The first small commercial returns are now coming in. As 1952 ended, the transistor made its debut in a commercial product - the Sonotone hearing aid. Sonotone announced that in its new $229.50 instrument, one of three vacuum tubes had been replaced by a transistor (made by Germanium Products), permitting "double the power at half the operating cost."
Above on the left is a Sonotone 1010 on the right a Sonotone 1111. They are distinguishable externally only by their unique grill designs. Both shared the same basic case (3" tall, 1 1/2" wide, and 5/8" deep) and circuit board dimensions. The later Sonotone model 200, also discussed below, was another member of this series.
SONOTONE MODEL 1010 (Ten Ten) HEARING AID. This was the first Sonotone
design (or any commercial design for that matter) to utilize a transistor.
It was introduced late in 1952 and as mentioned above, cost $229.50. This
was a staggering amount in those days and would be equivalent to about
$1450.00 today. The 1010 was a hybrid device consisting of two sub miniature
pre-amplifier tubes and a single transistor (visible on the right side
just above the tube sockets) as the final audio amplifier. The reason for
such a design was that the first junction transistors had signal to noise
ratios which were inferior to tubes. To overcome this limitation yet benefit
from the low power consumption of transistors, the hybrid design was developed.
Within months, however, manufacturers had refined transistor production
techniques, thus largely eliminating noise as a design factor. At that
point (late 1953) the low power consumption of transistors combined with
their decreasing cost, effectively killed the vacuum tube as a viable alternative.
For this reason the hybrid 1010 had a relatively short product life cycle
and the a total production of only a few tens of thousands. Because of
this they are rather scarce today and a very desirable addition to any
transistor related collection.
An example of a hearing aid using a combination of tubes and transistors (Sonotone "1010") is shown in block diagram form in Fig. 1. For the tubes, this instrument uses a 15-volt B battery with a life estimated at 2,000 hours at a drain of 60 microamperes. A 1.25-volt A battery powers the transistor and heats the tube filaments. Life of the A battery is 63 hours at an average current drain of 13 milliamperes.
In this unit a special transformer was required to match the high plate impedance of the driver tube to the low base-input impedance of the transistor. A primary impedance of over a half megohm is achieved by winding 10,000 turns of No. 48 wire (657 feet, at 1.8-thousandth-inch diameter) on a core built up of subminiature mu-metal laminations. Special techniques are, of course, required to form this winding without breaking the fine wire used. The 250-ohm secondary consists of 200 turns of No. 45 wire. A tantalytic capacitor is used in the circuit of the brute-force filter in the constant-current source for the base circuit of the
transistor. Available power output of this tube-transistor instrument is 13 mw, which provides 124 db of sound pressure in the ear. The acoustic gain is 65 db, and residual noise level is at least 50 db below maximum output at full-gain setting. The transistor used is an npn junction unit manufactured by Germanium Products Corp. of Jersey City, N. J.
Above is a better view of the transistor with the tubes removed from their sockets. As noted above and based on the observations of my collecting friends, the earliest 1010's had a Germanium Products TN-10 NPN junction transistor which was encased in a black epoxy filled plastic shell. These are very rare. The large round silver device is a tantalum electrolytic capacitor which has a date code of 6-53 (June, 1953). Observation suggests that the first digit of the Sonotone serial numbers is the model of hearing aid, hence the "3" in s/n 320486 represents a model 1010 and is perhaps the 20,486th unit to be built.
My 1010 has a TI type 203 NPN grown junction transistor in the typical TI standard oval shaped hermetically sealed case. Other 1010's have been found with transistors made by Raytheon. There may have been other manufacturers as well. It is interesting to note that the Raytheon is a CK718 (a PNP design) and as such, would have required some circuit modifications to function correctly.
The reason for my 1010 having a TI transistor may be suggested by the date code which is 616 (16th week of 1956). This indicates that it is not the original transistor and was probably installed later as replacement part by a service technician. Supporting this conclusion is the fact that the leads are covered with a brown plastic insulation rather than the clear insulation which is common to virgin examples of 1010's and 1111's.
The 1010's tubes are among the tiniest I have ever seen. The picture above compares them to a TI transistor similar to the one in my 1010. The tubes may have been manufactured by Sonotone, but have absolutely no markings and a round five pin configuration. Raytheon used "flattened" design in which the five tube leads were brought out in a line similar to transistors of that time. (See my Zenith Royal-T pages for a picture of the Raytheon style of subminiature tube)
It must be noted from a historical perspective that just because the transistor actually found its way into hearing aids, its widely proclaimed advantages were not accepted without question by skeptics. Transistors were a major new technological step forward and not at all embraced by everyone. This probably limited initial sales to wealthier purchasers who were not afraid to be early adopters. To give a sense of what the general public was learning about these new devices here is a rather harsh news assessment from the July, 1953 Consumer's Research Bulletin:
HEARING AIDS with a new electronic amplifying device called a transistor have appeared on the market. The transistor may be used without tubes or in various combinations with tubes. The object is to provide economy in the use of batteries. At the present stage of development, the transistor is considered unsatisfactory. Apparently the difficulty is due to moisture, and the hearing aid goes bad due to early failure of the transistor. Until more development work is done, hearing aid wearers who do not wish to act as guinea pigs will, we believe, do well not to spend their money on transistor type aids.This report was referring to the fact that many first generation transistors were not hermetically sealed and moisture encroachment was a real problem over time. A follow up news item appeared in the December, 1953 Consumer's Research Bulletin:
THE NEW TRANSISTOR HEARING AID is still at an unperfected stage, although it is being advertised as a new scientific marvel. The Council on Physical Medicine and Rehabilitation of the American Medical Association reports that at the present time the most important advantage that can be claimed for the new development is an appreciable reduction in the operational cost, as much as 80 percent. The Council notes that there does not seem to be any significant improvement in amplification, in tone quality, or in fidelity of the transistor aids over aids of other types and advises the purchaser to obtain a written guarantee to cover possible mechanical and electrical defects in a new instrument.Despite the conservative position of Consumer's Bulletin, sales of transistorized hearing aids rapidly increased while the power hungry tube models died out just as quickly.
Here is a second 1010, s/n 313927, which is also in my collection. This unit was slightly earlier in production than the HA described above and it contains a Raytheon CK718 PNP transistor dated 317 or the 17th week of 1953. This corresponds to late April or early May.
The clear plastic insulation on its leads indicates that it is a
factory original. It is also interesting to note that the transistor has
a "serial number", 1331, hand painted on its side. Supporting the early
1953 manufacturing date is another "mushroom cap" electrolytic capacitor
which is dated 4-53 or April, 1953.
I was able to acquire a third 1010, s/n 303320, for my collection. This is a very early production unit and has a tantalum capacitor dated 1-53 or January, 1953. Unfortunately the original transistor had been replaced, probably by Sonotone as a repair "upgrade". The replacement transistor was very small and although there is no identifiable type stamp, it is marked "TI" on one side. Comparison with other comparable examples appears to confirm that it is a Texas Instruments product. Given the low serial number of this 1010 I decided it would be appropriate to cosmetically restore the hearing aid by replacing the TI transistor with an equivalent to the probable original GPC device.
Shown above left is the restored 1010 with the "as found" replacement TI transistor below it. It was wrapped in the typical Sonotone red insulating tape on the left. I was able to obtain a suitable GPC device which I carefully installed. The result is comparable in appearance to original 1010 photographs I have seen. Shown on the right is a rare original GPC TN10 transistor which was found by a fellow collector in another 1010.
It appears to me that not many 1010's managed to survive without undergoing a factory "upgrade" at some point during their working lives. This is unfortunate since it makes it difficult for collectors to obtain a correct example of this historic product.
My tongue in cheek observation is that the Sonotone 1111 is like a box of CrackerJack candy because you never know what kind of prize will be inside!
Here is an inside view of the Sonotone 1111. The circuitry is hand wired and appears to be the typical three stage transformer coupled design. Three soldered germanium junction type transistors are utilized. From a collectors standpoint soldering is a plus since it prevented service technicians from easily "upgrading" the original transistors, which seems to have been a common practice with socketed products such as the Zenith Royals. This unit has two Texas Instruments devices, a type 204 dated 413, and a type 205 dated 403. Both clearly have the TI logo stamped on one side. Another curiosity with the TI's is that the 204 has a yellow paint dot next to its emitter while the 205 has a yellow paint dot next to its collector. The final transistor is a rarity labeled TN-29 on one side and RDR 1 on the other. Research has confirmed that it was made by Germanium Products Corporation, a subsidiary of RDR (Radio Development & Research Corporation). As an side note... the "TN" prefix on Germanium Products transistors equates as follows: T = transistor and N = npn. GP also had a corresponding "TP" series: T = transistor and P = pnp.
Another view of the Sonotone 1111 chassis showing the transistors, which were all wrapped in red electrical tape for some reason. Clear plastic insulation was also placed on all the transistor leads to eliminate short circuits. The microphone has a code of 425 stamped on it. This may be another clue as to the date of manufacture. The serial number is 418465. Information compiled by fellow collectors tends to support the conclusion that serial numbers for 1111's begin with the digit 4 and continue sequentially from 1954 through at least 1956. Thus this unit is probably the 18465th unit made.
Here is a closeup of the Sonotone 1111's transistors. The adhesive left behind by the red tape is visible. The two end units are Texas Instruments and the middle unit has markings with characteristics linking it to Germanium Products Corporation, one of the very first transistor manufacturers.
Above on the left is a second 1111 which I was able to acquire. The serial number is 437874 and was thus made later than the previous example, probably the 37874th unit made. A close look at the lower right hand corner shows that it has three unique types of transistors (Raytheon, RCA, and Philco). Next to it on the right is a Sonotone model 200 from 1961 which obviously shares the same basic chassis. I have included it here to illustrate the dramatic decrease in transistor size which occurred in just a few short years. The 200 has four tiny silver colored Raytheon CK897 transistors. Three are below the volume control and one is directly above the yellow tape on the left side.
Above is a detailed look at the transistors in the second 1111. Included are a Raytheon CK718 dated 434, an RCA 2N77 (also labeled TP56), and finally a Philco unit whose markings cannot be read but is probably a 2N48 which was used in similar products of that era.
Finally, here is a close look at one of the tiniest Raytheon transistors you will ever see. That's a standard 1/4 watt resistor on the left! It is a CK897 from the 1961 Sonotone model 200.
SONOTONE 1111 DATABASE. Since I originally wrote this article I have acquired a few more 1111's. I am presenting their basic information sequentially (including the ones pictured above) in the interest of better understanding the production sequence and various component types.
S/N 400544: CBS Hytron
J-10 (DC = 334), Raytheon CK718 (DC = 418), and Raytheon CK718 (DC = 430)
S/N 418465: GPC TN-29
(DC = ???), TI 204 (DC = 413), and TI 205 (DC = 403)
S/N 433909: TI 203 (DC
= 434), TI 204 (DC = 421), and TI 205 (DC = 421)
S/N 437874: PHILCO 2N48
(DC = ????), RCA 2N77 (DC = ??), and Raytheon CK718 (DC = 434)
S/N 450753: PHILCO TP-47
(DC = 5622), RCA 2N105 (DC = 6C), and RCA 2N105 (DC = 6C)
In conclusion, the Sonotone 1010, 1111, and all their cousins are
milestone transistor products and desirable collectible items in their
own right.
