Very High-Gain PNP Transistors...

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#24
AndrewT said:
The many paralleled philosophy was to achieve extreme low noise performance.
The "matching", both thermal and electrical, is simply a give away consequence.
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Really? I have only used them in logarithmic amps and VCAs, long ago, for instrumentation, where the sole attraction was supermatching, to get an order of improvement on Motorola's then log. IC amps.
Just reviewing early Natsemi app. notes AN262 onward, I'm reminded that you don't see early audio apps for the LM394 so you may appreciate my different viewpoint, low noise instrumentation requirements notwithstanding.

Audio use is another matter, I guess, as they did get thrown into the front end of preamps and amps everywhere - only to be dropped a couple of models later, hardly seen since.

The NF is certainly low at 1nV/root Hz but no better than single transistor pairs in MAT02, SSM2210 etc. I have tended to think the low noise is a consequence of multiple transistors rather than my principal requirement of gain matching and low drift. When I eventually began to experiment with them in audio, the priority was LTP DC balance and NF was not particularly important, as we find in most commercial amplifiers.
 
#25
Ian Finch said:
Really? I have only used them in logarithmic amps and VCAs, long ago, for instrumentation, where the sole attraction was supermatching, to get an order of improvement on Motorola's then log. IC amps.
Just reviewing early Natsemi app. notes AN262 onward, I'm reminded that you don't see early audio apps for the LM394 so you may appreciate my different viewpoint, low noise instrumentation requirements notwithstanding.

Audio use is another matter, I guess, as they did get thrown into the front end of preamps and amps everywhere - only to be dropped a couple of models later, hardly seen since.

The NF is certainly low at 1nV/root Hz but no better than single transistor pairs in MAT02, SSM2210 etc. I have tended to think the low noise is a consequence of multiple transistors rather than my principal requirement of gain matching and low drift. When I eventually began to experiment with them in audio, the priority was LTP DC balance and NF was not particularly important, as we find in most commercial amplifiers.
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http://www.johnhardyco.com/pdf/990.pdf
 
#27
Hello,

I made measurements on some of my transistors.

I used a PeakMeter PM8233D DVM to measure Vbe, whilst measuring
Hfe with a Duoyi DY294 transistor tester, @ Ib = 10µA.

The 2SA640 were LTP extracted from an old power amplifier.
I don't remenber the brand.

The BC557B and BC560C were baught from an eBay chinese seller.
They were presented as matched transistors.

So ??
 

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#28
alayn91 said:
Hello,

I made measurements on some of my transistors.

I used a PeakMeter PM8233D DVM to measure Vbe, whilst measuring
Hfe with a Duoyi DY294 transistor tester, @ Ib = 10µA.

The 2SA640 were LTP extracted from an old power amplifier.
I don't remenber the brand.

The BC557B and BC560C were baught from an eBay chinese seller.
They were presented as matched transistors.

So ??
Click to expand...
what are the digits that look like an inverted "V"?
How did you measure VBR ce0?
 
#34
alayn91 said:
Hello,
Right, I didn't understand your question !
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The way you wrote "1" is like inverted "V". I had no problem reading it even tho I didn't know about any European style.

I don't know why you made the test, as BC550c/560c is pretty standard low noise high gain (typically above 500) transistors, and OP seemed to want something better than that.

BUT, important information from your test is that they actually have such a high break down point!! (74v?). I have also believed that the rated max SOA characteristics in the datasheets are underrated for original products from top manufacturers. That's why I use Vceo=45V device all over the places.
 
#36
C grade is the highest grade having hfe from 420 to 800. It is normal that some manufacturers produce typically lower than others. It is also often found that once in a while ON semi can perform better than the published maximum (in this case 800)
 
#37
Ian Finch said:
I don't think so. LM394 is a multiple transistor, with many parallel transistors formed on the one substrate to achieve otherwise impossible matching by virtue of averaging the individual junction properties.

You won't get anywhere near that match quality or low drift without extremely precise matching of duals, also on the same substrate. Then again, if you don't really need the "supermatch" properties, you may find these useful, if also obsolete: Page Not Found | Analog Devices
Page Not Found | Analog Devices

You can still obtain LM394H if necessary - there are a few realistic opportunities on the net with a little help from Google. However, this recently revised doc. by TI suggests some renewed manufacturing interest: http://www.ti.com/lit/an/snoa626b/snoa626b.pdf
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sir what is good replacement for 2SA1240 thank you so much sir
 
#38
desertstorm said:
sir what is good replacement for 2SA1240 thank you so much sir
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If you can't find the real deal, they're basically two ECB pinout transistors side by side - you could epoxy together two KSA992 or similar to obtain the desired pinout (or maybe solder in first, then epoxy). Much like what people are doing to replace 2SA798s, except easier. Should the whole thing get too thick, you could probably sand off some of the rounded back.
 
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