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Old 26th Jul 2018, 11:29 pm   #21
mhennessy
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Default Re: Hacker Sovereign 11

It sounds like you definitely have an amplifier fault. Though I'm intrigued by the comment about the Fane speaker being much better than the Celestion. Having measured lots of Hacker sets and highlighted the differences between various speaker models (details somewhere on this forum), I would expect it to be slightly different - perhaps a little better as a matter of personal preference - but from your description it's possible the Celestion speaker is not in A1 condition. Which is not unusual... Still, it's all a bit subjective.

Either way, yes, start with the amp - everything you need to know about that has already been said, but shout if further explanations or guidance is required
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Old 27th Jul 2018, 1:20 am   #22
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Default Re: Hacker Sovereign 11

Ignore the remark in my post #19 about the voltages across the emitter resistors, there is no point in comparing the voltages across the two output transistor emitter resistors in the Hacker circuit, because they are effectively in series, so the voltage drop across them will be equal (and indicate the current you measure in the test link as well), regardless if one transistor if unwell. (that test or comparison only works in output stages with transformers where the emitter resistors are returned to the supply ground).

Looking at the Hacker circuit though, which I now have in front of me, due to the fact that all the stages are direct coupled; one of the most important & simple tests is the voltage between the output transistor emitters at the junction of the two 2.2 Ohm emitter resistors, it should be very close to half the total power supply voltage (the voltage you would measure between the two output transistor collectors) if all is well with every transistor stage.

This "half rail" voltage comes about due to the fact that the input transistor T1 (a bc108 on my circuit) is biased so that its collector voltage controls the base voltage of T2 (the fine adjustment for this is the 50k pot RV3).

A voltage from T1's collector, is coupled directly to the base of T2 another BC108. T2 also receives, at its emitter, a sample of the output voltage via the 1.8k feedback resistor from the output at the junction of the two 2.2 Ohm emitter resistors.

Therefore, T2's base emitter junction threshold voltage (about 0.6V) acts like a comparator in a negative feedback loop to stabilize the DC output voltage at the junction of the two 2.2 Ohm resistors, to close to half the supply rail voltage. For example as the output voltage rises, so does T2's emitter voltage, turning T2 off, T2's collector voltage rises, this starts to turn off T4, T4's collector voltage drops and so does the output voltage at the junction of the two 2.2 Ohm resistors. So it self stabilizes.


From that you can see that if all is well with every transistor's DC bias conditions at least and all the resistors are ok and there is no capacitor leakage anywhere, then with the 50k adjustment somewhere near the center of its range the output voltage at the junction of the two 2.2 Ohm resistors should be 1/2 the supply rail.

One way in this sort of circuit to check if the complimentary output transistors are likely similar and both ok, is to compare their base to emitter voltages, they should be fairly close and of course opposite polarity. The base of the npn (AC176) being more positive than its emitter perhaps be a few hundred mV and the base of the PNP(AC128) being more negative than its emitter.

hope that helps.

Last edited by Argus25; 27th Jul 2018 at 1:27 am.
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Old 27th Jul 2018, 9:13 am   #23
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Default Re: Hacker Sovereign 11

Think I'd just replace T1 (BC148 lockfit) with a standard BC108 to start with. This will more than likely cure the problem. If not, then resort to Argus25's more scientific approach, although I'm not sure this would identify a noisy transistor.

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Old 27th Jul 2018, 10:54 am   #24
mhennessy
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Default Re: Hacker Sovereign 11

It would be good to identify what the fault actually is. This is the trouble with subjectivity - I might be able distinguish between noise and distortion, but someone else might well hear noise and think of it as distortion. We're all different

To tell if it's noise or distortion, turn the volume to minimum and press your ear to the speaker. If you can still hear audio, use the ISM function to mute the audio by tuning to a dead part of the FM band. Having done that, can you still hear a noise? It's likely to be a low-frequency rumble rather than a hiss. If present, that rumble will certainly interfere with quiet music - which is why one might well describe it as distortion.

Before changing anything, check the settings of the two presets. It's very simple to do - I gave the values you need in post #15. As part of this, it's worth giving the pre-sets a small shot of switch cleaner and exercising them. This is just something that should be done to any set as it arrives - knowing that the mid-point and quiescent current is correct tells you an awful lot about the health of the amplifier. Note that this was rightly suggested as early as post #2.

If the quiescent current and mid-point voltage settings are correct and the "distortion" persists, then change T1. That cures most cases of noise, but sometimes you have to consider changing T2 (although as I mentioned before, I change both on aesthetic grounds). Very occasionally, resistors can play up, but again, as mentioned before, resistor problems are relatively rare of the A205 amplifier, but much more common on the A209 used in the RP38A.
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Old 27th Jul 2018, 4:24 pm   #25
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Default Re: Hacker Sovereign 11

The logic behind my suggestion (post #23) is that a noisy T1 is a stock fault in these sets and it's a five minute soldering job to swap it for a BC108. In fact, pretty much any old general purpose npn silicon transistor will work in this location and test the theory. The 'amateur hacker' approach I guess!

In any event, with all the good advice already put forward by others I'm sure the Hacker will be singing happily again very soon.

Alan
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Old 27th Jul 2018, 6:33 pm   #26
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Default Re: Hacker Sovereign 11

thank you guys for the invaluable advice .I will investigate further and let you know how i get on . Both these sets were bought new by my parents so i know their history and i would like to keep them both working for as long as i am around .Thanks again
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Old 27th Jul 2018, 8:31 pm   #27
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Default Re: Hacker Sovereign 11

Just spent the last half hour in the shed [more like a sauna at the moment] removing the amp. I have to say its a thing of beauty with everything clearly labelled looks just like the ones in my hacker gram only smaller. looking at it there's nothing obvious staring at me till i turn it over and see the corrosion on the strip next to the three transistors. Could this be a problem maybe. Will carry out some of your recommended tests over the weekend.
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Old 27th Jul 2018, 8:40 pm   #28
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Default Re: Hacker Sovereign 11

Hello,
Your problem may well be the transistor with the blue heat sink on it, I think it is T4. I t throws up loads of faults depending where itís leak is. I have had it produce windy hissy sound at low volume, no sound with the volume control turned higher and no way to set the mid point.
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Old 27th Jul 2018, 8:50 pm   #29
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Default Re: Hacker Sovereign 11

I don't think the corrosion is a problem.

Yes, T4 can cause a multitude of problems. It's an AC128 - perhaps less easy to source these days than replacements for T1 and T2. But a better description of the fault would help to narrow this down. When T4 plays up, it tends to make more conspicuous problems than (my understanding of) the fault, but anything is possible!
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Old 27th Jul 2018, 9:21 pm   #30
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Default Re: Hacker Sovereign 11

i really dont know how to describe the fault any better than i have .All i can say is when the amp from the Hunter is in use the fault is gone and the sound is significantly improved .At least we know the fault is with the Sovereigns amp or speaker .
before doing anything else and Just to completely eliminate the speaker i will remove it from the cabinet and connect it to a different source and see how performs
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Old 27th Jul 2018, 9:52 pm   #31
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Default Re: Hacker Sovereign 11

But what does it actually sound like?

Q. Is there a low frequency rumbling noise that is there all the time, even when there is no audio?

Q. Or is there a "roughness" to the sound? Almost like a scratching?

Q. Is is present at medium and high volume too?

Q. Does it change as you alter the treble and bass controls?

Answers to these sorts of questions help enormously. I know it might not be easy, but it's really worth taking the time to learn how to subjectively describe the symptoms, especially given that we are unable to hear what you do. In this thread you've probably had every possible fault condition possible (apart from the amp being completely dead), so at least every base has been covered, but a better description would have resulted in more targeted, concise advice.

Your description of what happened when you tried parts from the Hunter was very helpful, but none of that described what the faulty amplifier sounds like.

I hope that helps

Mark
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Old 27th Jul 2018, 10:14 pm   #32
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Default Re: Hacker Sovereign 11

ok Mark .tomorrow i will do everything you have suggested above .The first time i noticed this was one evening .I was listening to radio 4 [not music someone was talking] .At first i thought the speaker is rubbing somewhere .I didnt try MW or LW just FM .As i turned the volume down even further the rubbing sound or distortion got worse .We are now at the point where i have to have my ear up against the radio to hear anything.Getting back to when i used the Hunters amp the sound was much better .Lots more treble and crystal clear sound overall just a vast improvement.As i said earlier i will test the speaker again before i do anything else .I dont want to make things worse so i am treading carefully.
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Old 28th Jul 2018, 1:09 am   #33
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Default Re: Hacker Sovereign 11

One of the things that characterizes a good repair, from a poor one, it is a "targeted repair" based on measurements and deductions. The worst thing a technician can do is to start replacing parts with a "stab in the dark" approach. The reasons for this are multiple and more complex than you might first think:

1) More pcb damage is done. Remember in these old radios the adherence of the foil to the phenolic board is much more fragile and heat sensitive than a modern pcb and there are no plated through holes which give extra support to component pads. So care and temperature controlled de-soldering & soldering is required to preserve the pcb.

2) New faults can be introduced if there are issues with the substituted parts.

The above can lead to a cyclical degradation of the board being repaired.

3) But, here is the worst of it:

Human psychology explains that this blind approach to servicing electronic equipment is rewarded and sustained by the phenomenon of intermittent reinforcement. For example if this cut & try approach works only 1 in 7 times, that reinforces the technician's bad behavior and it is very difficult to extinguish it, even with a run of multiple losses or failures. (this is why rewards in gambling, for example the Pokies or scratch tickets, give a reward at a rate of about 1/7, so the gambling is reinforced) This was all worked out many years ago with an enclosure called a Skinner Box, with a rat being rewarded with a grain of rice for pushing on a metal bar and various reinforcement schedules were tried. If the rat is rewarded for pushing on the bar at a rate of about 1 in 7, and then if the reward is withdrawn, the rat keeps trying for the longest number of attempts before it gives up. Turns out it is about the same rate for humans.(I certainly don't mind being compared to a rat myself, they are spectacularly intelligent animals for their size and I'm very fond of them)

Therefore, the best move is to take multiple measurements on the faulty pcb before concluding & doing anything.

As noted in my previous post the minimum equipment is a multimeter +/- a crystal earphone.

So do what you are doing, take your time, think about it, read about these amplifier circuits, make measurements (especially the 1/2 rail voltage) and collect some data. Then with that data the forum members can also help guide you to the fault and it can be a "targeted repair".
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Old 28th Jul 2018, 5:13 am   #34
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Default Re: Hacker Sovereign 11

In the days when every town had several radio and TV repairers, repairs were being done in commercial quantities. The vast majority of repairs were of 'standard' faults, where there was prior knowledge of the weaknesses of each model, of the symptoms of the usual faults they suffered from, and of what to change to fix them. This knowledge was passed down from mentor to apprentice in workshops, and magazines like 'Television' and 'Radio Constructor' passed it around a wider distribution. Rather like "The Archers" has been used to pass information on changes in farming, Dick and Smithy did their bit for radio repair.

This approach to repair is fast and economical, provided the fault is a known one. It falls down when the model is an unusual one or the fault is unusual. Practitioners of this method made their livings from it, and they got some mileage out of cross-applying their knowledge when unfamiliar models showed up with familiar symptoms. They could go looking for comparable components to try swapping.

The other approach is to understand how radios etc, work at both system and circuit level and to deduce from the symptoms, to look at waveforms and voltage measurements and decide where the fault must lie. This method needs a lot more understanding, but maybe less total knowledge. From the point of view of a repair shop, it is glacially slow and therefore uneconomic in isolation, but this is how the knowledge of the standard faults originated. Someone had to be the first, or at least the first in each workshop.

A commercial repair workshop needs both methods on tap. One or two individuals who can work out solutions to off-piste faults, and then a larger number who can crank out the more common standard repairs.

As a schoolkid, I was told that the colour TV course at the local tech took six years to complete, presumably as a day-release sort of thing, while you could get a degree in three years. Six years sounded like three consecutive lifetimes at that age.

The knowledge of the standard faults lives on in this forum, and in the archived copies of trade magazines. If you need to fix a standard fault, it is very helpful.What you learn from "David thingumybob told me to replace Q123, I did and it burst into life" may not be much, but you now have a working radio.

The ability to understand signals and circuits and to work out faults and fixes as if they've never been seen before is more necessary nowadays where there aren'y loads of workshops doing repairs in industrial quantities. If you need to fix something, thoroughly understanding the thing, its fault and the solution gives abilities that apply to many things.It amounts to developing fault finding skills as an alternative to developing encyclopaedic knowledge of pre-solved faults. The two approaches aren't quite so separate, there is a lot of crossover.

By the way, the thread title is a bit misleading. It says Sovereign eleven, when it really means sovereign two (in roman numerals). It might be worth changing the 11 to II to make future searching easier.

David
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Old 28th Jul 2018, 6:11 am   #35
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Default Re: Hacker Sovereign 11

Quote:
Originally Posted by Radio Wrangler View Post
The ability to understand signals and circuits and to work out faults and fixes as if they've never been seen before is more necessary nowadays where there aren't loads of workshops doing repairs in industrial quantities.
David,

Yes this is my preferred method.

But having said that there are least two scenarios where it can fall down.

One is when there is poor or no documentation. Often a lot of modern equipment; there are no schematics, as often there are none for computer cards and motherboards. Then swap out (board jockey) has to occur which is very unsatisfying. I repaired a faulty mobo recently, only because the failed IC was heat sensitive and it was found with freeze spray, but I don't like it.

The other type of fault, which is even more diabolical and it is becoming more and more frequent, with the abolition of lead based solder, is tin whisker shorts.

The philosophical system of understanding a circuit and therefore which faulty part might be responsible for the signs of a fault, get tipped on its head. This is because the tin whisker can create links between sub-circuits to create entirely new circuit configurations that are not possible from the schematic and therefore produce weird and inexplicable faults.

So it is possible to have a faulty board in front of you on the bench, but not a single component on it is actually faulty. I had this in one of my 2465B scopes and it took me a week to find and fix it, one of those ones where you wonder if you are losing your mind as nothing is making sense:

http://worldphaco.com/uploads/TEKTRO...K_LEAKAGE..pdf

(For the OP: fortunately this sort of thing is very uncommon in old transistor radios)

Electrolyte from leaked caps on a pcb with high impedance circuitry can also do this sort of thing too with multiple conduction paths between tracks.

So there are always faults that cause extreme difficulty and frustration, no matter how experienced the technician is, or what fault finding techniques they practice.
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Old 28th Jul 2018, 8:31 am   #36
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Default Re: Hacker Sovereign 11

Stock faults were the bread and butter jobs, none stock ones were the interesting ones, or faults not seen before and then became stock ones were also the interesting ones.

Yes it was 6 years of half day release and two nights at a Tech plus learning on the job.

Knowing how the circuit works makes the job easier, less frustrating and more satisfying. Degree level knowledge is generally not required although those who have one I tip my hat to, something I could never have achieved.

I try to point posters to the information that Paul Stenning has written on another part of the web site, an excellent starter course.

If I have to fix anything I have not seen before, first job is always to find out the basics of how it works, at least there is a much better chance of a fix then.

It will be interesting to find out just which part or parts are faulty in the Hacker.
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Old 28th Jul 2018, 9:43 am   #37
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Default Re: Hacker Sovereign 11

Don't get too impressed with degrees, Frank. I've interviewed plenty of graduates who seemed to have no actual interest in the subject they'd qualified in, some seemed innumerate, some seemed to need telling when to think. The spectrum ranged all the way up to brilliant. I've explained to students that the piece of paper is needed to get their bum on a seat at an interview and then after that, they're on their own, expect to be grilled on their project work, set a puzzle to solve to see their thinking.

Degrees are not that difficult. I think most people, given good explanations, ought to be capable if they wanted one and had the time. The open university's material is very good indeed, and there are MIT lectures on video floating about the internet.

There's the sort of person who goes onto a degree course and comes out with a piece of paper only, then there's the one who thinks about it all and takes an interest. This one gets the piece of paper and a lot of knowledge. Some employers see only the paper, but it's the knowledge that confers the actual value.

I did a degree. A school friend did an HND at the same time. He had to do a lot more work. I was mystified somewhat. I saw how hard people on the TV course were worked. I have a lot of respect for them.

The degree seemed the easy way out and could have been if I'd just wanted the paper. But I wanted the knowledge and understanding. To get that I had to drive myself and I had to read books and effectively teach myself. Universities score brownie points for results... paper. No-one seems to check on what their product's capabilities are afterwards.

It's a weird world.

David
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Old 28th Jul 2018, 11:10 am   #38
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Quote:
Universities score brownie points for results... paper. No-one seems to check on what their product's capabilities are afterwards.
While it is a bit OT and won't help the OP fix his Hacker, this remark is very true. The situation I think deteriorated significantly with user pays education and the students becoming the paying customers that the University is then expected to qualify the majority of in return, thereby causing standards to slip.

Certainly the better electronic design & repair technicians I have met were always the ones who were interested in electronics themselves, with self directed learning and loved it. That is the real inspiration for success, in whatever field a person chooses.
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Old 28th Jul 2018, 11:28 am   #39
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Default Re: Hacker Sovereign 11

The last half dozen posts are fascinating but are not really relevant to fixing the Hacker. I wonder if they could be transferred to another thread called something like 'Approaches to Fault Finding'? I know such matters have been discussed in the past but a fresh airing of views does no harm. I'd be happy to contribute my thoughts from an amateur perspective.

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Old 28th Jul 2018, 2:14 pm   #40
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Default Re: Hacker Sovereign 11

all interesting stuff guys .Ok i have the radio out of its cabinet including the speaker [glad i took it out lots of fluff and other nasties in front of it ] I have tested it on various other sources both at high and low volume its working perfectly .I have just taken voltage measurements on all the transistors and i have measured the voltage at the junction of resistors 14/15.Rather than type them all out i have just photoed what i have written.All measurements were taken with the meter set as it is in the photo
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