written by JR2WZQ / KOHNO Katsuyuki (published October 1, 2020)

e-mail: jr2wzq<at>yahoo.co.jp

Foreword

We, the home-manufacturing radio amateur, can easily mention 2SC1815 originally manufactured by Toshiba as the most standard transistor in Japan. Currently, however, only its market stock or equivalents manufactured by third parties are available, since the production by Toshiba had already ceased. Because the quality of equivalents manufactured by third parties including noise figure characteristics is reported to be almost the same to the original (Kato 2019), 2SC1815 will stay for a long time as the most standard transistor.

2SC1815 is used in the purpose for DC, AF, and RF application up to around 50 MHz. As we can easily pic up the name of 2SC945 (NEC), 2SC828 (Panasonic), 2SC536 (SANYO) and 2SC458 (Hitachi) as a similar general-purpose transistor to 2SC1815, it will be interesting to explore the reason why 2SC1815 could become to be the most standard product. As I have some documents about them, I would like to explore the history.

‘Data books’ and ‘Standards tables’

According to the progress of Internet, data books of electronic devices such as semiconductors in a booklet form provided by manufacturers became uncommon, and nowadays the datasheets of them are usually provided as electronic files. In the past, however, data books in a booklet style were provided by most manufacturers and were common. The data books in the past were not for the use of end users such as radio amateurs but for the use of developers of application products. Therefore the number of it generally circulating seemed having been scarce. I have data books that was removed from university libraries or purchased at a second-hand bookstore.

Apart from that, ‘Standards tables’ in a booklet style, in which principal part of many ‘Data books’, e.g., maximum ratings and major electric properties, had been published by CQ publishing Co. Ltd. (Tokyo, Japan) every year. Among them, ‘Standards tables’ [規格表] for discrete transistors as “The Newest transistor standards tables” [最新トランジスタ規格表] had been published every year from 1966. In 1988 edition or earlier of them, the data for all items of transistors were displayed in it; however, those of discontinued ones were not displayed in the later edition since 1989. For the amateur use, discontinued items are commonly used; therefore, it is strongly recommended to keep aside the 1988 edition, of which the data were also included in the CD-ROM having been provided as an appendix for the 2013/2014 edition.

Relationship between 2SC1815 and 2SC372 family

It seems that 2SC1815 has been firstly appeared in the data book published by Toshiba in 1976. Based on description in the data book published in 1976, 2SC1815 had been categorized by hFE into O, Y and GR, of which the principal electric characteristics shown as a table are as same as those of 2SC372-O, -Y and 2SC373, respectively. However, among of only Vcbo and Pc of 2SC1815 are higher or larger than those of 2SC372, which might imply that 2SC1815 was provided as an upward compatible successor product (Table 1). Therefore, before considering the 2SC1815, it will be necessary to mention the history of the 2SC372 family.

Appearing of 2SC372 family

2SC372 family, of which the appearance is peculiar silk-hat-like, was very popular among radio amateurs who manufacture radio equipments. One of the first transistors I used in my hobby of electronic manufacturing when I began it around 1972 was also 2SC372-O. Interestingly at that time, resin mold silicon transistors had peculiar appearance depending on manufacturers.

The characteristics of 2SC372 family (2SC370–374), a series of epitaxial-plainer-type silicon transistors, were probably at first appeared in “Toshiba Semiconductor Hand Book 3” published in 1966. The application of them described in the data book was assumed to be ‘RF amplification’ and ‘AF amplification’. Those of 2SC370G-373G, which are categorized as ‘Green Transistor for communications industry’ assumed to be used in ‘RF amplification’ and ‘high-speed switching’ application, and of 2SC361–363, which was assumed to be used for the application of ‘RF amplification’ and ‘AF amplification’ having similar characteristics to 2SC372 family but plainer-type, were also published in the same data book. 2SA495, which is later assumed to be a complementary pair to 2SC372 family, had not yet been appeared in the same data book.

We can find the advertisement by Toshiba in the back cover of “The Newest transistor standards tables” 4th edition published in 1967 that 2SC361–363 and 2SC370–374 assumed to be ‘general purpose’ and ‘AF and RF amplification’, respectively. However, only 2SC370–374 became popular and 2SC361–363 seemed to be soon discontinued without disseminating.

Historical transition of 2SC372 family

2SC361–363, and 2SC372 family when at first appeared, were categorized only by hFE but not within the same product number (Table 2). However, based on the description in “Toshiba Semiconductor Hand Book (1969 General edition)” published in 1968, 2SC361–363 had been discontinued and the hFE category of 2SC372 family became subcategorized within the same product number according to the hFE. According to that, there is entirely no difference between 2SC371-O and 2SC372-O.

Moreover, 2SC370T and 2SC371T, which are assumed to be used in ‘RF power amplification’ and ‘RF output amplification in 27 MHz citizen band’, are published in the same data book, in addition to 2SC370G-2SC373G. We cannot know the difference in the electrical characteristics between 2SC370T-371T and regular 2SC372 family because the characteristics of them displayed were tested in different conditions; however, VCBO among them of 2SC370T-371T is a little higher than that of the regular 2SC372 family.

Based on the description in “TOSHIBA SEMICONDUCTOR DATA BOOK (Transistors)” published in 1976, 2SC370, 371, and 374 among 2SC372 family had been maintaining/discontinued, and therefore only 2SC372-O, -Y, and 2SC373 (including 2SC372G-O, -Y, and 2SC373G) were left as current products at that time; in addition, 2SC1815 appeared in the data book for the first time. 2SA1015, which later became a complementary pair to 2SC1815, had not yet included in the data book; in contrast, 2SA495-O and -Y were included in it as a complementary pair to 2SC372. Based on the description in the data book, as already mentioned above, we can recognize that the electric characteristics of 2SC372 family and 2SC1815 are equivalent each other except that the packages, i.e. silk-hat-like packaged 2SC372 family and TO-92 packaged 2SC1815, and some maximum ratings are different. However, when we look at the outline drawing of 2SC1815 in the data book published in 1976 very carefully, the shape of the leads are different from that of newer 2SC1815, for example as that is indicated in the datasheet published in 2002. In addition, although it is impossible to be known only from published drawings, the direction of marking of the production name and the lot number is different between the older and the newer.

The appearance of 2SC1815 to the front stage and the retirement of 2SC372 family

Although 2SC1815 and 2SA1015 appeared for the first time in the 1978 edition of “The Newest transistor standards tables”, it was not in the tables of the main text but in the advertisement of Toshiba in the back cover of it. We could not see them in the tables of the main text until the publication of the 1979 edition. The maximum ratings exhibited in the 1979 edition were not same to that exhibited in the data book published in 1976 but same to that exhibited in the newest datasheet that we can obtain (Table 3, data in the 2002 edition are shown). Although we cannot exactly know the shape of the leads from the drawing exhibited in “The Newest transistor standards tables”, the shape of the leads is strongly suspected that they have been at that time already changed to the newer, because the maximum ratings of 2SC1815 exhibited in the 1979 edition had been changed to the newer. If so, the maximum ratings and the shape of leads of 2SC1815 had been altered within a relatively short period.

Although the maximum ratings and the shape of the leads of 2SC1815 had become newer by 1979, the maximum ratings and various electric characteristics of 2SC372 family, which were current variety at that time, exhibited in the 1979 edition were same to those exhibited in the data book published in 1976, and the package of 2SC372 family exhibited in the 1979 edition was silk-hat-like. The package and the maximum ratings of 2SC372 family exhibited in the 1981 edition, although I regrettably could not examine the 1980 edition, were changed to the same to those of 2SC1815, and were noted being maintaining/discontinued. It is also possible to know from the 1981 edition that the maximum ratings and package of 2SA495, the complementary pair of 2SC372, had been changed to those of 2SA1015, and noted being maintaining/discontinued. The official name of 2SC372, 373 and 2SA495 at that period are 2SC372TM, 373TM and 2SA495TM, respectively, although it is impossible to know those from “The Newest transistor standards tables”. Although it has been impossible to see the datasheets of 2SC372TM and 2SC373TM, it is strongly suspected that they are exactly the same products to 2SC1815 based on the description in “The Newest transistor standards tables”. The relationship between 2SA495TM and 2SA1015 may be the same to that among 2SC372TM, 2SC373TM and 2SC1815. Although we cannot know the exact reason why 2SC372 family and 2SA495 were continued to be produced even though the official names were changed and designated being maintaining/discontinued, there might have been needs for the products having same name by manufactures of application products.

As described above, there is good reason to believe that the 2SC1815, which has larger maximum ratings than the 2SC372 family and the same electrical characteristics, is a direct successor to the 2SC372 family.

Differences in the derivative varieties between 2SC372 family and 2SC1815

As already described, in addition to regular series, there had been derivative varieties for 2SC372 family, e.g. 2SC370G–2SC373G as‘Green Transistor for communications industry’, and 2SC370T and 2SC371T as a variety for RF power amplification in 27 MHz citizen band. The 2SC1815, on the other hand, did not have any derivatives for communications industry applications or for RF power amplification. It is difficult to know the details, but in the old days, it had been difficult to reduce the variation in electric characteristics due to inferior manufacturing technology, so they might have selected varieties that met certain criteria and treated them as varieties for the communications industry or for RF power amplification.

In contrast, there is a derivative variety 2SC1815(L), of which the noise characteristics were guarantied, for 2SC1815 (similarly, 2SA1015(L) for 2SA1015). Although the basic variety 2SC1815 exhibits sufficiently low noise figure, 2SC1815(L) exhibits even lower noise figure, which might be assumed to be a consequence of the development of manufacturing technology.

In addition, 2SC2458, a smaller packaged lead type, and surface mount devices (SMD), 2SC2712 (package: SC-59), 2SC4116 (package: USM/SC-70), and 2SC4738 (package: SSM) might be also regarded as a derivative variety of 2SC1815, because these exhibit the same electric characteristics to 2SC1815, although they have smaller Pc because of being differently packaged. Although 2SC2458, a lead-type variety, had been discontinued as same as 2SC1815, another three SMD varieties seem to be a currently produced variety.

The presumed backgrounds of 2SC1815 having been popular

As described until here, 2SC1815 should be regarded as the direct successor variety of 2SC372 family. Therefore, it should be necessary to keep in mind for consideration that 2SC372 family had been one of the most popular varieties of the general-purpose transistors in order to mention about the current status of 2SC1815.

Serialized articles entitled “Toshiba Radio School” targetting beginners who manufacture electronic equipments, in which semiconductor products of Toshiba were included, had been included as a public relation article of Toshiba in the monthly magazine “Shoho no Radio” [初歩のラジオ] being published by Seibundo-shinkosha Co. Ltd. [誠文堂新光社], Tokyo. I imagine that there had been many articles in which 2SC372 family had been applied, although I cannot be sure that since I possess very limited numbers of that magazine.

As already mentioned, in addition, the transistors manufactured by Toshiba had been advertised every time in the back cover of “The Newest transistor standards tables”, e.g. I can see that various types of newly developed “Toshiba silicon plainer type epoxy transistors” had been advertised in the back cover of the 4th edition of that, which was published in 1967, accompanied with recommended usage of each type.

Most manufactures of semiconductors usually manufactures applied electronic products, in which semiconductors are used, within own company or own groups. Among them, it is imagined that Toshiba had been also focused on outside sales, being inferred from the advertisement on the back cover of “The Newest transistor standards tables”. This may be one of the reason that 2SC1815 could became the most standard transistor.

References

1. ‘Testing performances of transistors made in China, which are extremely low price’ by T. Kato. “Tra-gi Jr.” No. 38, 2019 [加藤高広「中国製!激安トランジスタの性能テスト」『トラ技Jr.』No. 38，2019]

2. “Toshiba Semiconductor Hand Book (3)” Toshiba Co. Ltd. (ed.), Seibunto-shinkosha, Tokyo, 1966 [『東芝半導体ハンドブック(3)』東芝芝浦電気株式会社「東芝半導体ハンドブック」編集委員会（編），誠文堂新光社，東京，851 pp.，1966年9月20日発行]

3. “Toshiba Semiconductor Hand Book (1969 General edition)” Toshiba Co. Ltd. (ed.), Seibunto-shinkosha, Tokyo, 1968 [『東芝半導体ハンドブック（1969年総合版）』東芝芝浦電気株式会社（編），誠文堂新光社，737pp.，1968年発行]

4. “Toshiba Semiconductor Hand Book 1971 General edition” Toshiba Co. Ltd. (ed.), Seibunto-shinkosha, Tokyo, 1960 [『東芝半導体ハンドブック総合版1971』東芝芝浦電気株式会社（編），誠文堂新光社，804pp.，1970年発行]

5. “Toshiba Semiconductor Data Book (Transistors)” Toshiba Co. Ltd. (ed.), 1976 [『TOSHIBA SEMICONDUCTOR DATA BOOK（Transistor編）』東芝芝浦電気株式会社（編），1116 pp.，1976年9月発行]

6. “The Newest transistor standards tables” 1967, 1977, 1978, 1979, and 1981 editions. M. Tokita (ed.), CQ publishing Co. Ltd., Tokyo. [『最新トランジスタ規格表』（1967, 1977, 1978, 1979, 1981年版）時田 元昭 編，CQ出版株式会社]

© 2020 KOHNO Katsuyuki