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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 19th Jul 2019, 7:06 pm   #1
poppydog
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Default Tired diode

What is meant by the term "one of the diodes is getting tired "? It's in the repair and restoration section of this site.

https://www.vintage-radio.com/repair...ltfinding.html

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Old 19th Jul 2019, 7:22 pm   #2
ms660
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Default Re: Tired diode

I would say the diodes internal contact point (possibly the "whisker") has gone to sleep, eg: not making full electrical contact, as well as others it used to happen in some of the Bush transistor radios where it was located inside the last IFT can.....Google Images...point contact diode to see the internal arrangement.

Lawrence.

Last edited by ms660; 19th Jul 2019 at 7:31 pm. Reason: addition
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Old 19th Jul 2019, 8:21 pm   #3
poppydog
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Default Re: Tired diode

Thanks for that Lawrence, I had never heard of a tired diode and could find no info on it. Also never heard of a whisker that has gone to sleep (I've heard of wood that's "gone sleep") either.

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Old 19th Jul 2019, 8:37 pm   #4
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Default Re: Tired diode

Not specifically a tired whisker as such.

Where the whisker contacts the diode material, that contact point sometimes goes high resistance for whatever reason, we would call that a tired diode, also we used the same term with fuses, a tired fuse or sometimes a lazy fuse.

Lawrence.
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Old 19th Jul 2019, 9:50 pm   #5
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Default Re: Tired diode

With a valve diode it could relate to low emission. In either case it basically means the diode is working properly....
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Old 20th Jul 2019, 7:07 pm   #6
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Default Re: Tired diode

Regard it as a figure of speech, in the same way as a radio which has great difficulty of bringing in stations might be described as being deaf. Personification of an inanimate object, it has no ears so cannot be literally deaf...
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Old 20th Jul 2019, 8:24 pm   #7
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Default Re: Tired diode

Some would say you shouldn't say a radio is deaf -- it's insensitive .....

(Oh, alright, I'll get my coat .....)
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Old 20th Jul 2019, 9:22 pm   #8
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Default Re: Tired diode

I had not heard of a tired diode before, I know sheltered life, if the the diode of whatever type was not up to spec in any way I just said faulty.
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Old 21st Jul 2019, 12:39 am   #9
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Default Re: Tired diode

Selenium rectifiers smell off when they get past their use by dates
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Old 21st Jul 2019, 12:49 pm   #10
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Default Re: Tired diode

The context is an FM detector, needing reasonably well balanced diodes. More commonly associated with valves such as the *ABC80, but a possibility with a semiconductor. There can be a surprisingly high voltage here with a strong signal, particularly on AM.
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Old 21st Jul 2019, 2:11 pm   #11
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Default Re: Tired diode

The PIV of diode needed will be at least the peak-peak voltage of the AC signal.

OA81s are getting pretty leaky (>100uA) by 75v
Common '2800' small signal schottkys are rated to 70v, but beware of anonymous ones - some were as low as 4v rating (very low threshold and low-C, though)

Current limited over-voltage events can be survived by diodes, but sometimes with progressive degradation leading to eventual failure.

'Tired' isn't actually a bad term for it.

David
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Old 21st Jul 2019, 4:02 pm   #12
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Default Re: Tired diode

'Tired' is also a colloquial description of a component meaning more or less the same as 'a bit knackered' - a component that is still working but performing poorly.
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