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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 4th Apr 2018, 8:03 pm   #1
poppydog
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Default Unknown transistor result?

I was wondering if anybody would be able to tell me what my transistor tester is telling me as I seem to have an extra test result. It seems to have performed a diode test between the collector and emitter and has given the results along with all the other usual tests it does. The transistor is an OC614 its the 1st FM IF Amp -AM conv from my Akkord. It doesn't do it on any other of the transistors that I have i.e. good ones.

See pic.

Regards Poppydog
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Old 4th Apr 2018, 8:14 pm   #2
paulsherwin
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Default Re: Unknown transistor result?

My guess would be a faulty transistor is confusing the tester.
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Old 4th Apr 2018, 8:45 pm   #3
Oldcodger
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Default Re: Unknown transistor result?

I'd tend to agree with paul. Have you tried a basic test on the junctions with something like an Avo, on ohms range. b-e and b-c should give about half scale with one polarity ( ref b-e/c) and OC the other way, with OC c-e in both directions. Any reading c-e would indicate a leaky junction and a suspect device. I presume that the device has been tested out of circuit, as other components in circuit will /may cause false readings.
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Old 4th Apr 2018, 11:21 pm   #4
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Default Re: Unknown transistor result?

Low voltage germanium transistors tend to have a little bit of leakage.
It is just seeing a little bit of difference in leakage between the two junctions.
That kind of component tester is of a design that is meant for silicon devices and may well give odd readings with germanium parts.
Mine shows about half of all good germanium parts as faulty and is very intermittent if any of the lacquer is scratched on an early Mullard transistor.
It goes crazy with a germanium photo transistor.
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Old 4th Apr 2018, 11:33 pm   #5
paulsherwin
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Default Re: Unknown transistor result?

I agree that modern testers and component analysers are often confused by Ge devices, both transistors and diodes. There may be nothing wrong with the transistor in question.
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Old 4th Apr 2018, 11:54 pm   #6
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Default Re: Unknown transistor result?

Oh that photo transistor under a ring tube magnifier lamp.
There must have been loads of 100hz ripple on the reading.
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Old 5th Apr 2018, 3:59 pm   #7
orbanp1
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Default Re: Unknown transistor result?

Hi Poppydog,

These testers are based on the following open source project:
https://www.mikrocontroller.net/arti...ansistortester
The Chinese eBay versions use the same measurement principles except the display got progressively updated to various graphics displays.

The measurement principles, and other details, are described in the following document:
https://github.com/svn2github/transi...er_eng112k.pdf
That document on pg. 70 describes the difficulties of measuring Ge BJT devices.
Despite of this, that transistor (and other components) tester is an amazing tool for what it is and for how little it costs!

It is also worthwhile to check out the long running thread on the EEVblog forum about these testers (especially if you want to upgrade your tester):
http://www.eevblog.com/forum/testgea...ecker-project/

As for measuring Ge transistors it is possibly better to use an "old school" transistor tester, or rig up your own measurements.
One of the "sticky postings" on this forum details transistor measurements.

Regards, Peter
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Old 19th Apr 2018, 9:45 pm   #8
poppydog
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Default Re: Unknown transistor result?

Thanks for all the replies, especially Peters (Orbanp1) reply with the links. Curiosity has got the better of me though so I’ve had a look through some of my faulty transistors that I keep (for some strange reason ) and have found only 1 that the tester performs that extra test on, it’s a faulty Ediswan XC101 from my ultra tr100 (see pic).
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It doesn’t seem to perform this test on some faulty AC187s that I have though??
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They are very useful testers though it would be nice if they could identify transistors as well as I have a few here that are missing their numbers so I have no idea what they are .

Regards
Poppydog
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Old 20th Apr 2018, 8:17 am   #9
John_BS
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Default Re: Unknown transistor result?

I'd be inclined to say your original transistor is OK: it has plently of gain, and not unreasonable leakage. Note that the "diode" result comes as a result of applying reverse polarity collector-emitter, so is perhaps not relevant for most applications.

John
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