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Old 21st March 2011, 10:28 AM   #1551
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Where is everyone?
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Old 21st March 2011, 10:52 AM   #1552
AndrewT is offline AndrewT  Scotland
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away buying and/or reading the book.
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Old 21st March 2011, 11:57 AM   #1553
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Originally Posted by Olivier73 View Post
Where is everyone?
Hi Olivier,

I've been a bit remiss lately in keeping the thread going and I apologize for that. I've been doing some traveling (some to promote the book), but also working very hard to finish up a bunch of new material that I want to put up on my web page in support of the book. Much of the effort has concerned the finishing up up more and refined transistor SPICE models. Noise measurement work for the numerous transistors and translating that into SPICE model numbers took quite a bit of time.

I just got back last night from the Midwest Audio Engineering Summit at Webster University in St. Louis where I gave a lecture on power amplifier design. It was a nice experience to interact with so many enthusiastic students who are going into audio engineering. BTW, this more means the context of mixing and producing recorded and live sound than electrical engineering. It was also very nice interacting with many of the other speakers, who included many very accomplished engineers and producers in the audio entertainment business.

If you have any topics you'd like to discuss or questions you have, I'm here to answer them.

Cheers,
Bob
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Old 21st March 2011, 01:35 PM   #1554
PB2 is offline PB2  United States
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Originally Posted by Bob Cordell View Post
Hi kenpeter,
I'm still trying to finish up the new group of model updates I will be posting on my website. Almost every time I look at modeling I get angry with the manufacturers because their models are so awful. Look at the MJE340/350 spec sheet - they don't even quote ft, much less provide a graph of it.

Cheers,
Bob
I have some older Motorola data books that also list the MJE341/344 which are lower voltage versions but they provide more data: Cob=15pF, Ft = 15MHz at 50 mA 10V.
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Old 22nd March 2011, 02:09 PM   #1555
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I have some older Motorola data books that also list the MJE341/344 which are lower voltage versions but they provide more data: Cob=15pF, Ft = 15MHz at 50 mA 10V.
Hi Pete,

Thanks for this info. About two weeks ago I actually measured some MJE340 and 350 transistors for ft out of desperation. I was very surprized to get 18 MHz for the NPN MJE 340 but 30 MHz for the PNP MJE350, both at 20mA, 10V. As you know, PNP transistors are more often slower than the complementary NPN device.

Cheers,
Bob
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Old 22nd March 2011, 03:17 PM   #1556
jcx is online now jcx  United States
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my understanding was that hgiher electron mobility in N doped Si gave PNP an advantage in speed, noise from lower r_bb, r_x base resistance

holds for driver sized Q, maybe large output Q design has other tradeoffs?
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Old 22nd March 2011, 04:31 PM   #1557
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Originally Posted by Bob Cordell View Post
Hi Pete,

Thanks for this info. About two weeks ago I actually measured some MJE340 and 350 transistors for ft out of desperation. I was very surprized to get 18 MHz for the NPN MJE 340 but 30 MHz for the PNP MJE350, both at 20mA, 10V. As you know, PNP transistors are more often slower than the complementary NPN device.

Cheers,
Bob
Interesting about the MJE's My EX uses them correctly , I see (PNP active , NPN CCS). Everyone makes fun of these classic devices , but I have found they work excellent as a VAS device , even with higher Cob/lower Ft. Not the case with 1381/3503 or 992/1845 pairs ... nearly identical Ft - different manufacturing process.

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Old 22nd March 2011, 10:53 PM   #1558
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Originally Posted by jcx View Post
my understanding was that hgiher electron mobility in N doped Si gave PNP an advantage in speed, noise from lower r_bb, r_x base resistance

holds for driver sized Q, maybe large output Q design has other tradeoffs?
Hi jcx,

I've just always assumed PNPs were slower, and most whose specs I've seen appear to be smaller, including small-signal devices. I'm pretty sure that's been my experience with linear IC transistors built in complementary processes as well. It would seem that the N-type base of a PNP would help make it faster due to higher mobility in the base, but there may be other factors at work that turn the tables. I have, however, usually seen lower rb in PNP devices.

Cheers,
Bob
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Old 25th March 2011, 06:49 PM   #1559
PB2 is offline PB2  United States
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Quote:
Originally Posted by Bob Cordell View Post
Hi Pete,

Thanks for this info. About two weeks ago I actually measured some MJE340 and 350 transistors for ft out of desperation. I was very surprized to get 18 MHz for the NPN MJE 340 but 30 MHz for the PNP MJE350, both at 20mA, 10V. As you know, PNP transistors are more often slower than the complementary NPN device.

Cheers,
Bob
That is pretty good agreement. Did you use the method described in
MIL-M-38510/108A page 12?
http://www.dscc.dla.mil/Downloads/Mi...38510ss108.pdf

That is done at 100 MHz, did you measure at 1 or 10 MHz, or ... ?
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Old 26th March 2011, 12:20 AM   #1560
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Originally Posted by PB2 View Post
That is pretty good agreement. Did you use the method described in
MIL-M-38510/108A page 12?
http://www.dscc.dla.mil/Downloads/Mi...38510ss108.pdf

That is done at 100 MHz, did you measure at 1 or 10 MHz, or ... ?
Hi Pete,

I measured AC beta at 500kHz, 1MHz and 2 MHz, all at both 1mA and 10mA. This is similar to the method described, except for the measurement frequency. Basically, I biased up the transistor with a 100-ohm load and fed a voltage from a test oscillator through a high resistance into the base. I used an HP652 test oscillator and an HP 400EL AC voltmeter. So basically I put in a known AC current and inferred the AC collector current by looking at the AC voltage at the collector.

Cheers,
Bob
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