2N2222A transistor and transisitor history - Page 11 - diyAudio
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Old 30th January 2010, 12:09 AM   #101
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I never learn to stop feeding the trolls.
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Old 30th January 2010, 12:23 AM   #102
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Ivey, what I never completely understood was the bilateral transistor made for choppers. The MPS404A seems to be one of these devices. Isn't this the quality that made this device useful? Certainly, nothing else.
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Old 30th January 2010, 12:37 AM   #103
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Quote:
Originally Posted by john curl View Post
Ivey, what I never completely understood was the bilateral transistor made for choppers. The MPS404A seems to be one of these devices. Isn't this the quality that made this device useful? Certainly, nothing else.
Good John not many people remember this. A backwards transistor has 0 Vsat and makes a good chopper switch. This transistor had an ft of 4Mhz hardly RF.
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Old 30th January 2010, 01:22 AM   #104
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Originally Posted by scott wurcer View Post
Good John not many people remember this. A backwards transistor has 0 Vsat and makes a good chopper switch. This transistor had an ft of 4Mhz hardly RF.
Yes, when I first joined Plessey Semi in the UK in '63, they were just starting up a planar line licenced from Fairchild and went straight in with the '702 and a lot of ECL MIL (flatpack) parts. I think they bought the whole plant from Philco. ? anybody remember?

They still had the old acid etch line (mechanical timers, acid and god knows what squirting everywhere! Nightmare!!

Anyway, one device that still sold at a premium was a silicon symetrical device used as a chopper. In fact I prototyped (although I didn't really know what I was doing!) an "op-amp" using input and output choppers and AC gain to make a very respectable DC moving coil meter amplifier.

Scott - agreed about the trolls; difficult to resist with such mis-information.

Cliff (getting older by the day.)
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Old 30th January 2010, 01:30 AM   #105
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Originally Posted by cliffforrest View Post

Cliff (getting older by the day.)
Wow 1963, you must be of the Barrie Gilbert vintage. For me it's the big 60 on Monday.
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Old 30th January 2010, 03:40 AM   #106
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Ivey, what are currently the best audio transistors?
I have the 2N5088 and 2N5099 with lower NF=3 dB.
What about JFETs? I don't like the way they sound for audio personally, too brittle.
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Old 30th January 2010, 04:23 PM   #107
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Ah, the UA702! Used to get them from Fairchild, back in 1965, or was it 1966? ;-)
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Old 30th January 2010, 06:26 PM   #108
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Barrie was at Mullard in Southampton and I used to visit him there - I was just a young oik, so I doubt if he would ever remember me.

702s were a real pig to wafer test. In those days we had only semi-automatic wafer probers with individual wired probes, so no performance boards. Just a kludge of stuff trying to stop the DUT from oscillating, which it usually did due to the process being all over the place. I mean, step and repeat was MECHANICAL!!, with the camera on a few tons of concrete to try and damp the vibrations.

Kids these days, don't know what ......

Cliff, 66 and rising
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Old 30th January 2010, 06:58 PM   #109
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A girlfriend of mine was on final test for the 702 and 709, back in 1965. I tried to hire in to Fairchild in 1963, but was turned down. I think that Bob Widlar interviewed me.
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Old 30th January 2010, 07:02 PM   #110
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I used to test complete 702's and 709's at Friden in 1966. We built a test analyzer that Fairchild published as a schematic at the time. I was in charge of 100's of units, tested them all, myself. I had technicians that worked for me, but this was delicate work. Learned lots of good things.
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