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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Re: tubes vs. transistors, posted by Dan Banquer on July 17, 2006 at 09:19:58:
Hi DanFor a generic complementary output transistor pair like the 2N3055a / MJ2955A the current gain is unity (base current equals collector current) at about 800KHz.
The typical gain at DC is specified as 20 to 70.
In this case, if the device had a DC gain of 64 and ft of 800KHz, then the open loop corner would be approximately 12.5KHz.
For the darlington pair of MJ4035 / MJ4032, the ft is 1MHz, and has a specified DC gain of 1000.
Here, the open loop corner would be around 1KHz.
Don’t get me wrong, I’m not saying you can’t find better transistors but the 3055 was rugged and used in zillions of amplifiers (as well as its bigger NPN only brother the 2N3773).You can approximate all this if take the transistor’s ft and figure the gain here is 1 and recall it increases by 2 times each time you lower the frequency from ft an octave.
The DC gain extends upward in frequency (approximately) to the intersection of this slope and this is the open loop corner for the device.
Thanks for an actual technical discussion, too much of this forum is a Monty Python argument sketch.Tom
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Follow Ups
- Re: tubes vs. transistors, - tomservo 11:19:12 07/17/06 (1)
- Re: tubes vs. transistors, - Dan Banquer 11:34:43 07/17/06 (0)
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