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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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18th Oct 2020, 4:44 pm | #1 |
Triode
Join Date: Jun 2019
Location: Edinburgh, Scotland, UK.
Posts: 30
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AF117 Replacements - yet again
Hi, I know I am a bit late to the party but the threads/posts I can find regarding AF117 all seem to be a few years old. As I have just started the process of "restoring" some of the old radios I have accumulated I wondered if there was a current preferred/available replacement for those old AF117s?
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18th Oct 2020, 4:57 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,783
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Re: AF117 Replacements - yet again
They really aren't critical. Your options are:
Zap the tin whiskers and refit the original transistors Fit other Ge types with an adequate transition frequency Fit Si PNP types (sometimes requires bias changes for optimum performance) There are threads covering all three approaches if you search the forum. If you have some potentially suitable replacements to hand, try them before buying anything. |
18th Oct 2020, 7:30 pm | #3 |
Triode
Join Date: Jun 2019
Location: Edinburgh, Scotland, UK.
Posts: 30
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Re: AF117 Replacements - yet again
Thanks for the reply.
Since I am just starting out on this I do not have the technical knowledge about transition frequency or bias changing. As for replacements, I have looked at the GT322B as mentioned by others as a substitute but they all seem to be supplied from Russia, Bulgaria or Ukraine. Has anyone tried these sources and are they genuine and/or reliable? As a result it may be that I am heading down the road of zapping. Neil |
18th Oct 2020, 7:32 pm | #4 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,192
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Re: AF117 Replacements - yet again
AF127 is my choice.
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18th Oct 2020, 8:38 pm | #5 | |
Hexode
Join Date: Mar 2005
Location: Whitfield, Dover, Kent, UK.
Posts: 258
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Re: AF117 Replacements - yet again
Quote:
regards Merv |
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18th Oct 2020, 8:46 pm | #6 |
Hexode
Join Date: Dec 2011
Location: Wigan, Greater Manchester, UK.
Posts: 291
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Re: AF117 Replacements - yet again
Before unsoldering the AFXXX transistors from a radio cut the screen wire off. The whiskers usually short to the can (screen lead) which is earthed and stops the transistor from working. If you do need a replacement I have on quite a few radios fitted a PNP silicon BC557 without any modification to biasing. To maintain original look of set I dig out the insides of the faulty AFxxx and stick it over the BC557.
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20th Oct 2020, 1:21 am | #7 |
Hexode
Join Date: Mar 2018
Location: Bishop Auckland, County Durham, UK.
Posts: 373
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Re: AF117 Replacements - yet again
The Russian transistors are fine. There has been a hike in the price of some Germanium transistors over the past few years. I understand they are popular with people who construct guitar "fuzz boxes". Many radios such as Hacker Sovereigns have a positive earth and leakage between collector and can will shunt the IF transformer primary winding. This can cause unusual faults like distorted sound on AM and lack of sensitivity. People have their own ways of dealing with the AF117 transistor problem and there are many posts about this on the forum.
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20th Oct 2020, 8:20 am | #8 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,923
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Re: AF117 Replacements - yet again
I also have had stuff from Russia and no problems.
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20th Oct 2020, 6:48 pm | #9 |
Nonode
Join Date: Jun 2016
Location: Bognor Regis, West Sussex, UK.
Posts: 2,287
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Re: AF117 Replacements - yet again
I repaired a Roberts R500 today, it was intermittent, tapping the board would cause the signal to come and go, classic tin whiskers.
I took Paul at his word (that most PNP silicon transistors would work in the IF stages) and fitted 2N3906s and it worked fine, better in fact. I did not try using them for the oscillator, I used one of my stock of AF127s. The set now works fine, no sensitivity to tapping anywhere. |
21st Oct 2020, 1:26 pm | #10 |
Triode
Join Date: Jun 2019
Location: Edinburgh, Scotland, UK.
Posts: 30
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Re: AF117 Replacements - yet again
Thanks for all the replies. I have 20 or so radios from a variety of different manufacturers so will try a variety of these methods on different ones to see how I get on. Most of these are here to stay so with those I can try snip/zap then replace if needed with whatever in the future. I am reluctant to replace too many with AF127s given the price that these seem to go for these days.
Thanks again Neil |
21st Oct 2020, 1:43 pm | #11 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,783
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Re: AF117 Replacements - yet again
Whatever else you do, it's worth buying 50 or 100 2N3904s and 2N3906s. They only cost a pound or two from Chinese eBay sellers and come in useful for all sorts of things.
I agree that AF12x types are quite expensive nowadays, and while they are the ideal AF11x replacement, other cheaper types will work perfectly well. If you keep a range of types to hand you can experiment to find the most effective substitution at the lowest cost. |
21st Oct 2020, 2:02 pm | #12 |
Nonode
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
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Re: AF117 Replacements - yet again
I have kept an old set and fitted a socket where the AF117 was, enabling dynamic test
which other test gear does not provide. You may also get lucky. I was given some surplus devices but only one was marked; SFT316 - made by Mistral (Italy) - and these work very well. I remember these were used in many of the Amtron construction kits. |
19th Dec 2020, 6:47 pm | #13 | |
Heptode
Join Date: Jan 2018
Location: Folkestone, Kent, UK.
Posts: 709
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Re: AF117 Replacements - yet again
Quote:
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19th Dec 2020, 6:49 pm | #14 |
Heptode
Join Date: Jan 2018
Location: Folkestone, Kent, UK.
Posts: 709
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Re: AF117 Replacements - yet again
i will look at getting some 2n3906s ,many thanks all for the very useful info
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19th Dec 2020, 8:33 pm | #15 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,798
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Re: AF117 Replacements - yet again
Keeping 2N3906 and 2N3904 in stock is a good move. It's mazing what they can replace.
David
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