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bc550 LTP values
bc550 LTP values
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Old 12th May 2020, 06:25 PM   #11
mchambin is offline mchambin  France
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Ultra low noise transistor measurements.
Ultra low noise amplifiers
Transistor junction temperature is not transistor case temperature.
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Old 14th May 2020, 12:06 AM   #12
Mark Tillotson is offline Mark Tillotson
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Originally Posted by peranders View Post
Do you have any datasheet that tells that?
Well I've built a test preamp using those transistors that detects the difference in Johnson noise between a 1 ohm and 3.3 ohm resistor as source, ie 0.2nV/√Hz of source voltage noise is not swamped by a ZTX851 or ZTX951

The transistors are actually designed as switching transistors with very low saturation voltage, which also happens to require very low Rbb.
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Old 14th May 2020, 12:47 AM   #13
sgrossklass is offline sgrossklass  Germany
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Horowitz/Hill 3rd ed. lists a sub-2 ohm Rbb' for both... they're pretty much the closest thing to the legendary 2SB737 left for super low impedance work, if without the same high beta. Super low Rbb' high beta transistors all seem to have gone the way of the dodo these days.

If a sub-10 ohm Rbb' will do in your application, ZTX450 and 550 seem like a more sensible alternative. There's a whole range of parts if ca. 30 ohms will do.
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Old 14th May 2020, 03:30 PM   #14
donovas is offline donovas  South Korea
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umm.. what about my ccs issue, guys?
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Old 14th May 2020, 10:17 PM   #15
Salas is online now Salas  Greece
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bc550 LTP values
Try 1K R1 R2 because modern red Leds usually have more than the 1.6V forward drop shown in the schematic
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