Unmarked transistor identification. - UK Vintage Radio Repair and Restoration Discussion Forum

poppydog · 8th May 2018, 12:24 pm

I have a metal cased npn transistor that has no marking on it, how can I tell if its ge or silicon?

regards poppydog

Argus25 · 8th May 2018, 12:55 pm

Typical digital meter with a diode/beep setting will give about 0.35V on the base emitter connection for germanium and about 0.65v for silicon

Or, if you just have a volt meter, set up a battery, say 9V with a series resistor say 10k to forward bias the base-emitter junction and measure its voltage drop, will be around 0.3v for germanium and 0.65v for silicon.

Probability dictates its a silicon, as NPN germaniums are not wonderfully common, but it still could be one.

poppydog · 8th May 2018, 1:02 pm

Thanks for that Argus25

regards poppydog

poppydog · 9th May 2018, 9:37 am

What happens if the transistor is knackered, how do you identify it then?

regards poppydog

Mooly · 9th May 2018, 9:44 am

You can only do basic tests such as for leakage, forward gain and so on.

Without knowing what it is, its impossible to go further. For example some small signal RF types have very limited voltage and current ratings, perhaps as low as 12 volt and 50ma.

As its unmarked, how did you determine it to be NPN ? (just curious

)

poppydog · 9th May 2018, 10:09 am

I asked what would happen out of curiosity, the transistor in question was very low gain as indicated on a transistor tester

regards poppydog

kellys_eye · 9th May 2018, 10:40 am

The cheap multi-device testers from your 'local' Chinese supplier will give you all the basic parameters of such devices. Pinout, polarity, gain, Vbe etc.

They are, imho, the most useful pieces of test equipment anyone can have these days - they come into their own (for my purposes) when trying to identify the pinout of the TO92 devices which are often confusing despite datasheet information!

For around a tenner you can't go wrong.

Mooly · 9th May 2018, 12:51 pm

Quote:

Originally Posted by poppydog

I asked what would happen out of curiosity, the transistor in question was very low gain as indicated on a transistor tester

Thanks, I just wondered that's all.

Using a DVM (or analogue meter... an AVO8 is great for general transistor checking) takes only a few seconds to identify NPN or PNP, and the analogue meter on a high ohms range can be a good guide for testing for leakage.

True low gain (with no other problems such as being leaky) is not all that common a failure mode in my experience.

8th May 2018, 12:24 pm	#1
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Unmarked transistor identification. I have a metal cased npn transistor that has no marking on it, how can I tell if its ge or silicon? regards poppydog

8th May 2018, 12:55 pm	#2
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: transistor identification Typical digital meter with a diode/beep setting will give about 0.35V on the base emitter connection for germanium and about 0.65v for silicon Or, if you just have a volt meter, set up a battery, say 9V with a series resistor say 10k to forward bias the base-emitter junction and measure its voltage drop, will be around 0.3v for germanium and 0.65v for silicon. Probability dictates its a silicon, as NPN germaniums are not wonderfully common, but it still could be one.

8th May 2018, 1:02 pm	#3
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: transistor identification Thanks for that Argus25 regards poppydog

9th May 2018, 9:37 am	#4
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Unmarked transistor identification. What happens if the transistor is knackered, how do you identify it then? regards poppydog

9th May 2018, 9:44 am	#5
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Unmarked transistor identification. You can only do basic tests such as for leakage, forward gain and so on. Without knowing what it is, its impossible to go further. For example some small signal RF types have very limited voltage and current ratings, perhaps as low as 12 volt and 50ma. As its unmarked, how did you determine it to be NPN ? (just curious )

9th May 2018, 10:09 am	#6
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Unmarked transistor identification. I asked what would happen out of curiosity, the transistor in question was very low gain as indicated on a transistor tester regards poppydog

9th May 2018, 10:40 am	#7
kellys_eye Octode Join Date: Jan 2014 Location: Oban, Scotland, UK. Posts: 1,129	Re: Unmarked transistor identification. The cheap multi-device testers from your 'local' Chinese supplier will give you all the basic parameters of such devices. Pinout, polarity, gain, Vbe etc. They are, imho, the most useful pieces of test equipment anyone can have these days - they come into their own (for my purposes) when trying to identify the pinout of the TO92 devices which are often confusing despite datasheet information! For around a tenner you can't go wrong.