Hammond M102

Tab Mechanism

2009-09-18T23:42:00.003+01:00

The two sets of preset tabs have a mechanism which prevents two tabs being selected at once. This is made from various brass levers and pivots, and is located immediately behind the tab switches.

This mechanism requires lubrication, otherwise the tabs will stick or be very stiff to operate.

Dismantling the mechanism is the best way to apply grease. Only a thin film of grease is required, but it should cover all of the moving parts. Electrical contact grease was used, same as for the drawbars.

The set of images shows the assembly sequence. First, the three small brass levers are placed on the pivots. Two round brass spacers go on the two pivots near the bottom of the picture; note the left spacer is thicker than the right one. A third spacer goes on top of the rightmost brass lever.

In the second image, a larger brass lever is placed over the right and centre small levers.

The third image shows the second large brass lever which covers the rightmost small lever and the centre section of the previous large lever. Two additional spacers are added, these can be seen to the left of the picture.

Finally, the top lever goes over all of the others. Two small brass tabs secure the whole assembly in position. These should be tight enough to hold the levers down, but still allow the parts to move easily when the different preset tabs are pressed.

The Vibrato/Chorus tabs have a similar mechanism, although this is simpler, covering three tabs rather than four.

Vibrato repaired

2009-09-07T19:36:00.002+01:00

After some investigation, the failed vibrato was a single 1M resistor which had gone open circuit. This resulted in the vibrato preamp not working at all.

It was possible to replace the resistor without removing the amplifier from the organ, and the vibrato now works perfectly.

Tab contacts cleaned and lubricated

2009-08-31T20:35:00.003+01:00

Other items which have been done are the cleaning of the contacts on the tabs. This picture shows the rear of the tab assemblies, the top of the organ has been removed and the frame holding the tabs lifted up and tilted to allow access to the drawbars.

The switch contacts are clearly visible behind the white plastic tabs. The drawbars are to the right of the picture below the 3 white tabs, and the round can object is the variable capacitor for the pedal drawbar.

The contacts are easily cleaned using a contact cleaner spray. Note there are various types available. The first type to use is one which does not leave any residue. This will dissolve any grease, oxides or other dirt on the contacts. A compressed air spray will remove any dust and dirt.

After cleaning, it is essential to apply some lubrication in the form of a contact spray which leaves a lubricant behind. Without this, the contacts will wear away quickly. This must be a lubricant designed for electrical contacts.

The tabs where only one can be selected at once have a mechanism behind them made from various brass levers and pivots. This also needs lubrication, otherwise the tabs will be very difficult to operate. Electrical contact grease is ideal.

The drawbars have also been cleaned and lubricated in a similar way.

Reverb Amp

2009-08-31T20:28:00.004+01:00

As mentioned earlier, the reverb amp has a distinct mains frequency hum when either or both of the reverb tabs are on. Further investigation reveals this is from the amplifier itself, rather than any of the associated wiring, reverb tank or the controls.

This will either be a bad valve (tube), or old and faulty capacitors. The electrolytic capacitors are most likely, given they are nearly 45 years old and well past their expected lifespan.

I'll be replacing these shortly, and also replacing the caps in the main amplifier as well.

While the main amp is out for capacitor replacement, it should be possible to fix the faulty vibrato as well - probably a failed resistor.

Further problems

2009-08-19T00:05:00.003+01:00

Now that the generator is practically silent in operation, certain other faults are noticeable.

There is a 50Hz hum on the Reverb section, only present when one or both reverb tabs are on. Clearly picked up from the mains supply somewhere so probably a poor connection or failing capacitor in the reverb amp or reverb circuit.

The Pedal drawbar is noisy when moved, probably just dirty contacts.

A couple of keys on the upper manual have intermittent contacts, only apparent on some drawbars. Busbar shifting may fix this.

In addition to these minor problems, the Vibrato system has almost completely failed. With vibrato selected the volume is dramatically lower than normal, and serious distortion occurs when two or more notes are played. This is probably a bad valve (tube) or contact somewhere.

The scanner appears to be working as when playing just one note the sound is correct although much quieter than it should be. (The note is barely audible even with the 'volume soft' tab off and the swell pedal wide open).

The vibrato was working properly only a few days ago, so this is a very recent failure. It's not over oiling either, since only a small amount of oil went into the scanner tray, and the scanner is still working.

Unfortunately, failures like this are inevitable with 40+ year old electrical equipment.

The next repair will be to clean and lubricate the tabs and drawbars once some contact cleaner and lubricant is obtained.

Stuck wheel fixed

2009-08-12T16:16:00.003+01:00

The jammed tonewheel has been fixed, it was simply lack of oil. The wheel was moving, but not at the correct speed, and it causing some vibration which completely destroyed the note it should have been producing. Applying oil directly to the bearings resolved the problem.

The tonewheels can be accessed by unhooking the support springs at each corner of the generator so that it rests on the wooden shelf, then tilting the whole assembly upwards. Two blocks of wood under the front edge support it in position.

The jammed wheel was number 72, which is near the centre on the back of the generator (nearest the front of the organ). Oil can be applied by using a small brush or wooden stick.

Plenty of oil has been put in to the generator so it will reach the many other bearings in a few days or weeks. Although a 4oz bottle in theroy has enough in it for 8 years, (0.5 oz per year), this assumes that the generator has been oiled regularly. This one clearly has not, there was no evidence of oil anywhere.

The modification has been removed, as the starting motor and mechanism works perfectly now that it has a small amount of oil on it.

Starting Motor

2009-08-09T23:49:00.003+01:00

This is the other end of the generator. The small starting motor is located in the centre.

The unwanted modification can be seen here also, the block of wood attached to a metal rod. This is useless, and will shortly be removed.

The front of the generator has a red label with the serial number, this is the same as the serial number on the outside of the cabinet.

Note also the springs holding the generator above the wooden shelf. This is to prevent noise from the motor being amplified through the wooden casing.

The generator can be bolted down onto the shelf to prevent damage when transporting the organ. One of the four bolts can be seen at the bottom right of the picture, just behind where the letters '4KLU' are printed on the generator frame.

The four suspension springs are adjustable. In this organ, the springs at one end were too low, and the generator was dragging on the shelf. This would result in unwanted noise from vibration of the motor, and any oil put in would run to one end only.

Obviously, the organ itself must be perfectly level before adjusting these springs.

Motor and scanner assembly

2009-08-09T23:37:00.002+01:00

This shows the left side of the generator as viewed from the back of the organ. The large circular can at the left is the vibrato scanner.

The synchronous motor is immediately next to this, a rectangular block with black numbers printed on the side. On top of this is a small tray containing a felt pad. This is supposed to contain oil to lubricate the motor bearing and the scanner. It is totally dry, and clearly no oil has been anywhere near this for years.

After the motor there is a flywheel and a spring assembly, which is there to smooth out the rotation of the motor. A direct connection to the motor would not be completely smooth, and the 'pulses' created as it turns would end up in the sound from the generator.

In front there is a metal box for various electrical connections. Further along, the edge of the generator can be seen. The rods sticking out are the ends of the pickups, one for each tonewheel. These are magnetic rods with a coil of wire around them.

The Tonewheel Generator

2009-08-09T23:19:00.003+01:00

The sound on these older Hammond organs is created by a series of mechanical revolving tonewheels and magnetic pickups. This complex mechanism requires oil, as the label here shows.

Unfortunately, this particular organ hasn't seen any oil for years. Possibly decades. The whole thing is noisy when running and the high B tonewheel is not working properly. There is sound, but it is not even close to being correct.

Here the cover has been removed. This end has the main synchronous motor and the vibrato scanner.

The red objects on the top of the generator assembly are capacitors. Generally the red ones are more desirable than the alternative brown/yellow paper and wax ones. The older paper types dry out and the values can change dramatically, seriously affecting the sound.

Some people suggest replacing all the capacitors regardless of age or type, but this is not as simple as just buying new ones and soldering them in. Even small variations in the values will cause significant changes to the sound.

This is the other end of the generator, where the starting motor is located. The main motor does not start on it's own, and must be spun up to speed before power is applied.

This organ has a useless modification fitted. Someone has added a metal rod with a wooden block on the end. Presumably this was used to move the starting motor gear into position.

This is completely pointless. The starting motor includes a spring gear for this purpose. This evidently became sticky at some point, so adding some oil there woudl have solved the problem. Instead, someone went to the significant bother of adding this dubious modification.

Age Determination

2009-08-08T20:52:00.003+01:00

The age is best determined from the internal components. While this organ has a label inside with a date on it, everything else suggests this is wrong.

Speakers

These have 6 digit codes. The 575 is the manufacturer code (Heppner) and the other digits are the year (5) and the week number.

575546 Heppner, 19_5, week 46

575544 Heppner, 19_5, week 44

575546 Heppner, 19_5, week 46

Although no decade is specified, it must be the 1960's as the M100s were all made in that decade. The speakers therefore date from November 1965.

Capacitors

Two of these have the same code, 6516. Likely to be week 16 of 1965, which is April.

The other one is 24065. 65 again probably 1965, and the 240 could be the manufacturer Micomold.

Transformers

This organ has 2 amps, therefore 4 transformers. As with the speakers, the codes contain the manufacturer, year and week.

606526 Woodward-Schumacher, week 26, 19_5 (Black, main amp)

524 65 41 Triwec Transformer, week 41, 1965 (Silver, main amp)

606524 Woodward-Schumacher, week 24, 19_5 (Black, reverb amp)

524 65 33 Triwec Transformer, week 33, 1965 (Silver, reverb amp)

These weeks are in June / August / October 1965.

Valves

Or 'tubes' for USA types. The codes have worn off most of these, but the readable ones are 65-30, 65-35 and 65-44. Dates therefore are July / August / November 1965.

Paper Label

The date as written is 7/1/65. However this must be wrong, it can't be 1965.

7 Jan 1965 - No. This was before all of the components were made.

1 Jul 1965 - No. Still well before most of the components were made

7 Jan 1966 - Possible. Perhaps the person wrote 65 in error as only just into 1966?

1 Jul 1966 - Unlikely, as no components are dated 1966, and who makes an error with the year after writing it for over 6 months?

The Spring Reverb unit has 1122-6547. Unknown what the 1122 is for, but seems likely that 6547 is week 47 of 1965. This would be November 1965.

From this information, the likely assembly date of the organ is December 1965, assuming the speakers were the latest components fitted. The label is probably January 1966, with the person writing 1965 in error, as this was only a few days into the new year.

Probably finally tested in early January 1966 when shipped.

What's Inside - Part 2

2009-08-08T17:26:00.006+01:00

More pictures of the inside of the organ. Here is the vibrato line box, which connects to the motorised vibrato scanner. The red objects are capacitors.

This is just a phase shifter or delay line, which varies the pitch at each output. The scanner selects the various outputs in sequence depending on the settings selected.

This is the main amplifier, and the reverb speaker can be seen behind it. This is a valve (or 'tube') amplifier, no rubbish transistors or other electronic stuff here.

The mains lead (or 'power cord' if you are American) is soldered to two terminals directly behind the small metal box on the left.

The valves are the tubular glass objects, also here are the two transformers (black and silver cubes) and two capacitors (tall black and silver cans)

This is a closeup of the paper label tied to the wiring. Probably from when the organ was manufactured, it has the model and serial numbers at the top.

The middle section is for test results, most of which are not filled in.

At the bottom is the name 'Terry' whoever he was.

The date is 7/1/65.

The date could be read as 7 January, or 1 July. Either way, it must be wrong, since most of the components in the organ have date codes near the end of 1965. There is no way it was made in January or July 1965.

At the bottom right is the reverb unit. This is a very simple device, consisting of an output coil at one end and a pickup at the other. Two springs are stretched between them.

When a signal is sent into the unit, the springs vibrate, and continue to do so for a short while afterwards. The resulting sound is collected by the pickup and routed to the reverb amplifier, which is visible behind the spring unit.

The two main speakers can be seen in the background.

What's Inside - Part 1

2009-08-08T17:12:00.003+01:00

With the back removed, the internal components can be seen. At the top, the rear of the manuals (keyboards) wiring, and in the centre the vibrato line box.

The middle covered section contains the tonewheel generator.

The lower section contains the main amplifier (left), the spring reverb unit (right) and behind the spring reverb is the reverb amplifier.

The back of the three speakers can be seen in the lower section, the two large main speakers and the smaller 8 inch reverb speaker on the left.

I have replaced the mains lead (bottom left corner), since the old one was cracked and dangerous. This is not particularly difficult but does involve soldering the wires. Don't attempt this yourself unless you are practiced at soldering and understand the dangers involved with mains wiring. These organs contain mains voltages, easily enough to kill you. They can also store a significant charge for hours or days after being switched off, so don't go poking around in there unless you know what you are doing.

The Hammond Organ

2009-08-08T16:22:00.004+01:00

This Hammond M102 was found on eBay, and is in almost working condition. One of the tonewheels is partially jammed, no doubt due to lack of oil. Everything else is working.

The cabinet is good, there are only a few marks on the sides and top. The front edge is worn as would be expected.

The M100 series were all the same internally, the last 2 digits just denote the style of cabinet.
This is an M102, so has a contemporary style walnut cabinet. Serial number is 60759.