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Western Electric 300B Tube article
300B The lights are dim. Several tube audiophiles stand around someone amplifier, conversing in reverential tones. They must be talking about the Western Electric 300B. No tubend possibly no componentn the world of tube audio has attracted so much attention over the years than the 300B triode from Western Electric. Some of the finest audio amplifiers in the world use it even today.
The last Western Electric 300B tube rolled off the assembly line in 1988. Was it the end of an era? Some people feared it was. After all, almost everyone had switched to solid state amps. Only a small group of tube audio aficionados recognized that some of the finest reproduced sounds still emanate from well designed tube amplifiers. Many of their amplifiers used the Western Electric 300B. After 1988, WE 300Bs became very scarce. Tube collectors and audiophiles throughout the world hoarded every original 300B that they could get their hands on.
Other manufacturers began producing their own versions of the 300B in an attempt to fill the void. Early in 1995, Westrex Corporation announced the reintroduction of the Western Electric 300B, but a series of delays slowed the actual reissue until the spring of 1997. The Westrex people claim to make the new 300B with the same quality materials and some of the same manufacturing molds and tooling as the old Western Electric 300B. They manufacture the tubes in the same Kansas City plant where they were previously made. Even twelve of the same employees who worked on the old 300Bs--most working on that particular tube for over 30 years�-are now helping to manufacture it.
The Western Electric Company
I became interested in the history of the Western Electric 300B when I first learned that it was to be manufactured again. I wondered whether the new Western Electric 300B really could be as good as the old classic power tube. The maker of the original 300B is an old company, Gray & Barton, 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 foreign distributor and its marketing arm for audio equipment and parts. It 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. Thereafter 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 (see pictures x&y). It 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.
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. 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 lightening bolt on early 300Bs. In the 1970s, plain printing replaced the lightening 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 without the use of 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 (see picture z). The new tube has a round wire getter, while the two older 300Bs in my possession each 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. On one of my review tubes I noticed a partial crack in the glass where the outer posts of the tube are pinched into the glassost likely it occurred in shipping rather than in the tube manufacturing process. I noted no such cracks in my older 300Bs. The reissue has the lightening-bolt print estern Electric, Made in USA 9552, 300B� on the base. Each tube has its own serial number etched into the base new feature.
Each reissue tube comes with a card listing its serial number and the test results for that specific tube: interelectrode capacitances; filament, plate and grid current; plate resitance; grid-plate transconductance; amplification (Mu); delta transconductance at 4.5 volts; and plate curves for the plate current versus plate voltage. Each matched pair is shipped in a mahogany-stained wood box, sealed with a tag bearing the serial numbers of the tubes inside. They look elegant, but they ought to: their price is $800 for a matched pair.
Single-Ended Triode Amplifiers
American audiophiles are renewing their interest in the use of triode audio amplifiers. The Japanese and some Europeans were there before we were. Most of the old 300B tubes now are in Japan, since most U.S. audiophiles had little interest in them and happily sold them for favorable prices to foreign collectors. The attention now given to tube amplifiers (especially using the 300B) is shifting from push-pull amplifier circuits of the Macintosh, Dynaco, Heathkit, and others popular in the late fifties and sixties, to single-ended triode circuit designs without the use of any feedback. Most amplifier sections in the very early radios and many early amplifiers used this single-ended triode design. In the middle of the century, push-pull circuit amplifiers took over from single-ended circuitry because they could produce more power (and frequently less distortion) from the tubes. There was more bang for the buck. Push-pull were cheaper per watt to produce than single-ended designs. A 300B tube would have double the watt output in push-pull circuitry than it would in a single-ended circuit. However, many tube audio builders believe that a pure and more listenable sound is generated by single-ended triode/no feedback circuitry.
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發表於 2012-4-24 02:10
樓主
Peter 真係識做!
