrete parts (no IC's, just ordinary transistors and resistors and such). And the presets operate old-fashioned mechanical relays, just like the preset systems in the plainest old analogs.

Even the pedalboard is heftier and sturdier than what we see on current models, with a thick and firm felt cushion for upstop and downstop material. and the pedals still have that firm, new organ feel, as do the keys!

So, did I just give away what amounts to a "museum piece?" Possibly so, but I'm just glad that a young organist will be getting the use of it. And it's built like a tank, so should last him for many years.

[rjsilva]

That’s neat! Thanks for sharing. As I was reading I was imagining that it may have been a proud endeavour for Allen, with excitement about this new technology, taking a ‘chance’ on something new.

[davidecasteel]

If he wanted to in the future, could a card reader be retrofitted?

David

[jbird604]

Adding a card reader would be expensive and tedious. A different clock board is required (the card reader scanning logic was put on the clock board, just because there was space for it there), as well as an upgraded MOS board and the card reader itself. The power supply for the CR lamps would have to be added, as the standard version of the MOS power supply lacked that supply. And then there's the wiring for it all.

Much cheaper and faster to add a MIDI interface, such as the Harrison Labs board that simply clips to the KBA with a few wires and MIDI's up each division with a separate MIDI OUT jack.

[Al Offt]

John,

When reading your original post, I thought you were describing my Allen organ. I brought a model 120 (serial AC-440) back in 1972 but its inners were "upgraded" in 1986 after a power surge (power supply, MOS board and both amplifiers IIRC) and more recently the keyboard encoder board (2017). Unfortunately it is currently waiting for repair with only the 16ft and mixture stops providing any sound in both Swell and Great organs.

I use it as a practice organ and it sounds quite acceptable in a 12 x 24 ft living room. I particularly like the selection of stops which, I believe, are close to those used in the Baroque organs of Northern Europe.

[voet]

Alan,

I think you have to go quite far north in Europe to find baroque organs

with only the 16ft and mixture stops providing any sound in both Swell and Great.

:-)

[jbird604]

Pretty much the same organ, but the System 200 is self-contained. Allen made more or less the exact same organs from 1971 through 1983 with relatively minor changes over time. Even the changeover to MOS-2 was only a repackaging of the same technology, incorporating all the useful options and extras that had appeared over the years in the MOS-1 lineup.

BTW, the reason you only have 16' and mixture stops -- these are the only stops that are NOT addressed via the SBA ("Stopboard array"). Instead, these stop tabs run directly to the MOS board, where each one simply grounds a certain pin, turning on that wave shape. The other stops evidently are missing because your SBA board is out of order.

I haven't looked into the technical reasons why this is so, but the same weirdness was carried over into the MOS-2 system. In that system, all mixture and "sub-octave" stops (16' and 32' and any desired custom stops) were contained on EPROM's instead of being in the system ROM, and were addressable only by directly grounding a pin on the MOS board connector.

Perhaps it had to do with a binary limitation within the SBA circuit. Since the MOS stoplist always had at least 36 stops, and the SBA has only 32 inputs (4x8 matrix), they had to do a workaround to make it possible to include all 36 of the stops that Markowitz and others at Allen insisted on having in the original MOS spec. The next step up in binary would've been 64 inputs on the SBA, which was way overkill.

Just a guess though. Nobody's ever told me that.

[myorgan]

So, did I just give away what amounts to a "museum piece?" Possibly so, but I'm just glad that a young organist will be getting the use of it. And it's built like a tank, so should last him for many years.

John,

I wonder if it was the 4^th organ in the 500 series, or it was actually the 504^th organ made? Either way, it is certainly a piece of history. Thank you for sharing the photos!

Michael

[jbird604]

Curiously, the serial numbers may not actually be sequential. For example, the System 200 I had is almost certainly older than the System 120 that Al Offt mentions up above. If I'm not mistaken, the 120 came out in the second year of MOS production and has the Random Motion board, which the 200 does not. Yet his serial number is 440 and mine is 504. Of course, Allen has always bounced around serial numbers, at least since the digital era began. When the "T" console was introduced, they started a whole new sequence of serial numbers for the various models built in the T. And nowadays, there are "KT" and "L" and other prefixes on serial numbers.

It's possible that Allen pre-assigned blocks of serial numbers, with the 200 series starting at serial 501. The one I just sold would then be the fourth one off the line, which really makes perfect sense, given the primitive nature of the wiring and other details. I do know that it was sold and installed with the "slow-motion" gyro cabinets (discussed in another thread recently -- the gyro turned VERY slowly, about one revolution in two seconds). But I did not get the original cabinets when I took it in trade. They were just too big and heavy to try getting down from the chambers, and I didn't want to use the SawsAll on either the chamber or the speakers! I'm pretty sure the slow-motion gyros were discontinued after the first year of MOS production, as soon as the Random Motion board was incorporated into the design.

[myorgan]

It's possible that Allen pre-assigned blocks of serial numbers, with the 200 series starting at serial 501. The one I just sold would then be the fourth one off the line, which really makes perfect sense, given the primitive nature of the wiring and other details.

John,

That was my thought when I posted. I know with the earlier Fender electric guitars from the 1950s, the serial number plates were printed and put in a box, then the person at the end of the assembly line would pick up a random plate and put it on the guitar. For that reason, it's very difficult to accurately date a Fender electric guitar based on the serial number alone. Method and mode of manufacture are used more often than the serial number. It occurred to me that might apply to Allen's earlier digital organs as well.

Michael

[jbird604]

That may well be the case.