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Old 3rd Jul 2023, 5:50 pm   #1
lightning
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Default AF117 transistors.

Wanted

Two good AF117's for one of my radios, if such a thing exists. Can you still get these in working order?

Or if not, an alternative that will work.
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Old 3rd Jul 2023, 6:32 pm   #2
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Default Re: AF117 transistors.

AF11x transistors - even unused 'new old stock' - get the tin-whisker failure.

Don't bother seeking replacement AF11x transistors, even if they work now they'll likely fail in the future.

AF12x series transistors seem less-susceptible to the whisker-plague, and if you *must* stick with Germanium are a good path; but to be honest, with a bit of bias-fiddling there are loads of cheap-and-cheerful Silicon transistors that can be subbed and will be a lot more reliable in the long term.
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Old 3rd Jul 2023, 6:56 pm   #3
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Default Re: AF117 transistors.

Quite often silicon pnp transistors work as substitutes without changing biasing.
Peter
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Old 3rd Jul 2023, 7:04 pm   #4
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Default Re: AF117 transistors.

Indeed, it's always worth popping in a BC214 or something similar and seeing what happens. They're usually fine.

I agree that buying NOS AF11x transistors is a mistake. The AF12x series are the closest replacements, but are getting pricey now and lots of alternatives will be fine.
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Old 4th Jul 2023, 9:09 am   #5
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Default Re: AF117 transistors.

I have loads of new old stock AF117's etc. Has anyone tried flushing the innards out a couple of small holes drilled near the top? Should do the trick, I may give it a try.

Mick.
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Old 4th Jul 2023, 9:29 am   #6
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Default Re: AF117 transistors.

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Originally Posted by paulsherwin View Post
Indeed, it's always worth popping in a BC214 or something similar and seeing what happens. They're usually fine.

I agree that buying NOS AF11x transistors is a mistake. The AF12x series are the closest replacements, but are getting pricey now and lots of alternatives will be fine.
Langrex have AF124 at £12 for five. They have 40-odd left in stock.

Craig
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Old 4th Jul 2023, 9:34 am   #7
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Default Re: AF117 transistors.

Quote:
Originally Posted by vinrads View Post
I have loads of new old stock AF117's etc. Has anyone tried flushing the innards out a couple of small holes drilled near the top? Should do the trick, I may give it a try.

Mick.
There are methods of blowing the tin whiskers away. I'd have to look up the method (I just searched the web on this), but I think it involves shorting ebc and discharging a capacitor between the shorted ebc and screen wire.

You'd have to have to look up the precise conditions, capacitor value and voltage.

Craig
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Old 4th Jul 2023, 10:02 am   #8
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Default Re: AF117 transistors.

There are lots of threads on this subject here if you search.
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Old 4th Jul 2023, 11:10 am   #9
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Default Re: AF117 transistors.

BF450's usually work, with no bias adjustment. It depends on the circuit, but I've used them in Bush, Roberts & Hacker with no problems.

David.
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Old 4th Jul 2023, 2:05 pm   #10
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Default Re: AF117 transistors.

Okay

Do these old transistors still suffer from "tin whisker" syndrome if they've never been used?
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Old 4th Jul 2023, 2:07 pm   #11
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Default Re: AF117 transistors.

I wouldn't try "liquid flushing", but I'm sure Craig is right, that people have successfully zapped the whiskers. How long they would go before the problem could come back .

B
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Old 4th Jul 2023, 2:07 pm   #12
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Default Re: AF117 transistors.

Quote:
Originally Posted by lightning View Post
Okay

Do these old transistors still suffer from "tin whisker" syndrome if they've never been used?
Yes.
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Old 4th Jul 2023, 7:53 pm   #13
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Default Re: AF117 transistors.

Quote:
Originally Posted by Craig Sawyers View Post
Quote:
Originally Posted by vinrads View Post
I have loads of new old stock AF117's etc. Has anyone tried flushing the innards out a couple of small holes drilled near the top? Should do the trick, I may give it a try.

Mick.
There are methods of blowing the tin whiskers away. I'd have to look up the method (I just searched the web on this), but I think it involves shorting ebc and discharging a capacitor between the shorted ebc and screen wire.

You'd have to have to look up the precise conditions, capacitor value and voltage.

Craig
I've just banged them before now with success. Bang them against a hard surface to dislodge the hair-like tin whiskers.
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Old 4th Jul 2023, 8:44 pm   #14
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Default Re: AF117 transistors.

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Originally Posted by Bazz4CQJ View Post
I'm sure Craig is right, that people have successfully zapped the whiskers. How long they would go before the problem could come back .

B

I "zapped" the AFxxx transistors on a 1960s Beolit 15 years ago, and it's still going strong!
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Old 4th Jul 2023, 8:50 pm   #15
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Default Re: AF117 transistors.

This is the method of zapping whiskers I've used, it has never failed me yet:
https://www.markhennessy.co.uk/artic...ransistors.htm

There has been suggestions made to me that ''Made in Holland' and 'Made in the USA' (BEL) transistors of this type don't suffer from tin whiskers as much as 'Made in Great Britain' marked ones, perhaps the plating on the cases of the Mullard ones was pure Tin, or possibly the application of protective putty to stop moisture contamination of the germanium was applied differently?

I don't think I've ever come across one of these that has actually failed as a transistor, it's always been the whiskers!

The glass S02 cased germanium was always the better package.
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Old 4th Jul 2023, 8:53 pm   #16
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Default Re: AF117 transistors.

I used to zap the whiskers away, and hadn't had a set back in over 10 years. However, there is no doubt that the problem is getting worse overall. Zapping the whiskers between the can and transistor junction is fine, but I reckon I have had transistors with whiskers starting to form between the actual junction points. They show up on my transistor analyser as the device reading as 2 diodes, instead of a transistor.

I would still be happy to zap them for my own radios, but for customers I do now replace them.
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Old 4th Jul 2023, 9:02 pm   #17
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Default Re: AF117 transistors.

Quote:
Originally Posted by vinrads View Post
I have loads of new old stock AF117's etc. Has anyone tried flushing the innards out a couple of small holes drilled near the top? Should do the trick, I may give it a try.

Mick.
Germanium dissolves at low temperatures and is ruined by moisture so I wouldn't try flushing! I have never done it but I have read that it is possible to pop the bottom glass seal and clean out the case! Either to refit the original or restuff with alternative guts.

Last resort stuff.
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Old 4th Jul 2023, 10:12 pm   #18
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Default Re: AF117 transistors.

I have in the past unsoldered the case soldering iron on the base and pull the can off
clean out the crap and put them back together some worked some did not!
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Old 4th Jul 2023, 10:16 pm   #19
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Default Re: AF117 transistors.

There are lots of dodges, but the plain fact is that AF11x transistors have very poor long term reliability. It's worrying that other 1960s Mullard transistors seem to be developing internal shorts too.
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Old 5th Jul 2023, 2:29 pm   #20
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Default Re: AF117 transistors.

I think the critical factor is the case plating material. In the case of the AF11x series and some of the output stage devices such as the AC128, the plating is tin - which forms whiskers on the inside of the casn, with fatal results.

Conversely, the nickel plating used on most TO-18 cans never seems to cause this problem.

Having evicted no end of AF117 devices, I had my first AC187 failure due to whiskering the other day - fitted to a Grundig portable. As these seem to fail far less frequently than the AF11x series, I have to confess that I just replaced it with the same device - matched for hfe at around the quiescent current. All now OK.

Leon.
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