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 Post subject: Transistor Question
PostPosted: Jan Sat 13, 2018 3:40 am 
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Location: new hyde park ny usa
Do transistors weaken with use like tubes do? Is it possible for 'weak' transistors to effect radio operation? Thanks AL


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 Post subject: Re: Transistor Question
PostPosted: Jan Sat 13, 2018 3:43 am 
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No they do not weaken, generally older transistors (1950's - 1970's) may fail due to "tin whisker" growth.

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 Post subject: Re: Transistor Question
PostPosted: Jan Sat 13, 2018 1:10 pm 
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Some of the early germanium transistors can develop "leakage" which can affect performance to various degrees. This can result in noise or reduced amplification.

Dave


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 Post subject: Re: Transistor Question
PostPosted: Jan Sat 13, 2018 2:26 pm 
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S/S devices and vacuum tubes have radically different failure mechanisms...(how's that for a profound statement?...;) )

If there are flaws in the manufacturing process, a transistor can develop leakage or some other anomaly after some combination of time and stress.**. In critical military and space applications, devices are screened for such issues...using some combination of operating parameters and temperature cycling.

A transistor can also be damaged by a current surge or overheatirng...resulting in, e.g., an increase in C-E leakage, while still having useful gain.

And there are the electro-chemical issues such as tin whiskers and something that was called "purple plague"
https://en.m.wikipedia.org/wiki/Gold-al ... ermetallic

**for example, local thermal gradients an temperature cycling create mechanical stress in the crystal structure.

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 Post subject: Re: Transistor Question
PostPosted: Jan Sun 14, 2018 10:53 am 
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They can weaken with age. I built a Philmore two Transistor receiver in 1958, which of course used Germanium Transistors. In trying to operate it a few years back, I noticed a distinctive decrease in performance, even after swapping the Electrolytic caps out.
Now exactly what caused the decrease I can't say, but that was the result.

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 Post subject: Re: Transistor Question
PostPosted: Jan Sun 14, 2018 2:27 pm 
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This very topic was discussed on another forum quite recently.
For whatever reason, I just can not find that thread.
I did save though a paper referred to there which describes the fail mechanism in transistors.
Find enclosed the paper.

EDIT:
As a corollary to this, I have been looking at an older (early '80s) radio of mine, a Realistic 14-920A (very good FM tuner in it), that has quite a high hissing background noise that does not vary with changing the volume.
see: https://www.radiomuseum.org/r/radio_shac_concertmate_8_14_920b.html
I did replace two questionable (by ESR) electrolytic caps in the audio amp, that did not make things any quieter.
That radio uses the LA4201 chips as audio amps. I am wondering may be those chips are the ones that are noisy.
I am thinking about taking out that audio board from the radio, it is quite awkward to work on it inside the radio, and explore this further.
Any comment on this?

Peter


Attachments:
DfRSoft - Transistor Aging.pdf [180.24 KiB]
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 Post subject: Re: Transistor Question
PostPosted: Jan Sun 14, 2018 6:14 pm 
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Location: Rochester, NY.
Early transistors used point-contact design before the modern and more rugged conventional bipolar junction transistor. The early ones were delicate devices.
Not to say that the point-contact design didn't have advantages, but modern manufacturing techniques has pretty much settled on the BPJ transistor as the norm.
https://en.wikipedia.org/wiki/Point-contact_transistor
We pre-heat the boards before soldering at work as it lessens the thermal shock to the device. Everything is ESD protected throughout the manufacturing process.
Circuit 'transorbs' (TVS diodes) are used to protect junctions from transients and spikes.
https://en.wikipedia.org/wiki/Transient ... sion_diode
Static electricity damage can be latent and show up in the customer's possession, which is bad when lives depend on the equipment. Issues with anything can be intermittent.
They usually either work or they don't.


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 Post subject: Re: Transistor Question
PostPosted: Jan Sun 14, 2018 6:22 pm 
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Location: North of Mpls, Minnesota
fifties wrote:
They can weaken with age. I built a Philmore two Transistor receiver in 1958, which of course used Germanium Transistors. In trying to operate it a few years back, I noticed a distinctive decrease in performance, even after swapping the Electrolytic caps out.
Now exactly what caused the decrease I can't say, but that was the result.

Could it be "hearing loss" :D

Dave


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 Post subject: Re: Transistor Question
PostPosted: Jan Sun 14, 2018 9:29 pm 
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easyrider8 wrote:
fifties wrote:
They can weaken with age. I built a Philmore two Transistor receiver in 1958, which of course used Germanium Transistors. In trying to operate it a few years back, I noticed a distinctive decrease in performance, even after swapping the Electrolytic caps out.
Now exactly what caused the decrease I can't say, but that was the result.

Could it be "hearing loss" :D

Dave

Always a wisenheimer in the crowd...It's usually me though... :wink:

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 Post subject: Re: Transistor Question
PostPosted: Jan Mon 15, 2018 9:59 pm 
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Location: new hyde park ny usa
Thanks for all the useful information! AL


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