AF117 transistors. - UK Vintage Radio Repair and Restoration Discussion Forum

lightning · 3rd Jul 2023, 5:50 pm

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.

G6Tanuki · 3rd Jul 2023, 6:32 pm

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.

Electronpusher0 · 3rd Jul 2023, 6:56 pm

Quite often silicon pnp transistors work as substitutes without changing biasing.
Peter

paulsherwin · 3rd Jul 2023, 7:04 pm

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.

vinrads · 4th Jul 2023, 9:09 am

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.

Craig Sawyers · 4th Jul 2023, 9:29 am

Quote:

Originally Posted by paulsherwin

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

Craig Sawyers · 4th Jul 2023, 9:34 am

Quote:

Originally Posted by vinrads

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

paulsherwin · 4th Jul 2023, 10:02 am

There are lots of threads on this subject here if you search.

Vintage Engr · 4th Jul 2023, 11:10 am

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.

lightning · 4th Jul 2023, 2:05 pm

Okay

Do these old transistors still suffer from "tin whisker" syndrome if they've never been used?

Bazz4CQJ · 4th Jul 2023, 2:07 pm

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

Ian - G4JQT · 4th Jul 2023, 2:07 pm

Quote:

Originally Posted by lightning

Okay

Do these old transistors still suffer from "tin whisker" syndrome if they've never been used?

Yes.

stevehertz · 4th Jul 2023, 7:53 pm

Quote:

Originally Posted by Craig Sawyers

Quote:

Originally Posted by vinrads

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.

Boulevardier · 4th Jul 2023, 8:44 pm

Quote:

Originally Posted by Bazz4CQJ

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!
Mike

G.Castle · 4th Jul 2023, 8:50 pm

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.

agardiner · 4th Jul 2023, 8:53 pm

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.

G.Castle · 4th Jul 2023, 9:02 pm

Quote:

Originally Posted by vinrads

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.

Trevor · 4th Jul 2023, 10:12 pm

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!

paulsherwin · 4th Jul 2023, 10:16 pm

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.

Leon Crampin · 5th Jul 2023, 2:29 pm

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.

3rd Jul 2023, 5:50 pm	#1
lightning Heptode Join Date: Nov 2008 Location: Stockport, Cheshire, UK. Posts: 715	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.

3rd Jul 2023, 6:32 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,015	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. __________________ I'm the Operator of my Pocket Calculator. -Kraftwerk.

3rd Jul 2023, 6:56 pm	#3
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,305	Re: AF117 transistors. Quite often silicon pnp transistors work as substitutes without changing biasing. Peter

3rd Jul 2023, 7:04 pm	#4
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 28,011	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.

4th Jul 2023, 9:09 am	#5
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,767	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.

4th Jul 2023, 10:02 am	#8
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 28,011	Re: AF117 transistors. There are lots of threads on this subject here if you search.

4th Jul 2023, 11:10 am	#9
Vintage Engr Heptode Join Date: Jan 2008 Location: Shrewsbury, Shropshire, UK. Posts: 852	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.

4th Jul 2023, 2:05 pm	#10
lightning Heptode Join Date: Nov 2008 Location: Stockport, Cheshire, UK. Posts: 715	Re: AF117 transistors. Okay Do these old transistors still suffer from "tin whisker" syndrome if they've never been used?

4th Jul 2023, 2:07 pm	#11
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,936	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 __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

4th Jul 2023, 8:50 pm	#15
G.Castle Heptode Join Date: Dec 2020 Location: Swaffham, Norfolk, UK. Posts: 587	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.

4th Jul 2023, 8:53 pm	#16
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,744	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.

4th Jul 2023, 10:12 pm	#18
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	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!

4th Jul 2023, 10:16 pm	#19
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 28,011	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.

5th Jul 2023, 2:29 pm	#20
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	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.