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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 18th Oct 2020, 4:44 pm   #1
jubilado
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Question 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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Old 18th Oct 2020, 4:57 pm   #2
paulsherwin
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Default 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.
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Old 18th Oct 2020, 7:30 pm   #3
jubilado
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Default 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
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Old 18th Oct 2020, 7:32 pm   #4
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Default Re: AF117 Replacements - yet again

AF127 is my choice.
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Old 18th Oct 2020, 8:38 pm   #5
mervyn
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Default Re: AF117 Replacements - yet again

Quote:
Originally Posted by jubilado View Post
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
Never had a problem.. yes they are reliable and genuine

regards
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Old 18th Oct 2020, 8:46 pm   #6
Davewantsone
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Default 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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Old 20th Oct 2020, 1:21 am   #7
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Default 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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Old 20th Oct 2020, 8:20 am   #8
HamishBoxer
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Default Re: AF117 Replacements - yet again

I also have had stuff from Russia and no problems.
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Old 20th Oct 2020, 6:48 pm   #9
Electronpusher0
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Default 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.
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Old 21st Oct 2020, 1:26 pm   #10
jubilado
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Default 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
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Old 21st Oct 2020, 1:43 pm   #11
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Default 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.
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Old 21st Oct 2020, 2:02 pm   #12
Restoration73
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Default 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.
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