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發表於 14-10-2009 14:45:00
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The maker of the original 300B is Gray & Barton, an old company founded (before radio came on the scene) to make telephone equipment. Gray & Barton became Western Electric Manufacturing Company in 1872. It was reorganized in 1881 as the Western Electric Company. One year later the Western Electric Company became the manufacturing division of Bell Telephone.
Western Electric Export Corporation was formed in 1928 to be Western Electric's foreign distributor and its marketing arm for audio equipment and parts. The company became Westrex Corporation in 1942. Litton Industries acquired part of Westrex in 1958.
Convinced of the viability of tubes for amplification of telephone messages, Western Electric began producing them back in 1912. Those early tubes operated telephone repeaters and were first installed in 1913. The original Type A of 1912 to 1913 resembled the DeForest spherical Audion but without the screw-in base; instead, wires extended directly from the base. Since then, Western Electric has manufactured many tubes, most of them for industrial, military, and telephone use.
The 300A and 300B
The 300A tube, precursor to the 300B, was first manufactured in 1933 by Western Electric. The 300B appeared on the scene in 1938, identical to the 300A, except that the bayonet pin in the base was rotated 45 degrees so that the 300B could serve as a replacement for the 205A. The 300A/B had a 5-volt, 1.2-amp filament and a maximum plate voltage of 480 volts. The listed typical characteristics for class A operation are 300 volts at 60 mA with an amplification factor of 3.8 and a power output of 6 watts. Most amplifier builders today run the 300B at higher plate voltages. I scanned a number of recent single-ended triode amplifier designs and noted plate voltages from 337-475 volts, all above the rather conservative ratings of the Western Electric Electron Tubes-General Bulletin recommendation.
Western Electric used the 300A/B in the 27A transmitter and the 86A, 86B, 86D, 87A, 91A, and 92A amplifiers, for other military equipment, and for amateur radio. Many movie theaters had 300A/B tubes in their sound systems.
Beyond their obvious use in audio amplifiers, 300Bs found their way into power supplies as voltage regulators. Every once in a while one still turns up in an old junker power supply; unfortunately, I have not been lucky enough to find one that way.
The tube number and name is etched on the base of every 300A I have seen. Western Electric printed the number and name in yellow lightning bolt on early 300Bs. In the 1970s, plain printing replaced the lightning bolt logo. The last batch of tubes returned to the old logo.
Several characteristics have endeared the WE 300B to those of us who are interested in high quality audio sound. In the thirties, no other tube had as much output as the 300B. except for a transmitting tube. The Western Electric 205D could produce about one watt. The same was true of the 45. The 50 tube doubled the output of the 45, but the 300B produced six to eight watts in single-ended operation.
The longevity of the WE 300B is one of its finest characteristics. It is estimated on average to last nearly 40,000 hours. Another important characteristic of the WE 300B is its very low distortion. For example, Eric Barbour tested the WE 300B and found the internal distortion to be one-third that of a RCA 250 tube.
The reissue 300Bs look very much like the old ones, both externally and internally. An outline drawing and base detail of the 300B are shown in Figure 2. The new tube has a round wire getter, while each of the two older 300Bs in my possession has a different type of rectangular getter. My 300A has a still different getter. It is my understanding that some of the later original 300Bs had a round getter as well. |
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發表於 11-10-2009 22:36:52