AF12x Transistor failure - UK Vintage Radio Repair and Restoration Discussion Forum

'LIVEWIRE?' · 7th Apr 2015, 7:03 pm

As most members will know, the AF12x series transistors are usually very reliable. However, the mixer transistor (AF126 in a vintage Philips Car radio model N5X34T) had failed so that the resistance between the base and emitter of the device is ca. 95 ohms both ways round. I can't say that I've ever known an AF12x transistor to fail before

HamishBoxer · 7th Apr 2015, 7:38 pm

Well as they say there is always a first time.If the components are ok around that stage it is possibly just a one off.

paulsherwin · 7th Apr 2015, 7:42 pm

Interesting and a useful alarm call. Presumably this is a junction failure rather than the AF11x tin whisker problem. Let's hope so.

HamishBoxer · 7th Apr 2015, 8:10 pm

Good point Paul. I was not even thinking about the dreaded whisker problem.

ukcol · 7th Apr 2015, 8:25 pm

I have always assumed (rightly or wrongly) that the AF12x types use a different material for the case to that of the AF11x types. That being the case (excuse the pun) it won't be tin whiskers but just a one-off random failure.

Sideband · 7th Apr 2015, 8:35 pm

Lets be honest...any transistor can fail even seemingly totally reliable ones. AF12x transistors must be getting on for 50 years old by now so well past their design life. If it is tin whisker, you'll be able to measure a resistance between the case and one or more electrodes.

'LIVEWIRE?' · 8th Apr 2015, 9:01 am

The transistor in question is original to the radio, which must be around 50 years old by now. There are 4 other AF12x transistors in it, all of which check out OK, plus 3 x AC12x types, but the only othe failed components were the AGC Diode (replaced by me with an AA119),which was O/C, and a very leaky main smoothing capacitor.

7th Apr 2015, 7:03 pm	#1
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	AF12x Transistor failure As most members will know, the AF12x series transistors are usually very reliable. However, the mixer transistor (AF126 in a vintage Philips Car radio model N5X34T) had failed so that the resistance between the base and emitter of the device is ca. 95 ohms both ways round. I can't say that I've ever known an AF12x transistor to fail before

7th Apr 2015, 7:38 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: AF12x Transistor failure Well as they say there is always a first time.If the components are ok around that stage it is possibly just a one off. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

7th Apr 2015, 7:42 pm	#3
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,968	Re: AF12x Transistor failure Interesting and a useful alarm call. Presumably this is a junction failure rather than the AF11x tin whisker problem. Let's hope so.

7th Apr 2015, 8:10 pm	#4
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: AF12x Transistor failure Good point Paul. I was not even thinking about the dreaded whisker problem. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

7th Apr 2015, 8:25 pm	#5
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: AF12x Transistor failure I have always assumed (rightly or wrongly) that the AF12x types use a different material for the case to that of the AF11x types. That being the case (excuse the pun) it won't be tin whiskers but just a one-off random failure.

7th Apr 2015, 8:35 pm	#6
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,578	Re: AF12x Transistor failure Lets be honest...any transistor can fail even seemingly totally reliable ones. AF12x transistors must be getting on for 50 years old by now so well past their design life. If it is tin whisker, you'll be able to measure a resistance between the case and one or more electrodes. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

8th Apr 2015, 9:01 am	#7
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: AF12x Transistor failure The transistor in question is original to the radio, which must be around 50 years old by now. There are 4 other AF12x transistors in it, all of which check out OK, plus 3 x AC12x types, but the only othe failed components were the AGC Diode (replaced by me with an AA119),which was O/C, and a very leaky main smoothing capacitor.