The Pot's whiskers

[unitelex]

Discovered some significant tin whiskers outside and inside the volume pot of a Wartime Civilian Receiver, which it has been growing for 75 years. The longest one measures 10 to 11mm in length, suggesting an average growth rate of 0.13 mm/year in air.

Needless to say it was giving trouble, intermittently shorting the signal

[vinrads]

Wow! that is something to look out for , thanks for the excellent pictures , Mick.

[G6Tanuki]

Fascinating! But, to quote Tom Jones, "It's not unusual". I had similar issues with the volume-control in my WWII-vintage PCR communications-receiver [built by Philips]. Crackles and random comings-and-goings of the audio. The whiskers had grown from the plated steel shell of the control to touch the carbon track.

[Boulevardier]

Originally Posted by G6Tanuki

The whiskers had grown from the plated steel shell of the control to touch the carbon track.

Bur were these tin whiskers?

Mike

[Nickthedentist]

Reminded me of this (and several other) threads here: https://www.vintage-radio.net/forum/...d.php?t=118293

[G6Tanuki]

Originally Posted by Boulevardier

Bur were these tin whiskers?

Mike

I guess it was tin-plating on the steel shell [the shell had tabs that were crimped over to retain the Bakelite potentiometer body; I don;t think you could have crimped that if it was solid tin, it would have been too brittle]

[Buzby123]

Wow !.

I've known of tin whiskers for ages, but (a) have never knowingly come across one, and (b) never realised how widespread and dangerous they are.

This NASA page shows a tin whisker from a diode that led to the shutdown of a reactor in a nuclear power station. https://nepp.nasa.gov/whisker/photos/index.html#diode

This page documents a failure due to whiskers on a DIL IC package. https://nepp.nasa.gov/whisker/anecdo...ear/index.html

I also didn't know that Zinc also makes whiskers.

Scary stuff !

[Julesomega]

Even copper does The Bus Rails and Bus Bars sections of the NASA whiskers pages show catastrophic failures of LV (500V ac) power distribution systems

I'm amazed that our house power has remained on long enough for me to post a quick reply. I'd expect to be seeing 'whisker' faults occurring all around me, but maybe they are: I recently posted about a DAB radio that had become unusable but which sprung back into life after unplugging and re-plugging some fine-pitch board interconnect cables. Whiskers from lead-free solder could account for this

[Red to black]

I have never seen Copper whiskers ever, could you please show a link for that ? TIA

[Julesomega]

The text is all about tin-plated copper, but the pictures look like bare copper to me
https://nepp.nasa.gov/whisker/anecdo...bar/index.html

[Red to black]

Thanks for that Jules, I can honestly say I have never come across that before, a new one on me

[Refugee]

Originally Posted by Boulevardier

Bur were these tin whiskers?

Mike

They could be zinc whiskers.
Zinc whiskers have got a reputation for causing computer errors.
https://dataspan.com/blog/what-are-z...-data-centers/

[Boulevardier]

Wonder if there's been any systematic investigation of which metals can grow whiskers and which can't...

Mike

[Sideband]

I came across a similar thing in a Philips Superinductance radio where whiskers had grown from a tin-plate screen. I was unfamiliar with the 'tin whisker' problem then (some 25 years ago) and wish I had kept the photos.

[CambridgeWorks]

The link in post 10, centre picture shows them growing out at an angle. That is exactly the way I used to see them on tin plated metal screens as used on rf modules.
Longest I ever saw was about 6mm on a screen about 15 to 18 years old. Just visible with the naked eye. Breathing near them made them wobble around a bit.
Rob

[ms660]

Tin, Zinc, Cadmium....Filamentry Growths on Metal Surfaces (Compton) circa 1951:

https://hlinstruments.com/RoHS_artic...es-Whisker.pdf

Lawrence.

[Refugee]

I have found them in a Marconi signal gererater around the mechanical components behind the picture frame front panel.

[Boulevardier]

Originally Posted by ms660

Tin, Zinc, Cadmium....Filamentry Growths on Metal Surfaces (Compton) circa 1951:

https://hlinstruments.com/RoHS_artic...es-Whisker.pdf

Lawrence.

Thanks Lawrence - most interesting!
Mike

[duncanlowe]

I found out about whiskers during an interview. I'd never heard of them before. The interviewer reccomended a site to read about them.

I spite of that I got offered the job, and was about to take it when I found the department was moving offices as I was working my notice, and would have added 40 minutes on to the hour commute I was expecting.

[McMurdo]

In the case of my whiskered volume control, I think a whisker was acting as a coherer, ie shorting to earth following a local RF spike and then clearing with a light tap. Exactly how marconi's morse system worked.