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本帖最后由 ulgsm4u 于 2012-5-30 13:13 编辑
原文在这里：
http://www.tcaas.btinternet.co.uk/jlh1969.pdf
John Linsley Hood 的原话是 “选什么管， 不重要。。。”
{
Suitable transistors
Some experiments were made to determine the extent to which the circuit performance was influenced
by the type and current gain of the transistors used. As expected the best performance was obtained
when high-gain transistors were used, and when the output stage used a matched pair. No adequate
substitute is known for the 2N697 / 2N1613 type used in the driver stage, but examples of this transistor
type from three different manufacturers were used with apparently identical results. Similarly, the use of
alternative types of input transistor produced no apparent performance change, and the Texas
Instruments 2N4058 is fully interchangeable with the Motorola 2N3906 used in the prototype.
The most noteworthy performance changes were found in the current gain characteristics of the output
transistor pair, and for the lowest possible distortion with any pair, the voltage at the point from which the
loudspeaker is fed should be adjusted so that it is within 0.25 volt of half the supply line potential. The
other results are summarized in Table 2.
The transistors used in these experiments were Motorola MJ480 / 481, with the exception of (6), in which
Texas 2S034 devices were tried. The main conclusion which can be drawn from this is that the type of
transistor used may not be very important, but that if there are differences in the current gains of the
output transistors, it is necessary that the device with the higher gain shall be used in the position of Tr1.
When distortion components were found prior to the onset of waveform clipping, these were almost
wholly due to the presence of second harmonics. }
John Linsley Hood 是个科学家， 不是玄学家。 |
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楼主
发表于 2012-5-30 09:32
