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.
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
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:
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
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
ingenious device was an addition to the NuTone second
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
here with cover and integrated backstop removed in order to see the
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.
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
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
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.
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
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?
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
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.
from the questionable dashpot designs, Rittenhouse made some excellent chimes,
like this one from 1939.
using the same general configuration as the first generation motored Nutone, and like the Edwards, the
distributor is up front under a removable cover.
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
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
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.
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.
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!
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.
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
"door chimes" above to see other related topics.
I am a
lot more skilled at fixing old door chimes than I am dealing with search
engine optimization, so here a a few terms and phrases that might help
surfers find me.
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