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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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7th Jul 2007, 9:37 pm | #1 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
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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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Simon BVWS member |
7th Jul 2007, 10:37 pm | #2 |
Pentode
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Location: London, UK.
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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.
HG MICKE |
8th Jul 2007, 12:53 am | #3 |
Moderator
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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. Paul |
8th Jul 2007, 1:58 am | #4 |
Heptode
Join Date: Aug 2006
Location: Sheffield, South Yorkshire, UK
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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 |
8th Jul 2007, 12:34 pm | #5 | |
Retired Dormant Member
Join Date: May 2007
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Re: AF117 replacements
Quote:
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. Pete |
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8th Jul 2007, 1:03 pm | #6 |
Heptode
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Location: Ripon, N.Yorkshire, UK.
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Re: AF117 replacements
If you want AF11X series, I think Birkett in Lincoln still has some at about 75p.
Jim |
8th Jul 2007, 6:37 pm | #7 | |
Nonode
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Re: AF117 replacements
Quote:
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. Howard |
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8th Jul 2007, 8:21 pm | #8 | |
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Re: AF117 replacements
Quote:
Paul |
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8th Jul 2007, 10:03 pm | #9 |
Heptode
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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. [img]http://farm2.static.***********/1192/756662968_3211f5cb8c.jpg[/img]
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John. |
8th Jul 2007, 10:08 pm | #10 | |
Heptode
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Re: AF117 replacements
Quote:
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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John. |
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8th Jul 2007, 10:59 pm | #11 | |
Retired Dormant Member
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Re: AF117 replacements
Quote:
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. Pete |
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9th Jul 2007, 7:29 am | #12 |
Dekatron
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Location: Near Leeds, West Yorkshire, UK
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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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Mike. |
9th Jul 2007, 2:31 pm | #13 | |
Heptode
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Re: AF117 replacements
Quote:
Jim |
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9th Jul 2007, 4:10 pm | #14 | |
Heptode
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Location: Sheffield, South Yorkshire, UK
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Re: AF117 replacements
Quote:
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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9th Jul 2007, 4:18 pm | #15 | |
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Re: AF117 replacements
Quote:
Paul |
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14th Jul 2007, 11:50 pm | #16 |
Administrator
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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. |
19th Jul 2007, 7:32 pm | #17 |
Nonode
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Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
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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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Simon BVWS member |
19th Jul 2007, 9:03 pm | #18 |
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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. Paul |
19th Jul 2007, 9:22 pm | #19 | |
Heptode
Join Date: Aug 2006
Location: Sheffield, South Yorkshire, UK
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Re: AF117 replacements
Quote:
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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