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Of all the strange myths that have grown up around Hammond organs over the years, there is one which is particularly illogical and decidedly unhealthy. It is this; that a Hammond organ is Immortal, and will continue to Live for all Eternity. The belief is that no matter how mistreated, or under-serviced, it will somehow manage to survive just a few more gigs. And if it has been oiled once or twice since manufacture, and has been occasionally polished, then it will positively live for ever. If you own a tone wheel Hammond, and find the concept distressing that your organ does have a finite life, then you may prefer to log off now, and avoid the painful reading that follows. This document is concerned with the increasing number of serious technical problems encountered by us in our renovation work. However well equipped our workshop may be, we are constantly obliged to wrestle with new difficulties. New renovation techniques have to be developed, which require specially made tools and machines, as well as hand made spare parts. The ever increasing demands on the Hammond renovation specialist is however only one aspect of the present situation; another aspect is to make Hammond owners aware of the problems to be overcome, if their organs are to survive. In this respect, there appears to be little or no help to be sought elsewhere on the internet, where information is usually what appears in old Hammond publicity material and service manuals. It is easier to understand why this 'keep-me-happy information' is so abundant, when one realises that the alternative is to consider the alarming nature of the truth. The small, unattended problems of the past became big problems, and more recently have become acute. In just a few years from now, most of the important models will have become so decrepit that they will be unplayable. Then, after a further period of neglect they will finally be discarded. It is simple to summarise the present day situation for models such as the A-100, the C-3 and the mighty B-3.
They are dying.


Mad Cow Disease
When production of the B-2 gave way for the B-3, Hammond made a change that was to prove fatal for the new model, after an incubation period of 40 years. It is like a disease that attacks the organ's brain, for thus could one liken the thousands of hair-fine resistance wires that connect the 1098 key contacts to the tone wheel generator. A long strip of self-adhesive dust excluder was attached to the inside of the angled protection plate covering the contacts from the rear, in order to prevent dust, dirt and other foreign material entering this very sensitive enclosure. From previously having being made of cotton felt, this strip was changed to an early form of foam rubber, which after 40 years has decayed into a black, sticky mass. Unfortunately, the products of decomposition are caustic, and the rotting strip is eating away the resistance wires where it is in contact with them. The lacquer insulation covering each wire has reasonable resistance to chemical attack, but having penetrated this protective layer, the process accelerates, and soon the wires are eaten right through. In no particular systematic order, certain footages on certain keys will cease to work, resulting from breaks in the resistance wires feeding the appropriate tones to those particular key contacts. One by one, more and more tones will disappear, making the job of reconnecting the ends become exponentially more difficult.

Caustic foam rubber residue on resistance wires

This magnified image, taken with special photographic equipment, should strike horror into the hearts of ABC owners. This is by no means a photograph of an exceptional case; every ABC organ that has been opened in our workshop during the last four years has looked like this. Using the match head for comparison, the thinness of the multitude of resistance wires can be appreciated. The different colours of enamel are codes indicating different specific resistances. The black bubbling mass at the bottom is the decomposing foam rubber. The caustic nature of this unpleasant substance reveals itself where a distinctive green tinge appears, as on the arching resistance wires that can be seen covered with it. Here, the protective enamel has finally succumbed to the aggressive chemical attack, hereafter the resistance wire itself is more easily eaten through. When attacked chemically, it is the copper constituent of the resistance wire alloy that produces the characteristic green colour, and such wires must always be replaced. On this particular manual, two wires were already eaten through, another wire disintegrated during the cleaning process and a fourth wire (the one shown in the picture) was so poor that it was removed and replaced. Organs are now turning up with many more than just four ruptured wires, and the situation is steadily deteriorating. There can be little doubt that what we term 'mad cow disease' is the greatest single threat to ABC organs, and it will be this, before anything else, that puts them in their graves.

As mad cow disease progresses, a secondary effect is bound to develop which is already in evidence here in Sweden, where an appreciable number of NGR organs are in existence. ABC instruments fall into a two distinct price groups on the open market, in which organs that are cleansed of the caustic strip are steadily becoming more valuable whilst those that have not are being avoided. It is very unfortunate that younger musicians, who would have the greatest long term benefit of NGR organs, are generally unable to afford them. Never the less, we would encourage any musician who is serious about his playing and his instrument, to make an NGR organ his objective, despite the unavoidably higher price.

The offending caustic strip on the inside of the covering plate. Note the indentation along the strip, where material has separated away and is now stuck to the resistance wires.

Both upper and lower manuals are affected on all models using the B-3 manual assemblies; A-100, B-3, C-3, D-100, RT-3, which we collectively term 'ABC' organs. This condition is slowly but certainly killing every ABC organ ever made - we have found caustic attack in varying degrees on every single ABC manual assembly that we have opened during the last four years. In several cases, wires have now been found eaten right through. The only cure is by prevention, whereby the manuals are removed from the organ, the cover plates are then removed from the manuals, and finally the strip is cleaned off from the cover plate and the wires. This process is one of the most complicated jobs imaginable; do not under any circumstances attempt it yourself. Job grade 5.
NGR organs have always had this strip removed from both manuals, followed by a thorough cleansing to remove every last particle that might remain between the wires.
The same unpleasant strip appears in several other models, being used to prevent rattling and buzzing between hard, adjacent surfaces. On the A-100 and E-100 it appears along the strong wooden cross member at the top rear of the organ which supports the lid, and if it is not removed, spreads infuriatingly when the organ is being worked on, soiling everything it sticks to. More seriously, it is used widely in the Concorde family as an anti-rattle measure, where it disintegrates into the electronics and causes corrosion. If neglected, these models will be as threatened in a few years time as the ABC models are now.

Piano Finger Blues
A old fashioned method of teaching young organists smooth and controlled hand movements when playing, was to place a penny on the back of each hand, where they would be expected to remain. How much longer the key contacts would last on Hammond organs if they were always played in such a gentle and fluid manner. Pianists however, when they leave their own instrument and turn to the Hammond organ, invariably fail to adopt the organist's flowing playing technique, and pound the keys with their characteristically violent and jerky movements. After much hard playing, this leads to the condition known as piano finger blues, characterised by worn out key felts and chopped up bus bars. The felts affected are those holding each key horizontally centralised, and when these become excessively worn, the keys flop without control from side to side. Even when played gently, adjacent keys knock against one another with a hollow clicking sound. [We are actively seeking help with developing a tool to accurately cut rectangles of felt, and a press to rivet them in place; please see document 'Can You Help Us?']
Far worse though is the damage done to the key contacts and bus bars. When a key is played, it pushes down a vertical stack of key contacts; on ABC organs there are 9 in each stack (one for each drawbar), on the E there are 12 and on the H there are 16! Under each contact lies a bus bar which traverses the whole width of the manual. Thus, ABC organs have 9 bus bars per manual, each 104cm long. They are made of a slim rod of tinned metal, having a cross-section which is sometimes square, and sometimes rectangular. What is remarkable about them is that a very fine wire or palladium lies embedded along the upper surface, against which the contacts touch when a key deflects them downwards. Despite the great hardness of palladium, wear will eventually develop in the form of a depression at the point where each contact (which is also tipped with a short piece of palladium wire) strikes the bus bar. The depression becomes a rut, and eventually, after much hard playing, the wire is severed. At this point, serious problems start to be encountered by the player. With the palladium wire now absent at the vital point, the key contacts have to make do with the bus bars' underlying material to make contact with, which is very unreliable due to oxide and dirt. Also, the palladium wire is prone to separating from the bus bar at the points where it is chopped off, and curls upwards towards the contact.

Palladium wire worn through, curling up and ready to short a tone on permanently.

When the wire reaches the contact, a tone is switched on and is impossible to get rid of, except by never using the drawbar to which that bus bar is attached. If the oxidised and unreliable key contacts tempt the player to use the bus bar shifter, which slides all 9 bus bars sidewards, all the curled up palladium wires find a contact to short against! Not only that, but all the contacts will then be poised above areas of the bus bars that have an accumulation of 35 years of dirt and hardened bus bar grease on them. Suddenly, half the keys will ceased to work at all, whilst a number of the rest may sound continuously. Clearly, there are lessons to be learnt here.

  • If pianists are to play Hammond organs, it is vital to the length of life of the manuals that they play gently. The two-pennies method may help.
  • Do not touch the bus bar shifters. It is many years since this was a safe cure to use.
    If is known that a particular organ has not been subjected to heavy playing, but it never-the-less has unreliable key contacts, this is probably due to dirt and hardened bus bar grease. If the manuals have been removed from the organ for the removal of the caustic dust excluder strip, this is an ideal opportunity for cleaning and re-greasing the bus bars. Any organ being renovated at our workshops which show signs of contact problems is always inspected. Dirty bus bars are cleaned and greased, while worn ones are replaced with our own solid precious metal bus bars. Job grade 5.

Setting the Spirits Free
An elementary discovery when working on Hammonds is the fascinating effect of treble boost. All sorts of pops, wheezes, fizzles and clicks emerge from the Leslie, and the organ's sound assumes a wheezing quality similar to one's voice after downing a large glass of cheap whisky. The effect tends to over-emphasize the unevenness of the basic 91 tones, and eventually becomes rather tiresome. This is especially so with the older tone wheel models, which have the older beige/yellow coloured generator filter capacitors.

Generator filter capacitors of this older type must be replaced.

These capacitors are now so very inaccurate (they are supposed to be within 1%) that the unevenness and breathy sound is disturbingly predominant, treble boost or not. This is how the capacitors play their role; the signal from each tone wheel and pickup assembly is far from pure, and contains a host of overtones, undertones and signals leaking in from other pickups. From frequency 44, these impurities are deemed to be so disturbing that filters are used to 'cleanse' them. From 44 to 48 each signal passes through a small transformer whose inductance is sufficient to trim off overtones. From 49 to 91, a capacitor is added to each transformer, forming a tuned circuit which boosts the wanted frequency and rejects all others. This resonant circuit reacts to a specific frequency determined by the resistance and inductance of the pickup and transformer, as well as the value of the capacitor. When the mathematics are correct, the frequency of this resonant circuit coincides exactly with that of the tone wheel. But this clever balancing act of electrical parameters collapses when the capacitor's value starts wandering. As the old style capacitors age, their values increase greatly - we have recorded increases of up to 200%! - causing poorly tuned resonant circuits which produce weak and impure signals. The newer, maroon red capacitors do not exhibit this tendency to the same extent. Since all the individual circuits are different, special equipment is required to determine the optimum capacitance for each, after which capacitors of the appropriate values are installed. This immediately has two effects; one is mathematical and the other one is more spiritual. Firstly, as if by magic, all 91 outputs from the generator fall exactly into their correct relationship to each other. Secondly, the astonishing clarity of sound produced by this operation is probably what prompted the comment about the sound quality of an NGR A-100, likening it to the view from a mountain top after the fog has risen. There remains, however, an impressive grand finale, for now is the right time to add treble boost. A truly spectacular organ sound emerges revealing a degree of soul and character that only a tone wheel Hammond could produce; it's spirits have been set free.
For owners of older organs with the yellow capacitors, this is a very rewarding job to have done, but it is tedious and complex work. The generator must be removed from the organ, the old capacitors must be carefully removed, scores of measurements have to be made, and then the new capacitors are installed. There is a serious hitch that can arise, which is impossible to foresee if the organ's history is unknown. Someone else may have compensated for the uneven pick-up signals (arising from the inaccurate capacitors) by altering the adjustment of the magnetic rods. If so, recalibration will then be necessary after replacing the capacitors. This job, apart from requiring special tools and equipment, calls for a degree of experience. Without calibration, job grade 4. Including calibration, job grade 5.

Hammond Graveyard
On a very high pallet shelf, reached only by a forklift truck, stand the up-ended carcasses of half a dozen sawn-off L-100s. Mindful that such a sight may offend the sensitivities of visitors to our workshop, these pitiful reminders of the 70's lust for Hammond dismemberment remain half hidden. If a customer should enquire if we supply split Hammonds, Marley's ghost of Hammonds-past reveals this graveyard with his pointing finger, and says in an unearthly voice, "Beware!"
The homemade split L-100 must surely be the organ engineer's most detested organ.

A so-called split (i.e. ruined) L-100. Why did they do it?!

Even if the amputation was conducted with surgical precision, which they almost never are, there is a host of reasons for holding these abominations in such contempt. To avoid dwelling on a long and tedious list of problems that might resemble a list of charges read out as a prisoner was led away to the gallows, let the point be proven by the existence of our L-100 graveyard. If you are looking for a Hammond, and a sawn-off L-100 turns up, our advice is to avoid it at all costs. There are, however, two factory-made split L-100s, the Porta-B and the L100P, which were designed to be dismounted and moved from gig to gig. It is doubtful, though, that the musicians using these models would entirely agree with Hammond's notion of 'portability'.

Leslie Cabinets
No-one would question the immense improvement to the sound of a Hammond organ brought about by connecting it to Leslie cabinet. But these too are ageing, and many are in urgent need of attention. For those who are reasonably handy, there are several service jobs which can be done at home by the owner, and details of these are found under Care of Leslie Cabinets. In common with Hammond organs, ever more problems are being encountered, some of which the owner could tackle himself, and some which he could not. In particular is the increasingly poor state of the motors, due mainly to insufficient lubrication. Whilst moderate wear can be taken care of with a thorough service (grade 4 job), severe wear can only be solved by replacing the axles and bearings, along with all the numerous different washers, spacers and springs. (Job grade 5). By comparison, problems with the windings are infrequent, and if more than one motor is burnt out in the same cabinet, this has usually been caused by the inadvertent connection of 110volt motors to a 230volt supply. When it comes to the speed control systems, a giant blind spot is exhibited by both those who designed Leslies and those who use them. It is incomprehensible how such a crude, dangerous and noisy arrangement can have been left unattended for so long. Not the slightest glimmer of modern technology entered the arena until the arrival of the model 760, which was unjustly greeted with derision rather than admiration. [The 760 and its superb walnut counterpart, the 770, have a remarkable number of virtues; after upgrading work has been carried out, they form the basis of our top-of-the-line Master Class series]. The mechanical clicks from the relays in the older models can be very distracting in quiet playing environments. If sensitive audio equipment is nearby, this is prone to picking up electrical interference from the relay's sparking contacts. There is also the question of the relay's terrifically high control voltage, whose magnitude has more in common with a Van de Graaf generator than a musical instrument. Since the task of developing a modern replacement for the old relay system is usually beyond the owner, the responsibility here is on the organ engineer, who should be routinely performing this operation on all Leslies passing through their workshop. We use thick film solid state relays incorporating a zero crossing switch, with a 5 volt control system, and have not sold a Leslie for 13 years without replacing the old system.
Age is now taking its toll on the Leslie's audio system, as well as the mechanical components. The increasingly poor treble response of the V-21 driver is misinterpreted as 'charming softness'. The reality is that old age, oil from the treble rotor, and heat from the speech coil, are all contributing to the gradual deterioration of the membrane's phenolic material, whose high frequency performance diminishes as the membrane loses its suppleness. For use at home or in churches, the V-21 may still have its purpose, but the final phase of 'setting the spirits free' consists of replacing the old driver with a newer alternative having better efficiency, especially above 5kHz. In addition, the greater power handling capacity of modern drivers is useful, considering the greater volume levels common today. To fulfill the requirements of certain stage musicians for very high volume, we use two large, high efficiency drivers in a twin adapter. For more volume, we would recommend double Leslie cabinets, and if even more volume than that is sought, we would advise seeing a hearing-specialist! There is an odd problem now creeping into the picture, which places undue strain on the treble driver - the cross-over network of the older models incorporates a double paper capacitor, the value of which is now gradually rising (in the same manner as those on the tone wheel generator filters). This upsets the careful balance of the network's components, causing bass to leak into the treble circuit. The intended cross-over point of 800Hz is very low for a treble speaker to manage at all, and lowering this point still further places great strain on an old driver. This capacitor should be checked. De-solder the red and black wires first. The two values should be 7.8uF and 12.5uF, and if these have increased by more than 20% or so, they should be replaced. Modern bipolar capacitors are quite good enough, and their low price allows bunching several together to achieve the correct values. (Use 4.7uF + 3.3uF and 10uF + 2.2uF. 50volt rating is sufficient)

50Hz or 60Hz? BEWARE !
Just as, say, a diesel engine differs fundamentally in its properties and principals from a petrol engine, so did Laurence Hammond's newly invented synchronous motor differ fundamentally from existing electric motors. The property underlying its uniqueness was the ability to maintain an absolutely constant speed, this being determined by the frequency of the mains electricity powering it. Used to drive his electronic organ, (which he invented to create an application for his motor) Hammond could guarantee that the organ would never need tuning since all the spinning tone wheels were mechanically coupled to the motor by a system of cog wheels and axles. In the USA the mains frequency is 60Hz, and all Hammond's design calculations were based on the rotational speed of his motor when powered by this supply. Following the immediate success of his organ, Mr. Hammond's prudent sense of business led him to initiate export to Europe, and after some furious work on his slide rule to recalculate his designs, export versions of his organ were soon on their way to Europe. The 50Hz mains supply in Europe would cause his motor to rotate at a slower speed, so all the cogs and axles would have to be reworked to compensate for this. The start motor would have to be different too, as well as the flywheel and the tremulant generator and the vibrato scanner, (the latter two features appearing successively in later years). As early as 1936, the icebreaker cargo vessels of the Aga Baltic Company were docking at Stockholm's frozen wharves, where they offloaded Hammond organs entirely adapted to the European 50Hz electricity supply.

50 Hz versions existed as long ago as 1937.

Considering, then, that as long as seventy years ago the problem of 50Hz contra 60Hz was solved competently and elegantly by the organ's own creator, is it not beyond belief that 60Hz organs are still finding their way to Europe by dubious means, instead of staying where they should be; in the USA ! ! Once having landed on these foreign shores, these poor 'illegal immigrants' have to suffer the indignity of hideous back-street botch jobs to convert them to 50Hz, after which they are sold to gullible customers who are unaware of their low value. All the electromechanical components are different - the synchronous motor, the generator, the start motor, and the vibrato scanner, and 60Hz spare parts are unavailable in Europe, should work ever have to be done on them. If you are considering buying a Hammond tone wheel organ, avoid being the 'gullible customer' - insist on seeing the organ's registration plate. If it says 60 Hz, beware! Be especially suspicious if the plate is 'conveniently' missing or has been tampered with. Remember, there is no shortage of Hammonds in Europe, so buy a 50Hz model. There is, however, a shortage in professionally renovated tone wheel models.

Danish Pastry 760
The Danes are Germany's nearest neighbours to the north, and are much esteemed for the quality of their foodstuffs. The beer is tasty, strong and sparkly, the pastries are crisp and not over-sweetened, the butter is creamy and rich, and the bacon is smoked, savoury and sizzling. Understanding the economic prudence of industrial diversification, the 1970's saw an eager redirection of the Danes' skills to an area quite new to them; making Hammonds and Leslies. The Danish importer, Bröderna Jörgensen, must have been gifted with a great talent for persuasion, and struck an unconventional deal with the Chicago directors, enabling themselves to import Hammond bits and Leslie pieces, using them as they saw fit. With a surprising lack of Danish style and design, a range of seriously ugly boxes were conceived, into which the unfortunate imported components were forced. Mercifully, most of these special Bröderna Jörgensen models have succumbed to euthanasia, but those managing to escape are still blighting the names of Hammond and Leslie to this day. Known as the 'wienerbröd 760', their version of the Leslie 760 permanently ruined the reputation of this model in Scandinavia. Believing that Leslie cabinets' meagre slits stopped the sound from emerging, they hacked out the vital louvres, leaving the two rotors open on three sides. The smooth swirling sound was gone, replaced by a staccato bark. The inferior handles which they adopted soon wore loose, providing an involuntary accompaniment like castanets. The skirt at the bottom, concealing the cabinet's castors and other private parts, was removed. Inside, so called safety measures produced horrors like un-insulated fuse holders at mains voltage, and an isolation transformer completely lacking hum-field shielding (which was also incapable of holding output voltage when it was most needed - at full power). This awful list goes on, but the message is simple; in general it is wise to avoid Hammonds and Leslies bearing the Bröderna Jörgensen label. If, however, you already own a wienerbröd 760, please read the following carefully.

(a) Three un-insulated fuse holders are placed on the metal side of the power supply chassis, which is screwed to the floor of the cabinet. The 5mm spacing between these fuse holders is very unfortunate, being exactly that of the fuses themselves. If you have to replace a fuse, always, always pull out the mains plug first! Then check visually that you place the new fuse correctly in its holder, and not in the space between two holders, in which case the metal caps will form a direct short in the power circuits, and they are no longer protected by a fuse! BANG! Fetch a torch, get on your knees, and watch what you are doing.

(b) The lack of louvres degrades the sound pitifully, but you can improve things yourself by installing sound shields. Cut out six pieces of hardboard, all slightly longer than the rectangular openings where the louvres are supposed to be. Screw these to the inside of the cabinet, using 7mm spacers to create a gap between the hardboard an the cabinet, so shielding off the rotor's direct sound, but providing an exit slit for reflected sound. The spacers at the centres of the treble shields must be less than 7mm, or the rotor will scrape just there. Job grade 2.