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 Doc Oc or the Octopus Woes.

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FrankB
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PostSubject: Doc Oc or the Octopus Woes.   2016-09-17, 7:59 pm

So I built a basic "Octopus" for testing semi junctions, to look for unmarked zeners and other types.

Just a 6.3 v fil transformer, a couple of resistors, 330 and 3300 ohms, and a scope to see the junction on.
  Well..... I blew all to snarglefritz a handful of germanium diodes. Blew out the junctions completely. Embarassed Mad

 These were old, small signal types. Best guess was that the current flowing thru the 3300 ohm resistor was way too much for the diodes to handle. (I can't believe 20+ NOS diodes were bad!!).

So back to the Huntron Tracker & the trusty old B&K 501 for me.

Just a warning that "simple" test equipment can have undesired effects on components.
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Cliff Jones
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PostSubject: Re: Doc Oc or the Octopus Woes.   2016-09-17, 9:07 pm

Now the question is:
Is there anyway to Identify unmarked signal diodes?
Or maybe limit the current divider resistance to microamps to use to start with using the Octpus, wth a switch for switching to heavier diodes as the second testing method.

Raises a subject worth researching.
2 signal diodes are the 1N4148, 
The maximum current is 150 mA.
I don't know if this is a general rule, but aren't most signal diodes encapsulated in glass?
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and the 1N914.
The maximum forward voltage is about .3 volts
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I just found a new term for clamping diodes, in microprocessors they are called FREEWHEELING DIODES.

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FrankB
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PostSubject: Re: Doc Oc or the Octopus Woes.   2016-09-18, 10:09 pm

Yes, there is a way to test unmarked diodes.

A curve tracer, or factory test equipment.
 An ohmmeter will tell you if its germanium or silicon though.
OTT - Well without a curve tracer I know of no real way to test diode voltage ratings UNLESS they are zeners. (See my posting on testing them with an eye type cap. checker on this site).

 Silicon stacks like that were used for HT rectifiers and focus diodes --s u p p o s e d l y --can be given a go-no go test using a light bulb for current limiting and a HV source. Personally, I have my doubts on that method, although a TV repair journal did tout it. Typically TV type HT rectifiers are good for about 2 MA., IIRC. A bulb would use a lot more current.
If I could remember where I saw the circuit, I'd post it. I do not recommend trying that method though.

Signal diodes were either glass or metal- (Typically WE)-  encapsulated. There might have been some top hat types too, but in the beginning, I think they used whatever case they could. (I do have some 1N34 & 1N60 types in ceramic, as well as 1N23,A ones too. Huge casings compared to todays glass casings.)
 Now the 1N4007 can replace the huge ceramic and selenium rectifiers they used in TV sets power supplies "Way back when". (See my article on full length leads and current de-rating for diodes posted on this site too).
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