A Google search on <auto radio "motor generator"> returns a fair number of
references to motor generators used for B supply in early auto radios. I
think Carter Genemotor Corp. may have been a supplier. There are also
references to early radios using their own batteries and the vibrator power
supplies. I still do not recall exactly where I first heard about that use
of the motor generator.
An article in RadioCraft in 1934 intimates that there MAY have been
motor-generator recievers built, but provides no examples.
" The auto radio of a few years ago was a crude affair, in comparison
with present models. Whereas the old model consisted of numerous boxes
to hold the receiver chassis, speaker and "B" batteries, and the tubes
were such that very little amplification of the meager signal
(generally obtained from most auto antennas) fed to them was derived;
the new sets are practically just the opposite in that every
imperfection has been eliminated. The latest in auto-radio receivers
is a single unit with just one or two bolts, at the most, necessary to
anchor it to the car. Today "B" batteries have been done away with, a
"B" supply unit that obtains its power from the car battery being
employed to furnish the necessary plate voltages. This unit may be
either of the motor-generator type, or a vibrator which chops the 6 V.
D.C. (from the storage battery) into pulsating D.C., stepped up by a
transformer to approximately 225 V., A.C. and then rectified and
filtered by a special rectifying tube and filter arrangement. Some
receivers employ a mechanical rectifier, operated "in step" with the
vibrator "chopper," to eliminate the necessity for an extra tube. "
There is also reference made to a 6 tube motor-generator set along
with 110 volt DC sets, not in an automotive context. 110VDC radios
would have been used on an edison system - and since DC cannot be
transformed an M/G set would be required to produce voltages other
In 1926, W.M. Heina got a patent for the Heinaphone - a "travel
radio" which could be installed in a car and used both "A" (1.5 to 2
volt) and "B" -(90-120 volt) batteries. These radios could not be used
with the engine running.
The first radios that could be used with the engine running came in
1927 with what was known as "damp resistance".
In 1932 "B" battery eliminators using both vibrators and
motor/generators became available for use with older sets. No mention
made of a dedicated auto radio with a motor/generator.
In a National Radio Institute publication ( #32 - How to Service Auto
Recievers) of the time it states "police cars and other special
applications sometimes used small motor-generators instead but these
are rarely found in private cars" It appears to be produced about
I also found a vague reference to an aftermarket radio for a '32 ford
- Motorla 300 - that MAY have had a motor-genreator power supply as
one of the three parts. However, since Motorola was definitely using
vibrator power supplies on earlier radios, I doubt they actually used
an M/G on this radio.
That's allI found googling "AUTO RADIO" AND "GENERATOR" OR "MOTOR" OR
my 49 Packard Hearse had a motor generator to run the radio. Took about
30 seconds from the time you turned it on, to when the sound started
come on. But there was a "whirling" sound the instand you turned it on
I had a 10 meter military radio mounted in it that would receive the
local police department (circa 1970) with multiple pushbuttons for
channels. I think its still in my dads place along with my RTTY gear.
It had a big MG on it.
"Not so old as to need virgins to excite him,
nor old enough to have the patience to teach one."
You gotta admit, gunner, that radio was NOT an automotive radio. It
was a "10 meter military radio"
As for the 30 seconds before sound, with a whir from the getgo - it
took about 30 seconds to warm up the tubes, and the 115cps vibrator
started as soon as the switch was turned on. MG power supplies kinda
"wound up" from an initial "growl" to a high pitched whine or howl
usually with lots of overtones. The vibrator started up immediately
and held a constant frequency from startup to shutdown. An MG "wound
down" when the switch was shut off.
MANY tube radios of that era did; I used to fix them.
But not even the antiques the boss's customers owned had dynamotors
for receiver supply; just transmit. Some were vibrator RX supply,
others transistor-driven invertor.
I strongly doubt dynamotor use for receivers, two way or broadcast, was
common at all.
a) Dynamotors have a limited lifetime. A police car might get maybe
10-15 minutes of transmit time per day; but 24 hours of receive time if
all 3 shifts use the car.
b) Dynamotors draw LOTS of current. Your average 1960 MOPAR had a ~30
Amp generator; it made zero amps at idle and its rated power at good
speed. It wasn't AC that had cops always idling the car. There were
fast-idle solonoids [ie mash the mike button and the engine sped up...]
We used to suggest 100A Leece-Neville alternators, originally with
the selenium rectifier stack on the firewall, for many customers.
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I cannot say they were common, but as a kid I had a Ray Jefferson marine
radio that had two dynamotors; one for transmit and one for receive. Key
the microphone and it went from noisy to really noisy.
Well unless you can document it, I'm not believing it, from my
research. ALL dedicated automobile recievers I have been able to track
down from that period used multi-vibrator power supplies - and wuite a
few of them were syncronous, meaning no rectifier was required - just
a good filter cap bank. The only M/G power supplies I have been able
to document, and/or have seen, was for 2 way radio apps. (police
radio, aircraft, military, HAM, etc)
A few more references found by Googling <auto radio dynamotor> including an
article in July 1932 Popular Science on page 63. Probably about a dozen
total references found referring to dynamotor (motor generator) power supply
for early automobile broadcast receivers.
Thanks for the link, Don.
It indicates, as I suspected, that the very few dynamotor auto radios
were battery sets with an optional dynamotor. The only one sold with
the dynamotor as "standard" was the Grisby-Grunow built "Majestic
Model B" for the 1932 Ford V8 - and it was their battery set provided
with an AE (Automotive Electric) Dynamotor battery eliminator as
Packard Electric supplied an optional dynamotor for use on Packard
cars also as a one year? option.
The 1932 Boasch 920 was also a battery set with an OPTIONAL dynamotor
battery eliminator called the Magmotor.
It appears the dynamotors were not available before 1932, and were
virtually dead by 1933 due to the superiority and lower cost of the
By 1934 car radios had started to resemble those we are familiar
with, with the high voltage supplies totally integrated into the radio
set. One peice radios with integrated speakers were very common, and
"remote head" radios were available to fit the controls into tight
places and free up the glove box.(without mechanical drive cables as
A "battery eliminator" dynamotor needed supply only10- 20ma at 90-180
vdc, (about 3.6 watts MAXIMUM) and drew in the neighbourhood of 6 amps
from the 6 volt battery (36 watts) for a 10% efficiency - on a GOOD
model. Many were even more dismal in performance, while a syncronous
vibrator was well over 65% efficient.Dynamotors were also relatively
shortlived - wearing out brushes and bearings quite quickly while
vibrators lasted for many years without service or repair.
I'm interested - please post the link.
I found a link to an article by automotive writer Michael Lamm on
American Heritage.com that references dynamotors but does not give an
example of a single actual model that used them. Most of the reference
seams to be to those radios that did not work with the engine running.
I wouldn't call it a technical reference nor would I accept it,
necessarily as fact.
ALL the information I have had access to indicates radios prior to
1931 or the introduction of the "motorola" were battery sets - most of
them adaptations of domestic recievers. Aftermarket "battery
eliminators" of 3 types became common to replace those batteries
somewhere around the same time. These were "interuptor vibratror",
Syncronous vibrator" and "dynamotor" types.
There is no record that I have been able to uncover of an automotive
specific radio reciever for general broadcast use that came from its
manufacturer with a dynamotor type power supply. Particularly none
that were capable of being used successfully with the car in motion.
If someone can find a specific reference to a specific model, with
believable specs showing it came with a dynamotor supply, I'm all
Antique cars and antique radios have both been hobbies of mine over
I couldn't figure out how to post a link to the Popular Science article. I
found it thru Google Books. I don't think it specifically says that a radio
was supplied by the manufacturer as a package with a dynamotor, only that
they were used that way.
The old Rider, Supreme, or similar service manuals might provide more
I think I've got the link. you may have to scroll to find page 63 or 64. The
article seems to treat the dynamotor as a battery replacement, not original
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