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-   -   Are AF11*'s repairable? (https://www.vintage-radio.net/forum/showthread.php?t=10318)

Radio_Dave 2nd Aug 2006 10:26 am

Are AF11*'s repairable?
 
Hi,

The question's in the title really :)

I was wondering if, somehow, the metal can could be removed and the innards de-whiskered :-)


Thanks
David

Steve_P 2nd Aug 2006 10:34 am

Re: Are AF11*'s repairable?
 
Try charging a cap of about 47uf up to about 50v and discharging it across the pins that have the short circuit.

Usually Screen and one other. This should blow 'em like a fuse.

Cheers,

Steve P

Darren-UK 2nd Aug 2006 10:39 am

Re: Are AF11*'s repairable?
 
I usually do similar to what Steve says above, but twist together collector, emitter and base then discharge between those and the screen lead.

ppppenguin 2nd Aug 2006 10:43 am

Re: Are AF11*'s repairable?
 
I wonder how long it then takes for the whiskers to re-grow.

Radio_Dave 2nd Aug 2006 10:52 am

Re: Are AF11*'s repairable?
 
Yes, I've heard about discharging a capacitor but I was wondering if it's possible to remove the outer casing and remove the whiskers completely? There isn't a vacuum inside a transistor is there???

Thanks
David

GJR 11L 2nd Aug 2006 11:22 am

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Radio_Dave
Yes, I've heard about discharging a capacitor but I was wondering if it's possible to remove the outer casing and remove the whiskers completely?
Thanks
David

You could drill out the innards and hide an AF127/125 or, current favourite here, AF239 inside the can. (Thanks Colin B for turning me on to that alternative).

Blasting with a cap has worked for me, but there's no more work involved in replacing with a new transistor so why bother unpicking it only to have to risk putting it back and finding that the heat from the iron has finished it off for good?
Unless it's from a TR82 type thing whose construction makes this easy and quick.

Snipping the screen lead can effect a cure that can last from a matter of seconds to another few years. I sometimes do that if I'm keeping a set in my collection and can simply fix as required, but for sets that I refurbish to sell, the risk of breakdown is not worth taking so any dodgy AF***s are replaced with brand new equivalents.

Should you choose to drill out the innards of a T07 can, the stuff is very hard indeed and you'll need the device held securely as well as a very sharp drill.

Have fun! ;)

G0PKH - Pete 2nd Aug 2006 11:44 am

Re: Are AF11*'s repairable?
 
I did think It might be possible to unsolder them, and put a sleeve of somekind inside the can to prevent the whiskers from growing again.

Very fiddly if course, and depends if you have anything better to do ;D .

Just musings really.

Pete

Darren-UK 2nd Aug 2006 12:02 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Radio_Dave
Yes, I've heard about discharging a capacitor but I was wondering if it's possible to remove the outer casing and remove the whiskers completely? There isn't a vacuum inside a transistor is there???

Thanks
David

The problem here is that if you remove the can you are for all intents and purposes breaking the connection to the screen lead, thus you are effectively doing the same thing as snipping the screen lead. Also you will likely need heat in order to remove the can and this will likely cause further damage.

I only use the capacitor blast trick if I've no replacements to hand, otherwise I just replace the damn things. There are plenty of dirt-cheap transistor radios at boot sales etc from which you can usually salvage a few usable AF11Xs unless you want to do away with them and use something like an AF127 etc.

Superhet Si 5th Aug 2006 7:24 pm

Re: Are AF11*'s repairable?
 
You might find the capacitor trick carbonises the connection and prevents further growth!
Then again you might not:-/

Tom_I 10th Aug 2006 5:02 pm

Re: Are AF11*'s repairable?
 
I'm sure I've read something recently about someone successfully dismantling an AF117, cleaning out all the old silicone grease, replacing it and reassembling the package, but I can't find it at the moment. If it resurfaces I'll post a link.

Tom

Tom_I 10th Aug 2006 5:07 pm

Re: Are AF11*'s repairable?
 
Yes, here it is from December 2004.

https://www.vintage-radio.net/forum/...ead.php?t=1130

Tom

howard 10th Aug 2006 5:41 pm

Re: Are AF11*'s repairable?
 
Hello,

I reckon around 30% of my radios have AF11* transistors in them so I've bought a load of AF116s very cheap and also AF124s, AF125s, AF126s and AF127s in Germany even cheaper to replace dead or leaky AF11*s. Around 50% of the AF116s even though New Old Stock were shorting out so Ron Bryan very kindly has recycled them all for me by discharging a 47uf cap thru the dud ones, between the screen wire and the other three all soldered together. These are all fine now and are now being used successfully to replace AF116/AF117s :)

Howard :)

af024 10th Aug 2006 8:31 pm

Re: Are AF11*'s repairable?
 
I've done the cap trick but found only something like a 30% success rate. I usually end up with dead shorts round all connections! Mind you, I could be a bit high on the the old volts I suppose.

Tom_I 11th Aug 2006 1:26 pm

Re: Are AF11*'s repairable?
 
1 Attachment(s)
I thought I'd just have a quick go to see how feasible it is to dismantle the can, using a dud example. I held it by the leads and slowly revolved it while applying the soldering iron to the rim of the can. I then braced the can on some newspaper with the iron, gently pulled, and voila!

As you can see, everything is encased in a blob of silicone grease.

I haven't gone any further, as I have errands to run, but I am quite chuffed to have got this far. It remains to be seen whether I have destroyed the thing or not.......:-/

Tom
(Just can't resist trying this sort of thing);)

paulsherwin 11th Aug 2006 1:51 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Tom_I (Post 72622)
I thought I'd just have a quick go to see how feasible it is to dismantle the can, using a dud example. I held it by the leads and slowly revolved it while applying the soldering iron to the rim of the can. I then braced the can on some newspaper with the iron, gently pulled, and voila!

Regardless of what this does to the original AF117, it sounds the best way to stuff an AF125 into an old AF117 can - just remove the can as you have done, insert the AF125, and fill up the case with hot melt glue :D Much better than trying to drill a hole in the bottom.

Paul

Nickthedentist 11th Aug 2006 8:09 pm

Re: Are AF11*'s repairable?
 
That's impressive, Tom:clap:.

Let us know what happens next.

Nick.

Tom_I 12th Aug 2006 7:52 pm

Re: Are AF11*'s repairable?
 
2 Attachment(s)
OK, here's the continuing saga.

The first photo shows the innards after the old silicone grease had been removed. I gave it a quick spray with contact cleaner, but didn't attempt to remove every last vestige of the old grease. I then potted the works in new silicone grease (just ordinary Servisol stuff from Maplins) as shown in the second photo, refitted the can and ran a soldering iron round the rim to tack it all back together.

I don't have any fancy test equipment, but the junctions tested OK with a multimeter. Earlier I described this transistor rather carelessly as "dud". It was internally shorted between the can and one other connection - I forget which. Anyway, it now seemed OK, but to prove the pudding I got out a donor set - an old Murphy Transistor 7 with a wrecked case but working chassis. I removed the most accessible of the AF117's and substituted my repaired one (and I did connect all four leads - no cheating). The set burst into life when I connected a battery, and seemed to work perfectly.

So the answer to David's original question is yes - they can be dismantled and dewhiskered. How long the repair will last is unknown, and whether it's actually worth doing is a matter of opinion.....:-/

I should emphasise that there's nothing original in what I have just done - I'm repeating what has been done before in the post which I mentioned a few messages back. However, it's a good scientific principle to repeat and confirm other people's findings.:thumbsup:

Cheers for now.

Tom

60 oldjohn 12th Aug 2006 9:50 pm

Re: Are AF11*'s repairable?
 
Hi I find that cutting a short section out of the earth lead and replacing the plastic sleeve usually worked for me. Then I read that you should whack it with a screwdriver handle to complete the repair I have not tried It yet. 60 Old John.

Brian R Pateman 13th Aug 2006 9:09 am

Re: Are AF11*'s repairable?
 
An interesting experiment - I wonder if it wil always work?

Certainly one to try next time I come across a shorted AF11*.

Well done and thanks for posting the pictures. It isn't often you get to see "what's in the tin".

Regards,

GJR 11L 13th Aug 2006 8:16 pm

Re: Are AF11*'s repairable?
 
I'm impressed and not a little embarrassed as I've tried getting into these things with a drill before now, never even thinking about using heat. :-]

My method would certainly have wrecked the junctions but even if I end up fitting an AF127/125/239 etc. I will do it this way in future, then there's absolutely nothing to lose and possibly a transistor to preserve.

As Paul said earlier, much better than the drill! :clap:

Nickthedentist 14th Aug 2006 6:16 pm

Re: Are AF11*'s repairable?
 
Great, pictures, Tom.

I'm tempted to have a go myself when the opportunity next arises.

By the way, did you actually see any whiskers?

Nick.

Tom_I 14th Aug 2006 7:23 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Nickthedentist (Post 73187)
By the way, did you actually see any whiskers?

Nick.

No, I can't say I did. I think they are supposed to be very small, though. Did I see 0.008 inches thick somewhere? Anyway, as you can see from the first photo, the old grease was quite opaque compared with the new stuff. It seemed slightly hardened, and most of it came away in one fairly inflexible lump. Also, the short was from the can to one of the other connections, but the shield wire is connected to the metal rim of the bottom part of the device, and the grease didn't reach down that far. The "whisker" must therefore have been to the inner surface of the can itself, and a fair amount of heat had been applied to that to separate the two parts.

If I ever try it again, I'll have a closer look.

Tom

Colin 14th Aug 2006 7:41 pm

Re: Are AF11*'s repairable?
 
I'd have thought the heat would have pretty much done away with the tin whiskers ... I wonder if heating the can (but not to much) would effect a 'cure' ?

Tom_I 14th Aug 2006 8:18 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by stretch289 (Post 73228)
I'd have thought the heat would have pretty much done away with the tin whiskers ... I wonder if heating the can (but not to much) would effect a 'cure' ?

Could well do. I'm beginning to think that I just piled in without thinking too much. Next time I find a shorted AF11* I'll try heating the can without dismantling it, and see if the short is cured.

But then you can never tell how long a fix like that would last. Nor indeed replacing all the silicone grease.

Tom

Nickthedentist 14th Aug 2006 8:26 pm

Re: Are AF11*'s repairable?
 
Does the can need to be hermetically sealed again after repair?

Surely it must have been done for a reason, but leaving it unsoldered would surely make subsequent repairs easier.

And what was the exact purpose of the silicone grease? Damping against microphony, maybe?

Nick.

Radio_Dave 15th Aug 2006 12:45 pm

Re: Are AF11*'s repairable?
 
Unfortunately, since I started this thread I haven't had any faulty transistors to play with!

I've had an idea to drill a couple of small holes into the airspace and inject an acid of some sort. Hopefully the silicone grease would protect the important parts but the whiskers would disolve... Hmm, sounds too simple to work though:D

Regards
David

ppppenguin 15th Aug 2006 12:58 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Radio_Dave (Post 73349)
I've had an idea to drill a couple of small holes into the airspace and inject an acid of some sort. Hopefully the silicone grease would protect the important parts but the whiskers would disolve... Hmm, sounds too simple to work though

Don't like this idea for several reasons. Firstly I suspect that whiskers can grow inside the grease so it just won't work. Secondly you definitely don't want acid residues lurking inside a metal can where it can start eating away at anything. Thirdly, tin is relatively resistant to acid attack so any acid you use to dissolve it will probably do unwanted damage elsewhere.

Radio_Dave 15th Aug 2006 1:15 pm

Re: Are AF11*'s repairable?
 
OK Jeffrey, I guess your right... not one of my better ideas:D. But I might give it a go, one day, when I'm really bored.

Regards
David

Tom_I 22nd Aug 2006 3:20 pm

Re: Are AF11*'s repairable?
 
1 Attachment(s)
A quick update.

Earlier in this thread Nickthedentist asked if I had seen any "whiskers" when dismantling an AF117. I hadn't but now realise that I had got it in mind for some reason that they grew within the silicone grease.:dunce: On re-reading the bit on Paul Stenning's website, they are to be found in the airspace, growing from the inner edge of the can.:-[

Well, I slipped another one apart today, and this time the innards came out leaving the grease in the top of the can. And indeed, with a good magnifying lens you can see them quite clearly. Getting a photo is a different matter. Attached is my best attempt. It's not great, but it is pushing the camera rather beyond its capabilities. Still, you can get some impression of what the whiskers look like in the lower right quadrant, i.e. between 3 and 6 o'clock. There's quite a long one at about half past seven, but I just couldn't get a decent shot of it.

Oh well, better get back to doing something useful.....;)

Tom

paulsherwin 22nd Aug 2006 4:05 pm

Re: Are AF11*'s repairable?
 
You can see the whiskers quite clearly, though the NASA electron microscope gives a better image ;D Interesting.

Paul

Tom_I 22nd Aug 2006 4:51 pm

Re: Are AF11*'s repairable?
 
Yeah, there's an EM in the loft somewhere, but I just couldn't be bothered to get it down.....:D

Tom

Kat Manton 28th Aug 2006 9:17 pm

Re: Are AF11*'s repairable?
 
Hi,

Very interesting thread this.

I wonder if cutting a strip of paper or thin plastic and using it to line the can before reassembly would be an idea? Do the whiskers solely grow in the ungreased space or through the grease as well?

Maybe paint or lacquer inside the can would work..?

I think have a plan... I have a couple of RP18 Sovereigns coming my way. Assuming, as hoped, there are dead AF11x transistors in them I'll take the opportunity to do an experiment. One set can have the transistors zapped with a capacitor and the other I'll dismantle the transistors, clean 'em out then reassemble with a liner or paint inside the can.

As I'm unlikely to part with the sets I'll add a couple of labels inside the sets with details of what I did and when, then see what happens :)

Regards, Kat

paulsherwin 28th Aug 2006 9:28 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Kat Manton (Post 75515)
Do the whiskers solely grow in the ungreased space or through the grease as well?

The NASA analysis showed whiskers growing in both the airspace and silicone grease.

Interesting idea to paint the inside of the can :D I'm not sure all this disassembly in less than clean room conditions will do the junction much good though :-/

Paul

Tom_I 28th Aug 2006 9:50 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Kat Manton (Post 75515)
I wonder if cutting a strip of paper or thin plastic and using it to line the can before reassembly would be an idea? Do the whiskers solely grow in the ungreased space or through the grease as well?

Maybe paint or lacquer inside the can would work..?

These are interesting ideas.

In the AF117 which I tried to photograph, I could only see whiskers in the airspace, but of course I didn't have any sophisticated imaging apparatus. When I re-greased this one I covered all the internal wires. I have only refurbished two examples up until now. They are both working fine, but it's only been a matter of days so far. I guess they need to be monitored for a couple of decades or so to see if the repair is permanent or not.....:-/

And yes, Paul, I do take your point about clean room conditions being rather different from my dining room table. Though I guess these are not the most sensitive of semiconductor devices...;)

Kat, do let us know how you get on. I may just have been lucky so far, but I have found that the cans come apart quite easily.

Regards

Tom

Mike Phelan 29th Aug 2006 8:24 am

Re: Are AF11*'s repairable?
 
I wonder if we just dewhiskered it, cleaned all the siclcone grease out, blobbed some epoxy in the can and stuck the rest of the device back in it, would it be OK?

I suppose the possible problems would be whether the epoxy curing stresses and heat would damage any of the leads or the junction, and whether its insulation would be OK after the heat from soldering or operation in use.

It ought to stop the whiskers forming. and seal the can, if it works.

As I seemed to have a breeding pile of Hackers here, I might try this approach, unless someone comes up with a valid reason that I would be wasting my time. :o

howard 29th Aug 2006 9:11 am

Re: Are AF11*'s repairable?
 
Hello,

I have almost completed the restoration of a Murphy B801 which has 3 x AF117s. Two of the AF117s were dead and I have replaced them with 2 x AF116s, both of which were NOS but had the whiskers problem. These replacement transistors have had a capacitor discharged through them to clear the 'whiskers' (a somewhat simpler solution than dismantling them) and the set works well for around 10 mins but then it starts to distort :( I don't know yet what is causing this problem but I will keep you posted. I hope that this little Murphy will eventually appear in Success Stories with the two 'repaired' AF11*s still in it.

Howard :)

Colin 29th Aug 2006 9:59 am

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by Mike Phelan (Post 75581)
I wonder if we just dewhiskered it, cleaned all the siclcone grease out, blobbed some epoxy in the can and stuck the rest of the device back in it, would it be OK?

I suppose the possible problems would be whether the epoxy curing stresses and heat would damage any of the leads or the junction, and whether its insulation would be OK after the heat from soldering or operation in use.

What about using some form of 'potting compound' ? :shrug: That's effectivley what you're doing to the transistor and it'll probably seal the can back in place too.

arjoll 29th Aug 2006 10:12 am

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by stretch289 (Post 75596)
What about using some form of 'potting compound' ? :shrug: That's effectivley what you're doing to the transistor and it'll probably seal the can back in place too.

I remember pulling various TO3 transistors apart as a youngster and seeing silicon grease in there as well - I thought it was to help conduct heat away from the junction to the case. Will expoxy or a potting compound be as good in this regard?

Colin 29th Aug 2006 10:28 am

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by arjoll (Post 75599)
I remember pulling various TO3 transistors apart as a youngster and seeing silicon grease in there as well - I thought it was to help conduct heat away from the junction to the case. Will expoxy or a potting compound be as good in this regard?

Good point ... there was probably a reason for them being put together the way they were.

Brian R Pateman 4th Sep 2006 2:33 pm

Re: Are AF11*'s repairable?
 
Quote:

Originally Posted by stretch289 (Post 75596)
What about using some form of 'potting compound' ? :shrug: That's effectivley what you're doing to the transistor and it'll probably seal the can back in place too.

Potting Compounds tend to generate a fair bit of heat in curing. This is not a problem for most applications but I'm not so sure if this would be the case in this application. The heat would be quite concentrated on the junction and might alter the characteristics. This might not be a problem in most of the AF11* situations but is worth considering.

Regards,

Superhet Si 7th Sep 2006 10:20 pm

Re: Are AF11*'s repairable?
 
You could try araldite as this sets quickly and with little heat generation.
It also conducts heat fairly well and the junctions of the transistor will push through the low viscosity of the freshly mixed glue. Yummy!!

Kat Manton 17th Oct 2006 9:19 pm

Re: Are AF11*'s repairable?
 
Hi,

My dead AF11x collection seems to have increased with the addition of Hackers RP30, RP35 and yet another RP18 to the collection, none doing anything other than going "plop" at switch-on.

Watch this space for results of a bulk AF11x resurrection session, coming soon... ;)

Regards, Kat

Kat Manton 21st Oct 2006 10:04 am

Re: Are AF11*'s repairable?
 
Hi,

I've just been reading a new item on the NASA Goddard Space Flight Center Tin Whisker (and Other Metal Whisker) Homepage, specifically "Evaluation of Conformal Coatings as a Tin Whisker Mitigation Strategy, Part 2".

It seems the whiskers managed to penetrate the various coatings tested.

Fascinating stuff. But, going by that research, it looks like coating the inside of our transistor cans will merely slow whisker growth down a bit.

Regards, Kat

Kat Manton 21st Oct 2006 2:28 pm

Re: Are AF11*'s repairable?
 
Hi again,

I've made a start.

The victi... research subject in question: One red Hacker RP30 Herald, serial 67656. Found to have an oscillator which didn't, cause... you guessed.

I decided to take the transistor apart, but it proved somewhat recalcitrant. I'd definitely got it hot enough to melt the solder, only the 'lid' seemed to be on tight. Eventually I gave up, thinking I'd probably destroyed it anyway.

Once it'd cooled off, just out of curiosity I checked it anyway. My meter claimed there was still a couple of diode junctions inside and there was no leakage from anything to the screen lead. So I tacked it temporarily on the back of the board and... one working Herald. I've since fitted it properly and I'm sat listening to it as I type this.

So, heating the case up melts the whiskers; not exactly unexpected. I'll make a note of what I've done and when and pop it inside the radio. Let's see how long this lasts... :)

Regards, Kat.

PJL 8th Nov 2006 1:02 am

Re: Are AF11*'s repairable?
 
Tried this with the transistor in circuit just placed the soldering iron on the top of the can, waited till the solder on the rim was melted and cooled with a damp cloth...can't get much simpler than this..Peter

G0PKH - Pete 8th Nov 2006 9:51 am

Re: Are AF11*'s repairable?
 
Quote:

I decided to take the transistor apart, but it proved somewhat recalcitrant. I'd definitely got it hot enough to melt the solder, only the 'lid' seemed to be on tight. Eventually I gave up
I have also noticed this, the very first Hacker that I restored (an RP18)also had transistors that I simply could not get apart. I even tried with a mini gas blowtorch 8-o .

However like Kat, I thought I may as well test them before binning, and was shocked to find they actually worked.
Even after 2 years, the set still performs wonderfully.

I have another RP18 that I am restoring for a friend, so I will try this first before struggling to remove the transistors.

GJR 11L 8th Nov 2006 10:34 am

Re: Are AF11*'s repairable?
 
This idea casts a very different light on the viability and therefore the chances of survival of more than a dozen sets in my little collection alone.

I have now tried the soldering iron on the can technique with no fewer than eight AF11*s and have achieved the desired result in every case! Remind me, what was all that heatsink, in & out in a second, don't let Ge devices get hot, all about?!

I can only wait and see how long-term reliability pans out, but at this rate, I'll be able to turn my pile of AF127s and 125s into spending money for Christmas! :beer: :thumbsup:

PJL 8th Nov 2006 7:36 pm

Re: Are AF11*'s repairable?
 
My guess is there are a couple of reasons why this works:
1. the heat is applied to the can which is insulated from the Ge and is only applied for a short time and cooled down quickly.
2. there is a big blob of silicon grease over the Ge with a high thermal capacity which prevents the Ge temperature rsing too quickly.

Even so I turned on a radio immediately after cooloing and it was dead presumably from chronic leakage but gradually recovered as it internally cooled.

G0PKH - Pete 9th Nov 2006 6:36 pm

Re: Are AF11*'s repairable?
 
Well,

The Hacker Sovereign RP18 I was repairing for a friend now works, all 4 AF114's responded well to the treatment. Once I had replaced the diodes in the ratio detector, it sounded even better, one had gone leaky, and I couldn't balance it.

This technique certainly seems to work, for how long we can't be sure.
Even better was the fact that I performed the act with the transistors in circuit. They are a :censored: to remove in the RP18.

Pete


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