AF118 transistor in Leak Stereo 30 - UK Vintage Radio Repair and Restoration Discussion Forum

Studio263 · 5th Jul 2019, 10:34 am

The Leak Stereo 30 amplifier has two AF118 transistors in the driver stages of its power amplifier. The AF118 was designed as a PNP video output transistor for portable TV sets like the Perdio Portarama, and has an unusually high V(c-e) max. of 70V. This is needed in the Leak design because the HT rail is at around 45V, necessary to get a decent output into 15 ohm speakers without the need for transformer coupling.

Normal Germanium transistors can only manage 25 > 32V so cannot be used in this position. I've always got away with my favourite method of removing the transistor and throwing it on the bench as hard as I can 3 times when the 'tin whiskers' problem appears, as well as cutting off the screen lead. It worked with the one that I've been repairing today, but what can one do if it doesn't? Can anyone recommend a suitable alternative for the AF118 in this position?

Restoration73 · 5th Jul 2019, 10:49 am

I first repaired one about 40 years back, even then I ended up using a BC461. I noted
a shortwave radio signal (pick up on speaker leads) was audible - this was cured by
connecting a 1nF disc ceramic across the b-e junction on the copper side. It didn't
affect the audio.
I sometimes need transistors in the TO5,TO39 case style and I use these :
http://www.farnell.com/datasheets/314702.pdf

Argus25 · 5th Jul 2019, 11:33 am

The best replacement for the AF118 is the 2SA358, I have never had one affected by whiskers (unlike the AF118). I have replaced all the AF118's in my germanium TV sets with the 2SA358. They do have unique specs for a germanium, both in the voltage rating and combined high frequency capable department. They also make a very robust output stage for a small AM transmitter.

(I spent some time finding the better replacements for the AF114-to AF117 series, not neglecting the AF118 about 20 years ago when the writing for the demise of this entire series was on the wall and also found that the AF178 or 2N2084 were ideal for the AF114-7 series).

5th Jul 2019, 10:34 am	#1
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,578	AF118 transistor in Leak Stereo 30 The Leak Stereo 30 amplifier has two AF118 transistors in the driver stages of its power amplifier. The AF118 was designed as a PNP video output transistor for portable TV sets like the Perdio Portarama, and has an unusually high V(c-e) max. of 70V. This is needed in the Leak design because the HT rail is at around 45V, necessary to get a decent output into 15 ohm speakers without the need for transformer coupling. Normal Germanium transistors can only manage 25 > 32V so cannot be used in this position. I've always got away with my favourite method of removing the transistor and throwing it on the bench as hard as I can 3 times when the 'tin whiskers' problem appears, as well as cutting off the screen lead. It worked with the one that I've been repairing today, but what can one do if it doesn't? Can anyone recommend a suitable alternative for the AF118 in this position?

5th Jul 2019, 10:49 am	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: AF118 transistor in Leak Stereo 30 I first repaired one about 40 years back, even then I ended up using a BC461. I noted a shortwave radio signal (pick up on speaker leads) was audible - this was cured by connecting a 1nF disc ceramic across the b-e junction on the copper side. It didn't affect the audio. I sometimes need transistors in the TO5,TO39 case style and I use these : http://www.farnell.com/datasheets/314702.pdf Last edited by Restoration73; 5th Jul 2019 at 10:57 am. Reason: Data added

5th Jul 2019, 11:33 am	#3
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: AF118 transistor in Leak Stereo 30 The best replacement for the AF118 is the 2SA358, I have never had one affected by whiskers (unlike the AF118). I have replaced all the AF118's in my germanium TV sets with the 2SA358. They do have unique specs for a germanium, both in the voltage rating and combined high frequency capable department. They also make a very robust output stage for a small AM transmitter. (I spent some time finding the better replacements for the AF114-to AF117 series, not neglecting the AF118 about 20 years ago when the writing for the demise of this entire series was on the wall and also found that the AF178 or 2N2084 were ideal for the AF114-7 series).