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One Thing Leads To Another


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Hi Folks,

Do you remember the very old advert from the 60's when the teenage son shouts out " Dad, I've got a whisker"  Shaving advert I think.

 

Well, read on - but first a warning - we will be going into nerd mode.

15 years ago I installed leccy windows in my 4A (see other thread)

September 2020 I started work on one of the motors that stopped working long ago.

The motor needed a switch. The switch needed somewhere to go

I modified the Dash central support to take extra switches.

In modifying and repairing the central support I had to repair the hole where the radio goes - That's when I ended up with a TIG welding machine.

I needed a 1960's style radio to go in the new hole that was made.

A friend (we'll call him Stuart for example) sent me one that had been living in a cupboard for some time.

It was dead :o  but may not have been when put in the cupboard - old transistors are funny things.  (Remember - Dad I've got a whisker)

WARNING WARNING WARNING this is where it gets nerdy

I took the lid off the radio and thought - where the hell do I start.

I stuck my finger on the volume control and it buzzed - good so the audio is working  ( do not do this on mains radios)

Many many moons ago I read in 'Practical Television' magazine that certain transistors could for an unknown reason go dead due to two of their legs becoming entwined:wub:

I had three transistors with the grand title of AF117. When they were first made they were stunning little devices. 60 years on they are sh*te.

The active part of the TRanny is in a little metal Tin can to keep it quiet. The inside of this can is tin coated (Tin can - get itB))

In the early 70's NASA (yes the rocket people) found that the inside Tin coating was growing whiskers  (remember the opening line above).

Eventually the whiskers could touch the active bit in the centre. This grounded the active bit and immediately stopped it working :o  Not good for rockets.

The next bit is science fiction fact. To remove the whisker you charge up a capacitor (1000uf x 65V) and short this across all of the legs in a particular fashion.

In theory this will burn the whisker off. In practice it does exactly that.

Anyway, only one of the TRannies had a whisker. I put them all back into the circuit. Turned it ON, Dead. Bu99er.

So in desperation I contacted another friend (I'll call him Bob) and asked if he had enough knowledge to see what was going on. He did - yippee.

A couple of days later he called to say it was all done and working.:)  It turned out that two of the three TRannies that I tested and found good had become bad in taking out and replacing back into the PCB. The burning off only affects those whiskers that are touching. However new whiskers can short immediately afterwards.

So what has been learnt. Do NOT under any circumstances start a project. It will get out of hand and involve many people.

The second thing - do not buy/beg/steal or borrow old TRanny radios as the little transistors have minds of their own and will TRick you at every twist and turn.

The third thing - the Radiomobile 1080 looks spot on in the dash central support.

 

What a journey

Roger

 

 

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Germanium transistors do not like like too much heat, I'm wondering if in taking them out, & putting back in you may have damaged them while soldering.

It used to be best practice to grip their legs (one at a time) above the circuit board with a pair of thin nose pliers to take the heat away when soldering. That would not be possible in your case because there would have been no room to do that. Make the soldering quick & spray freezer on the tranny immediatly after is one way to do it..

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The AF series transistors are notorious for doing that. Unfortunately being PNP germanium types you can't always just replace them with a better silicon transistor.  Sometimes you would have to change the bias resistors too. 

https://nepp.nasa.gov/whisker/anecdote/af114-transistor/2005-Brusse-tin-whiskers-AF114-transistors.pdf

The tin-whisker thing is a problem for undersea  cables. The early telephone cables  needed vacuum-tube repeater amplifiers at intervals along the cable to compensate for signal losses, and which had to work under great pressure so were solidly constructed and of course plated internally to prevent corrosion.  It was found that in the cold undisturbed depths,  the whiskers grew in the cases and connectors until the amplifiers stopped working when things became shorted out.  It was a very expensive exercise to dredge up the cable so the amplifier could be replaced.

It is still a problem even now:

https://www.subseauk.com/documents/presentations/neil_douglas_-_viper_subsea_-_innovative_engineering_products.pdf 

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Well I did say I couldnt guarantee it and it has been stored in a fairly unsuitable environment since the early 90`s

Well done for getting it working though.

Stuart.

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Hi Stuart,

as I mentioned - it probably was working when it went into the cupboard.

These transistor are very very iffy.  You can buy them on ebay for quite a sum but they will still be 60 years old, there about's.  No guarantee of working.

I have a Hacker Harrier radio and it is a cracker. But after two years in a cupboard it did not work. Exactly the same problem The screen wire had whiskered tot he collector.

 

Roger

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All this confirms for me I did the right thing and threw my original Phillips transistor car radio away.  
Stupid thing was never on station and the fitting in a side screen TR was a clumsy clutter of brackets and wire.  My brother got clever and fitted his in the glove box with door mounted speakers.  Not for me.


Oh, and it was inaudible above 30 mph once the roof is off. 

Bin it and concentrate on the driving experience.

 

Peter W

 

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If you want the vintage look, but wish for better quality of sound or even your own music the old sets can easily be modified to allow connection to ipod / mobile phone etc, either by cable, or bluetooth.

Bob.

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Hi Bob,

that is in the back of my mind. If it really irks me then I may well go that way.

 

Hi Pete,

I really want the 'look'. I appreciate the sound will be way off TRack. But when I'm laid up in a car park eating the local cuisine I can here the news,

 

Roger

 

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My blue tooth connected hearing aids give me connectivity to my iPhone.  I can listen to the news, a play, answer a phone call, etc.

 

Less than the price of a set of wire wheels   https://www.costco.co.uk/hearing-aid

Peter W

 

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Solid state has indeed come a long way.  From single clunky bipolar devices to today's microprocessors that can have tens of BILLIONS of MOS transistors in the package.

I've also used the charged capacitor trick to revive shorted NiCad cells, in which case I think it is nickel whiskers.

Ed

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Good for having a go Roger - as we all know you would!

Sick of throwing out so much when items cease to work, for some years I have operated a rule in our house that nothing is disposed of on the basis that is broken / not working until I have attempted to revive it / scavenged potentially useful bits from it. As you know, I am a bear of limited skills. I have had a few success, a few failures and have learnt a few skills along the way and got some great satisfaction from small wins. Not smug; I just think this is the right thing to do.

Miles

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38 minutes ago, MilesA said:

Good for having a go Roger - as we all know you would!

Sick of throwing out so much when items cease to work, for some years I have operated a rule in our house that nothing is disposed of on the basis that is broken / not working until I have attempted to revive it / scavenged potentially useful bits from it. As you know, I am a bear of limited skills. I have had a few success, a few failures and have learnt a few skills along the way and got some great satisfaction from small wins. Not smug; I just think this is the right thing to do.

Miles

Spot on.

 

Roger

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