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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 7th Jul 2007, 9:37 pm   #1
Hybrid tellies
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Default AF117 replacements

I have been told by a good authority that the AF239 transistor is a good replacement for the troublesmome AF117. It seems to be quite readily available as well.
As this transistor can be found in some uhf tv tuners I presume that it could quite happily be a replacement for the range AF114s-AF117s.
All views welcome
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Old 7th Jul 2007, 10:37 pm   #2
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Default Re: AF117 replacements

Have used these before, as I have quite a few, But I have had to do some realignement and the results have not always been satisfactory. Much better to use AF124-AF127 as these require less extra work to be carried out.

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Old 8th Jul 2007, 12:53 am   #3
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Default Re: AF117 replacements

You can use quite a wide range of transistors to replace AF11xs, depending on the circuit, but I agree AF12x types are likely to give fewest problems because they're basically the same transistor in another package.

In many cases it's easy to replace the AF11xs with a transistor socket and experiment with different transistors. You can make a basic transistor socket by cutting up an IC socket with a Dremel or even a junior hacksaw.

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Old 8th Jul 2007, 1:58 am   #4
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Default Re: AF117 replacements

Hi Simon

I've used the AF239 to replace AF114-117's without any great problems in several radio's I've restored. The majority of the time re-alignment has not been necessary, but obviously that depends largely on the specific circuit you are fitting them into
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Old 8th Jul 2007, 12:34 pm   #5
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Default Re: AF117 replacements

Quote:
Originally Posted by Hybrid tellies View Post
I have been told by a good authority that the AF239 transistor is a good replacement for the troublesmome AF117. It seems to be quite readily available as well.
As this transistor can be found in some uhf tv tuners I presume that it could quite happily be a replacement for the range AF114s-AF117s.
All views welcome
Although listed as an equivalent for the AF11x series, I certainly wouldn't recommend the AF239. I tried using the 239 as a replacement long ago and met with poor results. In fact if fitted in mixer/oscillator stages the 239 wouldn't even oscillate. The reason is obvious: the AF239 has a typical hfe of just 10, whereas the AF11x series have MINIMUM hfe's of 50.

Best stick to AF12x, particularly if repairing a Mullard module. Anyone feeling adventurous could try using the BF450. This is a silicon pnp RF device with a minimum hfe of, yes, 50. It will often work as a direct replacement without modifying the biassing.

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Old 8th Jul 2007, 1:03 pm   #6
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Default Re: AF117 replacements

If you want AF11X series, I think Birkett in Lincoln still has some at about 75p.
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Old 8th Jul 2007, 6:37 pm   #7
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Default Re: AF117 replacements

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If you want AF11X series, I think Birkett in Lincoln still has some at about 75p.
Jim
Sycom in Leatherhead still stock Mullard AF116s for 50p each but expect 50% of any NOS AF11* to be duds.

I bought all my stock of NOS AF12* transistors which I always use to replace AF11*, in Germany and Denmark when they were cheap but they're not cheap now ... keep an eye on eBay though cos they often turn up there.

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Old 8th Jul 2007, 8:21 pm   #8
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Default Re: AF117 replacements

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Sycom in Leatherhead still stock Mullard AF116s for 50p each but expect 50% of any NOS AF11* to be duds.
Indeed, NOS AF11x transistors will suffer from the same tin whisker problems as the duff transistors being replaced - sooner or later they'll die. Replacement with a more reliable transistor is always a better bet unless complete originality is essential.

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Old 8th Jul 2007, 10:03 pm   #9
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Default Re: AF117 replacements

Simon mentioned the AF239 specifically; I have an R200 here that is so equipped and would have to say, it works perfectly in this state. There is no difference that my ears or my various gadgets are able to detect between this set and others here with AF117s or 127s, or those with the BF450s.

That said, AF239s I have here are showing hfe of an average 25-30 so perhaps, Mersey Swimmer, yours were a duff batch or they changed the spec when another device was made obsolete? I don't know, maybe my tester has a fault, but this radio with three of these fitted does work and that's all the convincing I need.

Not up to the task of replacing an AF114 or similar in an FM i/f position for sure, but that would be when I'd crack out the AF124/5s.
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Old 8th Jul 2007, 10:08 pm   #10
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Default Re: AF117 replacements

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Originally Posted by Mersey_Swimmer View Post

Best stick to AF12x, particularly if repairing a Mullard module.

Pete

Yes, they're far too much trouble to chance having them perform badly after removal and replacement, even the relatively easy ones such as R500, RT8 etc.
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Old 8th Jul 2007, 10:59 pm   #11
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Default Re: AF117 replacements

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That said, AF239s I have here are showing hfe of an average 25-30 so perhaps, Mersey Swimmer, yours were a duff batch or they changed the spec when another device was made obsolete?
I'm going on the data in my venerable Towers book which gives a min hfe of 10. Problem is, I'm doing customer repairs on a (hopefully) commercial basis so I can't afford the time to experiment. Nor can I risk substandard performance. That time I actually tried an AF239S in a customer's set - no go. And I did try several specimens. After fitting an AF127 the job was a good'n. All the AF239S I have are lowish gain: hfe between 10 and 25. Well below what is expected from an AF11x or 12x.

I may try using AF239S in some of my own sets - I'd like to be able to use them for repairs as they are very cheap and easy to obtain.

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Old 9th Jul 2007, 7:29 am   #12
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Default Re: AF117 replacements

As far as originality goes, if you really sad, you could unsolder the cans on the AF11x, take pictures of the whiskers, and pot the AF12x in them.

I wouldn't dream of doing anything like that ....
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Old 9th Jul 2007, 2:31 pm   #13
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Default Re: AF117 replacements

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Sycom in Leatherhead still stock Mullard AF116s for 50p each but expect 50% of any NOS AF11* to be duds.
I find that duds can be easily repaired by twisting the C,B and E leads together and then connecting a PP3 battery between these and the screen lead for a second or two.This melts the offending crystals.
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Old 9th Jul 2007, 4:10 pm   #14
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Default Re: AF117 replacements

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Originally Posted by jim_jobe View Post
I find that duds can be easily repaired by twisting the C,B and E leads together and then connecting a PP3 battery between these and the screen lead for a second or two.
Yes this method often gets the transistor working again, but for how long? The whisker growth problem is a continuous on-going process in all AF11x transistors. So there is no guarantee that a 'repaired' or NOS transistor will continue to work for any length of time.

For a reliable repair the only sure course of action is to replace with a type of transistor than is not susceptible to the whisker problem. Such as the previously mentioned AF12x series, AF239, etc. Unless of course your main concern is to keep the circuit as original as possible
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Old 9th Jul 2007, 4:18 pm   #15
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Default Re: AF117 replacements

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Yes this method often gets the transistor working again, but for how long? The whisker growth problem is a continuous on-going process in all AF11x transistors. So there is no guarantee that a 'repaired' or NOS transistor will continue to work for any length of time.
I agree, I wouldn't use AF11x transistors in a permanent repair.

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Old 14th Jul 2007, 11:50 pm   #16
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Default Re: AF117 replacements

It will blow away the whiskers that have already caused short circuits, but it won't do anything for those that are still growing. Sooner or later another short circuit will develop.

I have used this method for some sets in my collection though, where the transistors could be removed and zapped again at a later date if necessary. So far, none have required a second zapping, but it's only a matter of time and luck.

Inside a module that is awkward to extract and disassemble, or in a set with a delicate PCB or other access problems though, I would go for a more reliable replacement. If I was repairing a set for someone else I wouldn't leave zapped AF11x transistors in it unless the owner knew and understood the situation.
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Old 19th Jul 2007, 7:32 pm   #17
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Default Re: AF117 replacements

Thanks everyone for the replies, I think it best to stick to the AF124-127 range, especially for those horrible Mullard modules.
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Old 19th Jul 2007, 9:03 pm   #18
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Default Re: AF117 replacements

As it happens, I've just been experimenting with replacement transistors for my tatty old TR82C.

The primary fault in this set was a corroded lead on the OC71 first AF amp. It was difficult to find a PNP transistor that wouldn't work in this position - all the germanium ones worked (OC45, old switching transistors, everything) and most of the general purpose silicon ones did too (BC214, BC327 and BC558 were all fine, and I've got hundreds of those).

While I was at it I tried subbing the final AF117 IF amp. Again a surprising range of transistors worked without problems, including an OC45 and a BC214, though the BC327 was less happy. An AF102 was also fine but I think those share the same construction as AF117s. All this was obviously without realignment or other component changes.

I haven't tried subbing the rather more demanding mixer/osc yet but the moral of this tale is to try whatever plausible transistors you have to hand - there's a good chance they'll be fine.

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Old 19th Jul 2007, 9:22 pm   #19
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Default Re: AF117 replacements

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I haven't tried subbing the rather more demanding mixer/osc yet...l
A while back I bought a tatty TR82D from off eBay for just 99p + P&P with the intention of breaking for spares. However it wasn't half as bad in the flesh as it looked in the photo's and I ending up restoring it instead.

To get it working again I had to replace all the AF117's in it with AF239's, and its continued to work fine ever since. No re-alignment necessary, which was a surprise!

Since then I've put AF239's in the mix/osc position in three other TR82's as replacements for AF117's and they've all been fine.

So when talking about TR82 sets the circuit used seems very tolerant of different transistors types. Can't guarantee other transistor sets of the period using AF117's would be as forgiving though.
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