Door Chime Mechanisms

I think the attraction for me about door chimes is that they are perhaps the first piece of electro-mechanical automation that was available to average people for their homes.   Just the idea of pushing a button and having some solenoids do a little job for you is entertaining.

In simpler one or two tone chimes, the instant the door bell button is pushed, the solenoid is activated via a direct path circuit and the bell sounds right away.  The electrical path is a bit more complex in a 4-tone chime.  As described above, the power needs to be sequenced through the distributor.  When the door bell button is pushed, that turns on power to the motor that drives the distributor, the commutator starts moving, and only once the commutator touches the first contact does the chime sequence start.  In models with a rotary distributor, the door bell button has to be pressed and held momentarily in order for the commutator to overcome the start resistance in the distributor assembly.  All of this is entirely normal, but might seem odd to those familiar with the immediate action of simpler chimes.  The start resistance in the distributor can cause a problem though.  In some models the start resistance can be adjusted. Too much resistance and the distributor will not start.  Too little resistance and the distributor will not stop and the chime sequence will replay indefinitely.

Some older mechanisms have a number of natural rubber parts in the unit assembly.  Each subassembly is attached with rubber grommets, presumably to deaden any vibration or mechanical noise that could detract from tone quality.  In addition, the caps that retain the plungers and springs inside the solenoid cylinders are often made of the same natural rubber material.  Natural rubber has the nasty habit of drying out and turning brittle or crumbly as it ages—and forty or fifty years is beyond its life expectancy.  As a result, these older mechanisms are in need of refreshed rubber.  Rubber grommets and neoprene washers are readily available at any well stocked hardware store, so getting replacements for these parts is no problem.  Doing the R&R on the grommets is time consuming but not especially difficult.

The solenoid caps however represent a different sort of problem.  I recently found one vintage mechanism that was missing the plungers and springs.  At first I thought the unit had been scavenged for parts, but after more thought, arrived at the theory that once the caps had become adequately decrepit, the plungers broke the caps away on the rebound stroke and were lost forever.  Whether or not it happened that way, the problem remains certain that the ancient rubber caps fail.  This really complicates the solenoid cleaning process described above —if removed, the caps will crumble and need to be replaced.   Oh yeah--- and if the rubber washers and caps parts have decayed, there is a really good chance that the insulation on the wiring has also gone the same route.     

Here’s a quick survey of some of the common mechanisms and generally how they work:

A -B-C  First generation Nutone 4-note.   I don’t know dates for certain, but 1936-1940 seems likely. The mechanism is really odd.  One dedicated solenoid has the task of pushing the commutator upwards  very quickly and then a combination of gears, springs and gravity draw the commutator slowly down and across the contacts. It makes lots of mechanical noise which I think adds to its vintage charm.  This one  can be quite a handful to repair. It is prone to not just the typical solenoid plunger problems, but also the clockworks mechanism is sensitive and very likely to need a thorough cleaning.  Plus, all those wires between the sequencer and solenoids have to flex every time the mechanism box is opened and closed, so wire damage is entirely possible.   This is a classic example of the sort of design that preceded the "new and improved" model, but once sorted out, it should be dependable. .

D  First Generation NuTone 8-note.  Again, this one likely dates from 1936-1940 and is contemporary of the 4-note, but offered as the most deluxe model in the early NuTone line. It uses the same metal housing, but instead of the solenoid powered commutator, it has a motor driven rotary distributor, hence the term “motored”. This is the general scheme that would be followed by all future 8-note NuTones and many competitors’ models.  On this early one, the distributor is very much exposed, the synch motor is inside.  The socket in the center is for a light bulb that serves the night light function, controlled by the pull switch on the left.

E  Second Generation NuTone 4-8 Note. This is the classic NuTone machine, believed to be introduced in 1940, and made in its essential form through the late 1990’s.  The distributor “synchronous” motor is visible at front left, while the guts of the distributor are under cover accessible at the rear.  The socket at top center powered either a clock or a light bulb, depending on model. These are about as robust and trouble free as they come.  Typical problems are dirty solenoids and rotten rubber parts, and occasionally a minor adjustment to the distributor.  In my view, the high water mark for multi-note NuTone chimes.  Previous models were quirky and sensitive, later models were basically cost reduced versions of this one.

F  This ingenious device was an addition to the NuTone second generation in the late 1950's which allowed for a secondary door to ring two notes (while a third door can ring one note in typical fashion).  The way it works is that a pivoting tab on the back of the plunger activates a reed switch as it passes it.  The tab folds down on the outward  power stroke so as not to activate the switch. On the rebound stroke the tab stands up, momentarily closing the switch and energizing solenoid #4 for the second tone.  Shown here with cover and integrated backstop removed in order to see the workings. 

G  I call this the third generation for NuTone.  The configuration is very similar to the previous model, but a circuit board replaces some of the discreet wiring, the synch motor is rated at 16v and the bell hangers are vertical blades. I am guessing that this one dates for the mid 1970’s.

H  Edwards—very similar in concept to the first generation NuTone 8-Note, but much more highly evolved and very robust. This one dates from the early 1950's. The only oddity is that this one like some other Edwards motored chimes cannot be used with a lighted doorbell button.  The light in the button allows a trickle of power through the circuit that will cause the motor to run non-stop.

I   The start resistance adjustment on this model is easy to make:  loosen the set screw on the commutator and slide it in or out just a bit on its shaft.  It's sensitive though, so It may take a few tries to get it just right.

J  Early Rittenhouse— Used in model 610, 410 and others.  It is by far the most difficult to fix mechanism I have found.  The core of it is the unique sealed sequencer, referred to as a "dashpot".   Its all hidden inside the aluminum can, which is permanently sealed to contain an oil bath. It was never intended to be serviced.

K  Here's what's inside the dashpot.  The theory is something like the earliest NuTone 4-notes:  a solenoid quickly pushes a commutator downward, which then is pushed upward by a spring and swipes four contacts.  The plunger's return motion is retarded by oil metered through an adjustable port that counteracts the push of the return spring. It is an interesting piece of engineering, but ultimately too dependant on a delicate balance of spring compression and torsion, friction, lubrication, gravity, hydraulic resistance and your personal karma.  It is no wonder that this was a genetic dead-end for door chime evolution.

Many of these are still in service and working fine.  When they fail, they fade slowly.  If yours has the typical problems of running really slow, or not playing the last note, or getting stuck on a note leaving the solenoid powered and buzzing  you may have luck by simply adding oil.  Scrape off the top seal around the fill screw on the top, remove the screw and top up the can with light oil.  Beyond that simple operation, the can must be surgically opened for additional service. After opening it up, I had luck by shimming the return spring to compensate for its tiredness, cleaning everything really well and also drilled an additional oil port.  Then the sequencer  needs to be put back into the can and the assembly sealed with epoxy.

Ultimately a better repair strategy may be to find some modern electronic component to replace this sequencer.  Anybody have any ideas?

L  This is another dashpot design. It is essentially the same in concept, but crudely constructed by comparison.  No brand marks on the chime it came from, so its just a guess as to whether it is a cost-reduced variation by Rittenhouse, a licensee of their patent, or just a knockoff. This one is packaged inside a plastic housing, orderly enough on the outside...

M  ... frightening on the inside.  The oil had the look and consistency of molasses, but smelled much less pleasant and had turned chunky at the bottom, like the dregs in the bottom of a tired crankcase.  No sign of this one ever having been used-- it died of atrophy.

N  Mostly the same parts onside, but simpler in all regards.  Check valve for  the inflow of retarding fluid is at the far left, solenoid coil in the center, solenoid plunger and spring on the right.  The feeler sequentially touches the four contacts sending current to the solenoids.

O  Aside from the questionable dashpot designs, Rittenhouse made some excellent chimes, like this one from 1939. Also using the same general configuration as the first generation motored Nutone, and like the Edwards, the distributor is up front under a removable cover. The unusual diagonal solenoids must have been arranged that way to make for the most compact assembly, depth wise. I have also seen a variation of this one with three solenoids-- one of the few 3-bell chimes that actually uses the third bell.  The only unusual service issue with this one is that the motor runs in an oil bath and may need to be oiled on occasion.  There is a fill port accessible by a screw  on the top of the motor housing.  There is an overfill outlet  port on the left side of the motor housing (at 9 o'clock facing front); don't overfill or you will have a dripping oil mess to clean up. Also, when positioning  the left-most bell, be sure that it doesn't contact the #3 solenoid coil, which is extremely close.  It won't cause any damage, but just being in contact will damp the tone of the #4 bell.

P Q Later Rittenhouse chimes continued the same general theme, though had a more finished look about them, like this handsome 620R model. Like the later NuTones, the need for adjustment seems to have been engineered out.  This seems like a very robust design. The one that I have looked like it had a tough life, but still worked perfectly with no repair required, just some very  minor adjustment.   Note the unusual staggered placement of contacts on the distributor plate.  It plays a sequence of  3 notes, 2 notes, 2 notes.  The unusual fifth solenoid is a two-way dedicated to provide a 2-note chime for alt door #1... effective but oh so less elegant than the NuTone solution.

R  In the early days, chime makers were on a mission to find novel ways to cost reduce chimes while maintaining or even adding function.  This Edwards from the  1940's is a classic example.  While the obvious way to get four notes plus two notes for an additional door would be to have four 1-way solenoids to play the 4-note sequence, plus an additional 2-way solenoid to do the ding-dong thing.  This one does that job with just two 1-way solenoids plus one 2-way solenoid. In the four note sequence, the two 1-way solenoids strike the first two notes, then the 2-way solenoid strikes the third note and remains energized for an extended period, then released to strike the fourth note on the rebound stroke.  

S  Here's a  wacky design if ever there was one- the Rittenhouse "Controlatone" mechanism.  The mystery component  located between the two solenoids is a thermal cutout switch.  It functions to shunt power from solenoid 1 to solenoid 2.  It's hard to imagine a weirder or more complicated way to get two notes.  Especially odd to figure considering that Rittenhouse was making a much simpler 2-note design of the the typical configuration at the same time and this seems to have no apparent benefit for the added cost and complexity. Reading the text of the patent for this one explains the thinking.  The thermal switch effectively worked as a timer to time the delay of the  "dong" after the "ding".  It also served to enforce a brief time-out before the chime could be struck again.  From the department of Answers to Questions That Were Never Asked! 

T  Edwards two note mechanism in production from the early 1940's through the 1950's is typical of most simple ding-dong chimes.   There are two solenoids.  One is a 2-way that strikes one bell and holds it until power is released, then pushed by a spring and strikes the other bell on the rebound.  Generally this two-tone solenoid is connected to the front door bell circuit.  The other solenoid is identical but is restrained from hitting the second bell by  a stop. You can clearly see the stop to the left of the upper solenoid. This solenoid is generally connected to the side or back door.

U  The casual observer would assume that 3-bells means 3 notes, but that is not generally the case.  Most 3-bells, like this 1957 NuTone L33 are simple ding-dong 2-note chimes.  The center bell is just for looks. The couple who sent me this picture were having a "discussion" about why the chime wasn't ringing all 3 bells. Hey-- I didn't know either until I saw this picture.  This one is noteworthy for another reason.  It's a bit of an oddball in that it has what I describe as one and a half solenoids.  The 2-way solenoid has one tube, one plunger, two internal springs and two coils. One coil is energized for the 2-note front signal; the other coil is energized for the 1-note back door signal.  I suppose this was an effort at cost reduction over the more typical- and logical- twin solenoid design.  It worked only moderately well and was discontinued in future models.

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