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-   -   AF 11* Transistors. Innards Removal? (https://www.vintage-radio.net/forum/showthread.php?t=143839)

tim.norris 10th Feb 2018 3:50 pm

AF 11* Transistors. Innards Removal?
 
Is there an easy way of removing the innards from a AF117? I have a couple of radios I want to preserve the look of by stuffing with the later 127 etc. Plus I could lengthen the leads at the same time as the 126 etc ones seem woefully short.

Regards, Tim.

ukcol 10th Feb 2018 4:43 pm

Re: AF 11* Innards Removal ?
 
I assume you could most easily open an AF117 up with a pipe cutter.

If you are going to the trouble of opening one up why not clean out the gunk and the tin whiskers? Then you could refill the case with something that the tin whiskers could not penetrate. Silicon sealer may be suitable, reassembling the transistor before the sealer goes off?

I don't know what chemicals are in the filler in these transistors, so be careful as it may be toxic.

Paul_RK 10th Feb 2018 4:56 pm

Re: AF 11* Transistors. Innards Removal?
 
Experimenting with a method I found proposed (here?) some years back, of eliminating tin whiskers by applying a soldering iron to the AF117 can sufficiently to melt them, I found the can popped off the contents quite readily. Whether the approach succeeded for me in reclaiming any transistors I can't recall, but it certainly seems a promising way of emptying the can if that's all you want to do: or a less drastic heat source (hot water bath?) might perhaps serve as well.

Paul

vinrads 10th Feb 2018 4:58 pm

Re: AF 11* Transistors. Innards Removal?
 
Regarding disguising the AF127. Sorry is it just me but ???

dseymo1 10th Feb 2018 5:22 pm

Re: AF 11* Transistors. Innards Removal?
 
I think the filling is silicone grease.
However, my impression is that exposing the guts to normal, 'dirty' atmosphere will make them unreliable - isn't that why they're hermetically sealed?
As far as disguising transistors is concerned, bear in mind that many types were offered in cosmetically different versions anyway, at different times and by different manufacturers, so there's no really 'standard' appearance.

tim.norris 10th Feb 2018 5:26 pm

Re: AF 11* Transistors. Innards Removal?
 
Vinrads, I know it's a lot over the top but it's a rare Bush ETR 92 that I just want to look as original as possible, all the run of the mill stuff just get AF12* straight swops!

Paul, will give the heat method a try.

Regards, Tim.

poppydog 10th Feb 2018 5:41 pm

Re: AF 11* Transistors. Innards Removal?
 
I drilled mine out in a pillar drill and stuck the empty AF117 can over the top of some GT322bs in my R300.

Poppydog

Nuvistor 10th Feb 2018 5:52 pm

Re: AF 11* Transistors. Innards Removal?
 
This is how NASA opened one up, an interesting read as well.
https://www.vintage-radio.info/download.php?id=371

factory 10th Feb 2018 8:28 pm

Re: AF 11* Innards Removal ?
 
Quote:

Originally Posted by ukcol (Post 1015839)
If you are going to the trouble of opening one up why not clean out the gunk and the tin whiskers? Then you could refill the case with something that the tin whiskers could not penetrate. Silicone sealer may be suitable, reassembling the transistor before the sealer goes off?

Be careful with using silicone sealants, those that are acetic acid based will cause corrosion and probably ruin them. Look for non-corrosive types intended for use with electronics if you are going to try this.

David

MrBungle 10th Feb 2018 8:34 pm

Re: AF 11* Transistors. Innards Removal?
 
Vaguely on topic but when I was a kid my pyromaniac cousin found they blow the glass seal out (loudly) if you chuck them in a fire. Taking it slightly less extreme perhaps application of heat may work. Then you could reseal the new transistor in with epoxy.

Herald1360 10th Feb 2018 8:42 pm

Re: AF 11* Transistors. Innards Removal?
 
If it's all cleaned up and working, silicone grease as per original will give you another 30 years or so......

Or there are the (somewhat) expensive non silicone grease filled OC169's talked about elsewhere in the forum which are whisker free drop in replacements.

Beardyman 10th Feb 2018 9:47 pm

Re: AF 11* Transistors. Innards Removal?
 
Please bear in mind these devices have some very toxic substances within them. Arsenic, Beryllium, Phosphorus & several other very nasty substances, please be very careful! I know the concentrations are very low but if by some quirk of fate or circumstance they happen to be ingested or make their way into your eyes for instance then the consequences are unthinkable. Please do be careful.

Refugee 11th Feb 2018 2:35 am

Re: AF 11* Transistors. Innards Removal?
 
They are pretty safe.
It is the RF output transistors in old industrial walkie-talkies that have nasty stuff in them.

Boater Sam 11th Feb 2018 3:52 am

Re: AF 11* Transistors. Innards Removal?
 
A hot iron will pop the can off and then you can put a new transistor inside. Do not use silicone sealer, it rots most metals. I use Blue-tack or the white equivalent.

Argus25 11th Feb 2018 11:46 am

Re: AF 11* Transistors. Innards Removal?
 
5 Attachment(s)
Tim,

You really do not have to attempt such a plan to remove or replace the innards of the AF11x transistor. I will explain why (multiple reasons) and I have attached 5 images.

Firstly, it is quite easy to repair the AF11x transistor and remove all the tin whiskers and grease. It is an old technique now (at least in the Southern hemisphere), my brother perfected it in NZ in the late 1980's when these transistors started to fail, long before the phenomenon of tin whiskers was widely known and before NASA wrote their paper.

There are two methods, I would recommend the latter as it is a heat free method:

Two 1.5mm dia holes are drilled in the side of the case. They are marked with a caliper and scribe to initially start the surface cut with a 1mm drill. The ideal place to drill these is 2mm from the top surface edge and 3.5mm from the bottom surface edge, on opposite sides and on an axis that is at a 45 degree angle with the axis of the transistor's lead array.

Then a plastic jet tube on a can of CO contact cleaner or trichloroethylene like spray, is cut down to a taper with a scalpel and pushed into one hole, the high velocity jet pushes all the grease and tin whisker fragments out the other hole. Spray into both holes for a while to ensure the entire internal case is cleaned out. As the photo shows the holes are then covered in solder, to seal the case much like a quartz crystal case is sealed.

Under high magnification, the washings from the above process contain tin whisker fragments and the original grease. Luckily, since the thermal dissipation in these transistor junctions is so low, it is not in fact necessary to replace the grease.

(by the way, sealing the transistor with air in it results in no long term damage to the transistor crystal. In fact many IC's and transistors were once left bare, in air, provided they were in a sealed enclosure. Early Hugh's Corporation Calculator watches were like this, I have one and the many hundreds of semiconductor junctions, much smaller in geometry than AF11x, are still fine after 40 or more years).

The only problem with the above method (which is why I have added the other photos) is that the transistor case gets heated with the soldering iron. This is why it is also a bad idea to pop off the top, too much heat is needed and often the top is stuck firmly on too and won't come off even with the tin/solder melted. The germanium transistor crystal is easily damaged by heat, I found this by subjecting transistors to pre & post repair testing in a careful lab setup/test jig.

So over the years I developed a "heat free" version of the above repair. This involved drilling smaller holes. I found that two at the top sufficed, with 1mm metric threads. Then rather than heating the case I was able to fit 1mm metric screws to seal it that way. It required a 0.7mm outer diameter hypodermic needle to do the washout and by transferring the cleaning agent into a syringe. A small amount of silver Humbrol paint can be used over the screw head to make it less obvious. See photos. The ideal screw length is 1mm but if both holes are near the top a longer screw is permissible. 1mm taps & small head screws are easy to get in Japan etc, you might have to hunt around on the net.

However, I reserve this repair process now for one transistor, and one alone, the AF118 (as it has very few equivalents being a high voltage video output transistor).These do require a grease re-fil. So I have bought all of my AF118 stocks of this part back from the tin whisker death zone.

Unless you are hyper enthusiastic to repair your AF114-7 types I would simply replace them with the AF178. These are an excellent transistor, not a small and difficult to fit type like the AF127, and they look really good in vintage radios and have equal or better specs. If you like you can easily extend their leads. The 2N2084 is also an excellent long leaded option. But I agree with you, AF125 etc just doesn't look right and are a difficult fit.

Hugo.

ukcol 11th Feb 2018 12:20 pm

Re: AF 11* Transistors. Innards Removal?
 
Thank you very much Hugo, that is extremely useful information.

Moderators,

Can I suggest that post number 15 above be copied to a new locked thread in the components and circuits section and made a sticky.

AC/HL 11th Feb 2018 2:04 pm

Re: AF 11* Transistors. Innards Removal?
 
There are quite a few threads about various aspects of this phenomenon. All are in this section, so not too difficult to find.

Philips210 11th Feb 2018 2:04 pm

Re: AF 11* Transistors. Innards Removal?
 
Thanks for posting this excellent write up Hugo. I'm fascinated by this. This technique could be applied to NOS transistors with no apparent problem as a preventative measure. I have come across the tin whisker problem on other Mullard germanium transistors, most recently a AC188 in a Roberts R707. I suppose a similar method could also be applied to this type of transistor.

I would like to try out your method and it would be interesting to see the contents under a microscope.
I wonder if the whisker growth problem is only confined to tin and it's alloys or are there any other metals which exhibit the same issue?

Regards
Symon

60 oldjohn 11th Feb 2018 3:15 pm

Re: AF 11* Transistors. Innards Removal?
 
Quote:

Originally Posted by ukcol (Post 1016072)
Can I suggest that post number 15 above be copied to a new locked thread in the components and circuits section and made a sticky.

Hugo that is very interesting, and I would second the above comment. While the sticky briefly covers "Cleaning out the can) #15 covers this but goes in much further detail, re not refilling ect.

John.

AC/HL 11th Feb 2018 3:38 pm

Re: AF 11* Transistors. Innards Removal?
 
I've added a link to post 15 to that thread.


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