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 Post subject: Strange issue
PostPosted: Jun Wed 08, 2022 5:17 am 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 9420
Location: ID 83301
Working on a typical 60s Japanese transistor pocket radio with center window dial , round speaker grille branded brownie . This radio was definately used alot . Odd thing is I recap and it worked ok . It had a strange issue with sometimes working better then not . Then after shining it all up it quit . To make a long boring story short I found one 2sa31 transistor in wrong . Why it worked at all period was strange .


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 Post subject: Re: Strange issue
PostPosted: Jun Wed 08, 2022 6:39 am 
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Joined: Feb Mon 21, 2011 3:19 pm
Posts: 578
Location: San Marcos, CA 92069
Surprisingly older germanium transistors often will work even if the emitter and collector leads are swapped. The hFE (gain) will be reduced, but will still be high enough for some circuits to work.


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 Post subject: Re: Strange issue
PostPosted: Jun Wed 08, 2022 3:19 pm 
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Joined: Oct Mon 26, 2009 9:02 pm
Posts: 7592
Location: Indianapolis, IN
Hey Ken---Nash is right ! Does it work well after replacement ?

A friend bought an earlier Raytheon 8TP and said that one of the transistor sockets was installed "backwards" and it had an odd audio issue, but did work somewhat.

John


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 Post subject: Re: Strange issue
PostPosted: Jun Thu 09, 2022 1:07 am 
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Joined: May Tue 30, 2006 3:46 pm
Posts: 11458
Location: Santa Rosa, CA
All transistors have "reverse" hFE. It's usually very low and can be less than one.

Quote:
Reverse Current When ON

In an NPN transistor, the Base is at a positive bias, the Collector at a negative bias, and reverse current flows from the Emitter to the Collector. Also, please consider problems that may arise from usage as transistors (such as smaller current gain).Transistor Reverse current when ON

1.It has been determined that no problems, such as degradation or destruction, will arise from use.

2.In the case of an NPN transistor, B is symmetrical with C, and E with N. Therefore, C and E can be used as a transistor, even when connected in reverse. In this case current will flow from E to C.


Transistor Normal OperationTransistor Reverse Operation


3.The following are characteristics of transistors connected in reverse.

Low hFE (approx. 10% of the value of the forward direction)
Low voltage resistance (around 7-8V, about the same as VEBO) The voltage may even be lower (below 5V) in some standard transistors (Please consider that excessively low voltage resistance may result in breakdown and degradation of characteristics)
VCE(sat) and VBE(ON) should not change much


The circuit images didn't copy, so see this explanation:

https://www.rohm.com/electronics-basics/transistors/understanding-transistors

Rich


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 Post subject: Re: Strange issue
PostPosted: Jun Thu 09, 2022 6:07 am 
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Joined: Feb Mon 21, 2011 3:19 pm
Posts: 578
Location: San Marcos, CA 92069
Early germanium transistors were made from a slice of N type germanium with a small dot of indium on both sides that was heated so it diffused slightly, forming P type doped junctions. Often the collector dot was larger than the emitter dot, but not always.

The difference between forward current gain and reverse current gain is a related to the asymmetry of the two junctions (E-B and C-B). Early transistors, especially alloy junction germanium transistors were very symmetrical, and the reverse gain could approach the forward gain.


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 Post subject: Re: Strange issue
PostPosted: Jun Wed 15, 2022 3:44 am 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 9420
Location: ID 83301
It worked but not good . I just put the original transistor in the right way then it was fine .


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