Electronic organs - circuits, experiences and interests

[Lucien Nunes]

Can I talk about vintage electronic organs here? There are forums specifically about organs, but they tend to be focused on the playing and the music rather than the technology inside, and usually oriented towards US-made models whereas my collection is mainly UK-made.
If anyone is interested in how this stuff works, I will gladly document things as I go along. It will be a slow burner of a thread as these things take a while to work on.

To set the scene, although I have more radios than organs, the sheer size of some instruments means that the collection of 44 organs is physically one of the biggest sections of the MEET collection, at the moment divided between three locations. Many are not accessible to play or work on, and as I consolidate and organise the stores this spring, I want to rectify that in preparation for whatever ultimately happens with MEET, which in turn depends on my health. So, I need to get cracking; restoring, repairing, documenting, in readiness for a grand demo. The core of the collection is a range of over 20 models of Compton Electrone, the only such collection in existence, including models of which no other examples are currently known. Others are included to compare and contrast, e.g. showing how Miller did with electronics what Compton did with electrostatics, and how Hammond did the same with electromagnetics. As a result, a variety of technologies are included:

* Valve oscillators throughout
* Valve top-octave oscillators plus frequency dividers
* Transistor top-octave oscillators plus frequency dividers
* Rotary electrostatic generators
* Rotary electromagnetic generators
* Reed electrostatic generators
* Analogue LSI IC dividers

To start off - a look at the front and back of a Compton 3M/E, a relatively high-spec although rather quirky home entertainment model from the mid 1960s. Based on their most basic rotary electrostatic tone generation system, everything is built into the console including the speakers, as standard on home models. Number built unknown, probably a few dozen. This is one of two currently known to exist, although there might be a few more sleepers. A 3M/W with decorative sides is seen briefly in the Beatles' film 'Help.'

Please do add anything interesting about any kind of electric organs, it doesn't have to be Compton related.
   
   

[Mike Watterson]

Even most of the acoustic pipe organs have keyboard & stop electrical switches, solenoid electric valves at the bottom of each pipe and an electric motor for the air supply. I repaired the valve wiring and the motor on on one a couple of times. In both cases it was corrosion due to damp in the church. I varnished as much solder joints and bare wires I could access. All the wiring was individual solid copper enamel wire apart from the mains. I never found where the solenoids were powered from. It also has a motor driven revolving baffle option, I guess a sort of tremolo action.

I was given a couple of 12″ speakers apparently from a scrapped electric or electronic organ about 25 years ago that I built into reflex cabinets with 6″ driver (infinite baffle) and horn tweeter on top of the reflex box.

The steam organs are amazing. I presume purely mechanical keyboard to valves connecting steam to pipes.

[peter scott]

When we were in the US some years ago we made a point of visiting the Atlantic City Convention Hall on the boardwalk knowing that it had one the world's largest pipe organs (33,000 pipes). The hall itself is the size of a football pitch.


We were very fortunate to meet the organist who is in charge of its restoration and he gave us a guided tour as well as a short performance.



To give you the scale, the organist is located in the  drum shaped booth to the right of the stage. The people in this photo will also help with the scale.





https://en.wikipedia.org/wiki/Boardwalk_...rium_Organ

Peter

[Diabolical Artificer]

It's an interesting subject Lucien, I was researching this recently whilst looking for valve oscillator circuits for an idea I had. The idea was basically a one octave LF keyboard, a bit like a sub Fender Rhodes bass keyboard but lower frequency, eg 16.35hz & up. I tried a phase shift oscillator but that wasn't a success, it was too hard to adjust & the sine wave was distorted. I couldn't find a simple valve oscillator so experimented with a op-amp wein bridge oscillator adjusted using 10 turn presets. With that I could dial in the frequency so it was bang on.

I saw how Hammond did it, IE with notched disks and pickup's, this would be hard to do DIY as there's to much engineering brackets etc. I saw some Lowry organs that looked like they were using individual oscillators and also at the Thrytone that used thryratrons, I've yet to try those oscillators but the thryratron idea looks interesting.

The other tricky bit as regards organs is the keyboard, the action of the keys themselves. I think Hammond used a "waterfall" key & each key had multiple contacts that engaged with bus bars. Hammond keys are clever in that the spring contact slides as it makes contact, the idea being that this action cleans itself ridding itself of any potential oxidation or carbon.

I could be wrong on some of this, my research was brief, so this thread is very timely, i look forward to more. Andy.

[joebog1]

I have some experience with Hammond organs and Leslie speaker boxes.
I have paid money to see the "big " organ in Sydney town hall, but the bottom two registers cant be played as the "experts " are worried that the low frequency will collapse the floor.
The floor just happens to be to roof of Town Hall Railway Station.

BRILLIANT piece of Australian engineering!!! .

I do love a really good organ recital, something similar to an excellent and large choir.
NOTHING can approach the actual sound they can create.

Joe

[Lucien Nunes]

Even most of the acoustic pipe organs have keyboard & stop electrical switches, solenoid electric valves at the bottom of each pipe

This thread is mainly going to be about electronic organs, but I will touch on the subject of electric action of pipe organs for a moment as it's been raised. Historically, pipe organ action was purely mechanical - pressing the keys opened wind pallets, drawing stops opened the sliders. Indeed, purely mechanical 'tracker' actions are still used, and favoured for some styles of organ and playing. In the 19th century, tubular pneumatic action enabled the console to be remote from the windchests and allowed for various control functionality. But it was the coming of electric action in the 1880s, and especially from 1900 onwards, that enabled many new functions and developments. One of the early proponents of this fusion of electromechanics and organs was Robert Hope-Jones, younger brother of Frank (of Synchronome fame) who did the same with electromechanics and clocks. The cinema organ, in particular, owes much to Hope-Jones's efforts to use electricity to elicit more versatility from a given number of pipes.

Later on in the thread, I will give you a tour of the extensive electric workings of a really large, complex pipe organ. I am privileged to be responsible for maintaining the electrics of the 1937 Southampton Guildhall Compton, one of Compton's masterpieces of unique design that fulfils the roles of both classical and entertainment playing and has about the most diverse tonal palette of any in existence. To offer the organist the most suitable facilities and performance environment for any style of music, it has two fully equipped 4-manual consoles of completely different design, layout and stoplist, both controlling the same pipework; one optimised for entertainment and light music, the other for classical repertoire. Behind this show of mutifarious flexibility is a substantial organ of 50 ranks, many highly extended, voiced to a high standard and also equipped with an original 'Melotone' electronic tone generator.

Unlike many organs, it has not been modified, expanded, contracted, tinkered with, revoiced, relocated, re-imagined... or any of the many things that often befall organs as fads come and go and musical opinions change. It is exactly as Compton built it in 1937, with all of its original pipework and actions. On the electrical side, the only modernisation done has been to replace a few hundred feet of perished rubber wiring. Thankfully, rubber insulation was only used on about sixty runs from the windchest common negative terminals to the main distribution blocks. Most of the wiring is cotton covered and in perfect original condition.

So, some electrical stats to make you sit up and think. These numbers are top-of-head and approximate:

3,650 pipes each with its own electromagnetic armature valve (called a 'chest magnet' in organ parlance.)
7,000 electromagnets / solenoids total, including relay coils, chest magnets, stopkey units etc.
552 keyboard keys each making up to six contacts.
> 50,000 contacts total including relays, matrix relays (multiplier-adders), memory units etc. Some relays up to 61 poles each.
>100 miles DCC (cotton covered) wire.
4.5 kilobits of non-volatile electromechanical binary memory for combination piston settings.
Action powered at 18V from motor-driven dynamo, 100A continuous output, 250A peak.
Audio output from 'Melotone' electronic tone generator section via 4x PX25 and dual-driver Vitavox horn.

Enough pipe organ stuff already, tomorrow I'll pick an electronic and tell you about it.

[joebog1]

3650 pipes!!!. No doubt brass or a similar alloy. Sounds a real chore to polish them !!.
61 pole relays !! thats a few extra for transmit/receive switching. I can only imagine the wiring under that monster.
Not to mention the power required to "push " all those contacts together.

18 volts @ 100 amps is a moderate sized mig welder !!.

Joe

[Ed_Dinning]

Going back, there were some good designs in PW and Radio Constructor from the 50's; but on nothing like the scale of the above beasts!

Ed

[Lucien Nunes]

Right, back on topic with electronic organs. This one is not so historic, but it's a good'un, a Wurlitzer 950TA from 1979. Top model in their range at the time, right at the end of the analogue era. I got it for dad about 15 years ago, bought online for one pound. Ludicrous, considering it cost a five-figure sum new, but there are two clear reasons. One is the glut of home organs available second-hand at the moment, as many were bought in the 1960s and 1970s by a generation no longer with us. Their successors are not so likely to be players, and few of them will give space to 'grandpa's organ' any more, so home organs are widely available second-hand. Granted, not many of them are of this calibre, indeed many are mediocre, but with the larger instruments of this age comes teeming complexity and maintenance headaches and that is the second reason that buyers who simply want to play music are unwilling to shell out for them.

I bought this knowing it to be faulty, expecting it to be very faulty in many ways, and I was not wrong. The actual number of faults present on arrival now escapes me, somewhere between 20 and 30. The previous owner had tried to get it repaired, but could not find an organ technician prepared to tackle it at all, let alone at a practical price. Such techs are thin on the ground now; they know that these behemoths have ongoing issues with unavailable ICs, recurrent contact problems etc, so it's unsurprising that they are considered borderline unserviceable. I.e, enthusiasts' territory only, not a realistic commercial proposition.

Given the component-count, it is not the kind of thing you could or should 'shotgun' repair; certainly not something you would enjoy re-capping as a precaution. A barely-legible photocopy-reduced service manual was going to set me back £50 so I decided to try and live without one, as I had some prior knowledge and experience with these and similar models. As things turned out, most faults were bad semiconductors including leaky transistors, dead CMOS switches, opamps, bucket-brigade delays, and some shaky soldering and PCB damage from ham-fisted repairs in the past. At that time, thankfully, none of its few dozen custom LSI ICs was faulty and there were no ususual parts to source. I ploughed through it one fault at a time in the workshop, got it 100%, and with some effort six of us carried it up the stairs and squeezed it through the front door into the house.

Dad and I had some fun with it over the years, during which a few further repairs have been done. Since I've been ill, the faults have been gaining on me; there are now half a dozen, of which one or two are rather elusive and subtle. Indeed, if one didn't know exactly how a 950 was supposed to sound, one probably wouldn't spot them. I will come back to those in the next instalment but first a few views of what's inside, or at least what you can get at by folding things up layer by later. There's more hidden round the back and in the pedestal, but I'm not pulling it away from the wall until ready to start the repairs.

[joebog1]

LOvely thing!!!! Show this to a board jockey that does computer repairs ( changes everything ).

I still have a solid state ( well sort of ) Hammond with horrible decade dividers. I forget the number, but they are exclusive National Semiconductor.
It was given to me because the chips are elusive. When you do find one it will be ex equipment from another organ "maintainer " and will probably be similar
to the one I need. Its missing all F keys. ( I forget the note, but you get my gist ) All octaves worth.

The other thing is the number of contacts for the keys. The more complex the organ, the greater the number of contacts.

My organ was on the road for many years, and had the mandatory flat black paint overhaul of the otherwise nice woodgrain laminex inserts.

I have the foldup stand and pedal clavier and its your free. IF you can carry it.


Joe