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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 2nd Aug 2006, 9:26 am   #1
Radio_Dave
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Default 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
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Old 2nd Aug 2006, 9:34 am   #2
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Default 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
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Old 2nd Aug 2006, 9:39 am   #3
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Default 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.
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Old 2nd Aug 2006, 9:43 am   #4
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Default Re: Are AF11*'s repairable?

I wonder how long it then takes for the whiskers to re-grow.
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Old 2nd Aug 2006, 9:52 am   #5
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Default 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
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Old 2nd Aug 2006, 10:22 am   #6
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Default 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!
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Old 2nd Aug 2006, 10:44 am   #7
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Default 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 .

Just musings really.

Pete
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Old 2nd Aug 2006, 11:02 am   #8
Darren-UK
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Default 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.
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Old 5th Aug 2006, 6:24 pm   #9
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Default Re: Are AF11*'s repairable?

You might find the capacitor trick carbonises the connection and prevents further growth!
Then again you might not
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Old 10th Aug 2006, 4:02 pm   #10
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Default 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
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Old 10th Aug 2006, 4:07 pm   #11
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Default Re: Are AF11*'s repairable?

Yes, here it is from December 2004.

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

Tom
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Old 10th Aug 2006, 4:41 pm   #12
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Default 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

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Old 10th Aug 2006, 7:31 pm   #13
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Default 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.
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Old 11th Aug 2006, 12:26 pm   #14
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Default Re: Are AF11*'s repairable?

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)
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Old 11th Aug 2006, 12:51 pm   #15
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Default Re: Are AF11*'s repairable?

Quote:
Originally Posted by Tom_I View Post
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 Much better than trying to drill a hole in the bottom.

Paul
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Old 11th Aug 2006, 7:09 pm   #16
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Default Re: Are AF11*'s repairable?

That's impressive, Tom.

Let us know what happens next.

Nick.
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Old 12th Aug 2006, 6:52 pm   #17
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Default Re: Are AF11*'s repairable?

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.

Cheers for now.

Tom
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Old 12th Aug 2006, 8:50 pm   #18
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Default 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.
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Old 13th Aug 2006, 8:09 am   #19
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Default 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,
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Old 13th Aug 2006, 7:16 pm   #20
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Default 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!
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