Bush TR114 Major Struggles

[Nowhere-Man]

The yellow cans will be OC81D and two OC81 transistors with sleeves over them like the red ones on the AF117s.
What is the component that is slightly obscured by the aerial between the coil connections? If this is a capacitor replace it before you do any other work as it is likely to be the power decoupling capacitor for the audio driver (OC81D) and will be causing the oscillation and overheating.

The method I use to deal with AF117s is to disconnect the screen lead by heating the solder and lifting the wire and cleaning the solder off the board so that there is no connection and then measure it again. Your meter will be reading the biasing resistors if the screen is connected to the earth track.
If there is now a reading when the isolated screen is measured it can be treated using a 12 volt power supply and a 100 ohm resistor and three silicone rectifier diodes.
First connect the diodes in series and connect the banded ends the same way round with the end one connected to the negative of the power supply and the resistor to the other end and connect it to the positive side of the power supply. You can if you want monitor the junction between the diodes and the resistor with a moving coil meter.
Now connect the junction between the diodes and the resistor to the screen and touch the negative of the meter and the banded end of the diodes to the electrode with the lowest reading when you tested with the meter. If you have the moving coil meter connected you should see a very short dip in the reading from a little under 2 volts for a fraction of a second. You should now find that the fault is gone.
In the data sheet for the AF117 the maximum applied voltage between any two pins is about 3 volts or so so the silicone diode shunt regulator is enough for you not to need to take the transistor out of the board.

O.K., I took your advice and removed the collector and screen pins from the PCB. I tested between the two leads and got an infinity reading whereas before I was getting an Ohms reading. So, your advice was spot on. I didn't test the other transistors so far. Thanks for that tip.

The capacitor by the ferrite coil I was asked about is a 6 volt cap but I'm not sure I could get it out without removing the dreaded string winding mechanism on the tuner to get access. I live in hope I don't have to later on face the prolonged task of another fiddly stringing.

Here is some very good news: I now have a very healthy audio output stage. There is a healthy hiss and a slight change on hiss when the waveband frequency change knob is used. Above all, on inserting a screwdriver on the end of the central volume pot terminal there is a very definite hum. Also, the same switch last night was doing nothing but now it works and you can switch the radio off with it.

I'll explain:

I realised today that what was really adding to a lot of confusion was the earphone jack plug. I'd been extra careful to get the pot terminals correctly wired but many wires run to and from the earphone jack and I think possibly a wire must have worked loose when I was soldering. I was starting to have major doubts about the wiring in that area so I decided to do away with the jack totally for now and simplify the whole thing. I then just wired from the transformer as you would normally do on a valve radio. I did actually take pics of the ear-jack at the beginning but found it was a bit jumbled. So, now I appear to have a healthy and hopefully undamaged audio output stage.

The problem now remains is how to inject the demodulated I.F. into my audio. Well, it could be a transistor but there are two important points I need to clarify: First of all, the central lug on the volume pot isn't connected to anything at this point. This is hard to explain but it did lead to the ear-jack. There is one snapped grey wire soldered on the PCB right at the edge (it had just snapped while I was soldering but I didn't notice at the time). Also a lower speaker wire had snapped off the PCB as well, near to the waveband change knob. So, there are 3 disconnected wires and it may well be the case one of these could get my reception back.

Lesson learned? Wires have a habit of snapping off while you're busy working.

[Nowhere-Man]

Ah! The dreaded 'Tin Whisker' problem with AF117s and their ilk.  BTW  I always replace AF11x transistors, rather than fiddle about trying to cure them.  Recently I have found, courtesy of a fellow meber of UKVRRR, that theree is a russian transistor, type no GT322, which can replace AF12x & AF11x types.  It is a TO-72, presumably alloy-diffused, device like the AF126/127, etc,  however it's base & emitter connections are reversed compared to those of the AF12x series -i.e. the same as tose of an AF139, 239 etc.  Specification, however, is similar to that of an AF127.  The GT322 is available from several eBay sellers at around £1 each in quantities of 15, so is a more economical buy that AF127s.
As to the problem with the overheating, I can only second the suggestions that smoothing capacitors may be the culprit(s), or possibly faulty output transistors, though it's just possible that the fault may have been caused by soldering connections to the earphone jack with the radio switched on.  Incidentally, if i may mention it here, the service info. for the TR114 is available from 'Vintage radio Service Data' ( part of UKVRRR), but you have to register as a member before you can purchase this.

Sadly I stopped using E-Bay totally. They recently automated the whole system and I was finding you can't contact actual people if a problem arises. It got to the point I was wasting a lot of time chasing after customer service including by snail mail. I have bought stuff on E-Bay before such as driving belts and I didn't used to have problems. Pity really as it's a huge market but boils down to personal experience.

Yes, I think you are bang on - the overheating would have been a wiring fault around the ear socket. Perhaps I've been very lucky I didn't blow my audio stage. I wasn't aware the speaker had gotten so hot till I touched it and then realised. Actually I did test it for ohms last night and it's about 14 ohms so quite high. Then again the specific speaker was made with the higher ohms reading.

As to the point about AF117's, there are many ways to look at it. I think the main thing is to get it working again but, on the other hand, I like to think it's as close to the same radio as possible. I have quite a thing about sixties radios because I'm a big Beatles and Stones fan and I like to imagine someone was listening to Love Me Do on this set when it first came out. I have a 1965 Transwave and somehow I think of Rubber Soul.

I guess I like the technical learning process of this hobby but I'm very nostalgic.

[tiv48]

If I have any thing with multiple wires that I am working on I ALWAYS take a lot of photos to refer back to.
saves a lot of time later.
Rob T

[Old Sparky]

Nowhere-Man, if you would like a few GT322 Transistors, I've just obtained 15 of them, so could sell you 3 or 4 for £1.25 each, which should cover both the price I paid for them and the postage. Send me a PM if you're interested.

[Nowhere-Man]

Nowhere-Man, if you would like a few GT322 Transistors, I've just obtained 15 of them,  so could sell you 3 or 4 for £1.25 each, which should cover both the price I paid for them and the postage.  Send me a PM if you're interested.

Can you explain a bit more about the actual transistor? Also, I'm curious as to the colour codes as I took one out today - an OC type and like the AF117's it has blue, green and yellow terminal sleeving. I can only assume blue is collector, yellow is emitter and base green. Anyone know for sure?

I'm a touch baffled as this transistor has turned out to be perfectly O.K. when tested off the PCB. It had been testing a leak between PN junctions both ways but not when I removed it from the PCB. And yet I tested many transistors that were still in place on a set and always get a reading in only one direction.

I was convinced the transistor was bad and snipped it out, leaving some lead behind so  it would be easier to put in the new one correctly.

Later I found any leak was simply the PCB but can here be any connection between base/emitter/collector both ways due to the board??

[Nowhere-Man]

O.K. so, to be honest, I'm beginning to think the work I've done so far has been a bit of a shambles. What irks me is it could well be the case I somehow damaged components as I'd have thought a very hot speaker cone would indicate some kind of a short?

At this point I've been getting a steady hiss and a loud hum if a screwdriver is placed on a switch terminal.

Someone said touching the base terminals with a screwdriver is one way to test a stage and when I tried that I got nothing (no buzz).

One question I have on my mind is a pretty simple one so far as valves are concerned but confuses me a bit with transistor sets. On a valve set you normally have the output pentode anode wired to a primary transformer with H.T. also connected via the transformer. So, I'm assuming if I want to simplify matters, I only need to get battery 9 volt supply to the transistor radio transformer, one speaker connected also to the transformer and then the other side to ground. This is what I did and I have a steady hiss but no stations.

Any chance there was a voltage overload? The small transformer does seem to show traces of black at the top.

Most of you have suggested I change the main H.T. capacitors so it does seem now I'll have to go ahead with that. To do so I'll need to remove some parts top get access so will at some point have to restring the tuning mechanism.

[Old Sparky]

IIRC, there was no standard colour coding for transistor lead-out wires, and different manufacturers used different colour sleeves to denote collector, base & emitters. OC170, AF117, etc have their lead-outs in this form 'e,b,s, c' (i.e. the gap between the screen and collector is bigger than that between any of the other leads, whereas OC71, 81, etc., and some of the AC127 types have a coloured spot on the metal case to indicate which lead is the emitter. Data Books, such as those published for many years by Mullard and Towers are very helpful in identifying transistors, providing details of pin-outs, Hfe, Ic., and other parameters. Entering a type no. into a search engine will also produce on-line data sheets for many devices. (Apologies if I'm stating the obvious here!) As to misleading readings when checking transistors in situ, this is usually due to resistors or inductors being connected, not always in an obvious way, in parallel to semisonductor junctions. It's easy to assume that a transistor or other device is faulty,, when the problem is in the associated circuit. I've done so myself, including a couple of times recently, and I've been working with electronics for about 44 years!

[Mark Hennessy]

A few months back I discovered that Towers is available on-line: https://archive.org/details/TowersIntern...orSelector

It's a bit intimidating at first glance, given that it is almost nothing but numbers, but that's only because there are so many transistor types in existence. What is really useful, though, is the appendices in the back that show you the physical layout and pin-out of the various transistors...

Speaking very generally, do bear in mind that germanium transistors can give strange readings, even when removed from the circuit. But the junctions are very reliable, notwithstanding the problems with tin whiskers. After tin whiskers, most faults are caused by capacitors.

Some more about vintage transistors here: http://www.markhennessy.co.uk/articles/v...istors.htm

There is a mine of information about repairing all types of vintage radios here: http://www.vintage-radio.com/repair-rest...index.html

Cheers,

Mark

[Nowhere-Man]

Funnily enough, I've been a bit discouraged of late. I started out with 3 or 4 successful repairs (fairly easy ones) but now it's a bit like being in the deep end and a poor swimmer.

Does anyone ever get mental blocks or ever had a mental block? When it happens it's like all your knowledge of electronics goes out the window and you just get totally puzzled. I get like this sometimes and then, after a break, I try and think it over more rationally and then wonder why I had gotten so confused.

Anyway, now to update you all:

I decided to take the advice about changing the capacitors as it can't do any harm to roll my sleeves up and give it my best shot. Today I removed the stringing mechanism and made detailed diagrams. I also made a very detailed diagram of the ferrite rod connections and then snipped the wires. I left some wires partly on the rod just in case I get a mental block and then the colours will make it much easier. If I had 2 blue wires, I also marked one of them in biro if it needed to be fixed on a different lug. And I took pics.

Now, here is where I need advice: I removed the first main capacitor which I believe is a 6 volt 50 Mf (the one that was spotted by the ferrite rod) This turned out to be a hell of a job as I was at a loss as to how to match the component lead with the corresponding solder joint the other side. I had to try and count the holes and then use the meter till I got a safe zero (although other points could also give a zero). Anyway I got out the trickiest one out today but there is some lead left in the PCB pinhole.

Would it be possible to drill out these pin holes with a very fine drill from the component side and through to the solder side? I was thinking of a very fine but strong drill and straight through so I can then easily fit the new capacitor.

Lastly the transistors. I find those OC yellow sleeved transistors are bullet proof. They're not worth chucking away. I managed to repair it by  making a tiny round hook on a fine wire and soldering it to the transistor. It seems robust and the P/N junctions still test fine.

[Nowhere-Man]

IIRC, there was no standard colour coding for transistor lead-out wires, and different manufacturers used different colour sleeves to denote collector, base & emitters.  OC170, AF117, etc have their lead-outs in this form 'e,b,s,  c' (i.e. the gap between the screen and collector is bigger than that between any of the other leads, whereas OC71, 81, etc., and some of the AC127 types have a coloured spot on the metal case to indicate which lead is the emitter.  Data Books, such as those published for many years by Mullard and Towers are very helpful in identifying transistors, providing details of pin-outs, Hfe, Ic., and other parameters.  Entering a type no. into a search engine will also produce on-line data sheets for many devices.  (Apologies if I'm stating the obvious here!)  As to misleading readings when checking transistors in situ, this is usually due to resistors or inductors being connected, not always in an obvious way, in parallel to semisonductor junctions.  It's easy to assume that a transistor or other device is faulty,, when the problem is in the associated circuit.  I've done so myself, including a couple of times recently, and I've been working with electronics for about 44 years!

From a superficial glance, it seems most very early transistors were bunged in with the base pretty much bang in the middle. I assume that is mostly the case. I have a 1959 Bush and I always tend to get one way readings between green centre wire and the two external leads. So, I assume the middle one is the base.

Anyway, I'm now just going to try my best, change the capacitors, check the waveband and ferrite rod and see if it can be done.

Any tips welcome.