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Old 5th May 2017, 6:48 am   #121
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Default Re: Sony HP-511 - Blowing Fuses

It is indeed a steep learning curve, but at least it is a learning curve, not a roadblock. There are so many little facts in the backs of the heads of those who've been at it a long time. We use this information without even thinking about it, and when trying to explain something forget to mention these facts.

In the majority of cases, small transistors have their legs coming out of the case in an isosceles triangular pattern. Look at the underside with the transistor rotated so that the long side of the triangle is to the bottom. the left wire is most often the emitter, the top one the base, and the right one the collector.

That 'majority' still leaves lots with other patterns and I often have to read numbers and hit the data books. Sometimes different makers used different pinouts for parts marked with the same type number... sometimes the legs were bent into the standard format, other times they just didn't bother.

Many times I've had to trace what a pin connects to just to be sure of which pin is which.

I'm an electronics designer by profession. That means I have to really, really understand how things work. It allows me to fault find just about anything, but it makes me glacially slow. I can see the thing working in my head and I can see the maths used to calculate component values. It makes me frustrated when I see things which weren'd designed as well as they could have been.

Other people come from a repair background and have built up amazing memories of common faults and repairs they've done. They may also have done troubleshooting courses presented by manufacturers on new models. These people are fast and leave the slow folk like me far to the rear. The slow folk come into their own when it is necessary to go exploring off-piste. On here you get a mixture of both types collaborating and together building insights which never happened back in the day. Plus, there's the 20-20 hindsight effect

Fixing something a bit beyond your normal limits requires certainty. Move slowly, check everything at least two ways. Because, when you make an error it affects everything you do afterwards, and that ruins your confidence. When you do get past the logjam you have one or two new tricks ready for the next time, and a boost in confidence.

The experienced gang have all been through this several times. They're watching your progress and thinking "He's coming along nicely". You're handling things quite a number of people run away from.

David
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Old 5th May 2017, 6:57 am   #122
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Default Re: Sony HP-511 - Blowing Fuses

I cross posted with Andy.

one characteristic of circuits like these power amplifiers with many transistors connected together with each one affecting the DC conditions of the others is that failure of one device can take others with it.

There is a trap you can easily get into. The old tried and true process of going through the parts and swapping each dead one you come across, then trying the circuit doesn't work reliably. You replace one part, try the set and another dead part destroys your new one in an instant. Without even any smoke! you think well that part's OK now, and move onto the next part... that's dead too, so replace it and try the set. This time the last part you replaced is dead and kills the new part. You are stuck in an infinite loop.

The cure is to find ALL the dead parts and not try the set until they ALL have been replaced. Sometimes it's easier to just replace the full set of semiconductors (and measure the Rs and Cs while the semis are out).

David
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Old 5th May 2017, 9:07 pm   #123
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Default Re: Sony HP-511 - Blowing Fuses

Hi Andy. I will wait to see what Dave stumbles across tomorrow but I will probably end up replacing all of the electrolytic caps for piece of mind anyway. Yes, I did test the forward diodes and compared the results with the others and these seemed to be ok from memory, desoldered from the board and the readings were in one direction. I remember you saying that the smaller electrolytic caps can be troublesome so I guess it's best to replace all of these considering how cheap they are.

David, I did try to measure the driver transistors using the 'top' pin as the base but I got some crazy readings and ended up measuring from the middle pin. I purchased a multimeter lead kit that included some of those spring loaded clips that Andy talked about a little while ago when we looked at injecting sinewaves into the poweramp and preamp boards. Something doesn't add up with these readings and I must have had Q506 & Q606 legs around the wrong way as the schematic stats outer pins for E and B. But then again, as you mentioned, this could be incorrect anyway... People avoiding working on this 'quasi-complementary' solid state amplifier does correlate with the response I've had from vintage repair shops before I posted here too.

I just want to check one thing here, running the set on the lamp limiter helps reduce the risk of blowing components but does it prevent the components from blowing to bits? Have I just been lucky in getting the set running on the LL? I always get worried turning it on in it's current state on the LL in fear of blowing bits. I think I read that the voltage is dropped from 240v~ to around 200v but I believe the set runs at 120v for the Japan market (I think Roger commented on that too).

One things for sure though, I've just purchased a new record for the collection so this set has to work!

Gareth
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Old 5th May 2017, 9:43 pm   #124
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Default Re: Sony HP-511 - Blowing Fuses

The lamp limiter will act to prevent high currenta and a burn up in the event of a short circuit forming across the main power supply. It honestly won't slow the destruction of transistors at all. It's a valid technique on valve power amps but it can give a false sense of protection on solid state stuff.

The mains voltage and even frequency varies around Japan. In some places it's officially 100v but can droop to 88v. Other places are 110 and 120v. Tokyo has 50Hz, Osaka has 60Hz

so they will have mains transformers with different primary taps for the different voltages, and different belt drive pulleys for the two frequencies.

People avoid working on solid state power amplifiers full stop. The things are perfectly manageable if you take a disciplined approach to them. They don't let people just jump in and start changing things willy nilly. That's expensive and often still doesn't fix the problem.

I built my hifi amplifier some years ago. The power amp's been working in my lounge since 1981. It uses 27 transistors per channel. Developing it stage-by stage meant arranging temporary feedback circuits to stand in for the missing stages, and having to bring up temporary supplies carefully and in order. No semiconductors were harmed in the development of this amplifier. It takes more care bringing up an unproven circuit than it does to fix one where you knew at least that the circuit could work. Prototypes don't give you that luxury. In doing one for yourself, you can at least fit protective elements to limit the propagation of destruction. In a commercial design, the accountants would be after you.

David
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Old 5th May 2017, 10:03 pm   #125
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Default Re: Sony HP-511 - Blowing Fuses

Thanks David, I didn't think the set was all that safe running on the LL...

Can you take a picture of the circuit board on that 27 transistor per channel power amp?! Why did you use 27 transistors? That sounds insane?! I know Roger mentioned a 200watt transistor amplifier than underpowered his speakers far less than a valve amplifier with 25% of it's power. I'm under the belief that transistor poweramps require high efficiency speakers whereas valve-amps have the 'clout' to move larger voice-coils? I presume this is the reason behind this?

Gareth
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Old 5th May 2017, 11:32 pm   #126
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Default Re: Sony HP-511 - Blowing Fuses

I'll take a photo when I'm back home.

Why 27 transistors?

Its input stage is a differential pair of transistors so that would be two, however, it rund two input stages in parallel. One an NPN pair, the other PNP. We're up to 4 transistors, now. Each of those transistors is cascoded with another one in its collector path. 8 transistors now. Then there are two transistors acting as constant current sources to bias the emitters of the above amplifiers. Total is 10 transistors.

The second stage, responsible for all of the voltage swing is like the first, but with different values and devices. that brings the total to 20.

transistor 21 is a Vbe multiplier to bias the following stages.

transistors 22 and 23 are emitter followers (PNP and NPN) which drive the output FETs.

the four remaining transistors are the complementary output devices, 2 FETs in parallel to get the current.

27 transistors.

There are two linear regulator chips to stabilise two supplies running 15v higher than the high power +55v supply and 15v below the high power -55v supply. Oh, and there are three bridge rectifiers and two transformers.

The other channel is a full duplicate.

It's a beast!

Why did I do it?

A colleague and myself were having a bit of fun, each designing amplifiers. Bill took a rather minimalist approach, and ever the loony I decided to use as many transistors as possible subject to the limitation that each had to do something useful. Great fun! Then Harry, the boss of thePCB layout folk was looking for something to use as a training exercise.... so boards were laid out and a few put through the standard process. Better and better!

The amp worked nicely and a number were made. Bill later became the product development manager at Linn. His amp was pretty good, too.

This was in an era before audiophilia distorted everything. No one took audio too seriously. It was an awful lot more fun!

The difference between valves and transistors is easy. The characteristic curves of valves are just that, curves not straight lines. They make a fair bit of distortion, but the smooth curve means that most of the distortion components added to the signal are lower harmonics and don't sound too bad. So valve amplifiers can be rather simple structures and their distortion is tolerated (celebrated in some circles!) The valves don't cut off quickly, or saturate hard, so they tend to not become too unpleasant if driven into the end-stops.

Transistors have curves too, but they are exponential shapes, putting more power into higher order harmonics. They have an abrupt cutoff point, and they also clip hard. These characteristics, if allowed to show, do not sound very good at all. So you have to stop them showing. You need feedback to linearise the exponential curve. you need to be careful to avoid that abrupt cutoff - it is the cause of "crossover distortion" and sounds awful. You must build a powerful amplifier so that it never gets driven into clipping because that also sounds nasty. You need headroom that a valve amp can get away without.

Do these things well and you have no need of valves. But not everyone did it well. Some people economised on power so they had amps which clipped on transients abd worse still could get stuck for a while at max voltage output Some people got feedback network design badly wrong. Some people didn't sort out crossover distortion.

There have been some truly gruesome transistor amplifiers designed over the years. Some aficionados interpret this as proof that all transistor amps are bad and that all future ones will always be bad. They seem prepared to fight to the death over this. Their loss!

An open mind and a sense of proportion keep you honest

David
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Old 6th May 2017, 6:07 am   #127
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Default Re: Sony HP-511 - Blowing Fuses

"It is indeed a steep learning curve, but at least it is a learning curve, not a roadblock." David's right, but as you learn more the curve gets less steep and you have enough knowledge that makes it a bit easier to learn more. Seven odd years ago when I joined the forum I didn't know what a capacitor did. I remember trying to test caps with the temperature probe on my meter.

As David says a LL won't guarantee something won't blow, but it's better than nothing. It can give you a bit of time to switch off and also gives a visual indication of a short and other conditions. Most folk use LL's with variac's, so the voltage and current is limited.

I think your misconception of a valve amp versus tranny amp's power stems from tranny amp manufacturer's in the past and now being on the whole a bunch of lying bar steward's. I was going to say they're economical with the truth, but the former is more accurate.

A watt is a watt whether it comes from a valve amp or tranny amp. It's the voltage on the output squared divided by the load. So measure the OP of your good channel in AC volts. If your playing music the reading will jump about a bit, take the average, square it, IE times it be itself and divide by 8 which is more than likely your speakers impedance.

If you do a search on here, there's loads of old threads on lot's of aspects of audio amplification and electronics. I was lucky when I landed 7 odd years ago to join a forum where replies to questions are based on sound electronic engineering facts and not myth's. Audiophiles are taken round the back for a good kicking.

I'm joking of coarse, same as when I said transistor amplifiers are the spawn of Satan. Good luck today round at Dave's, hope you get somewhere.

Andy.
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Old 6th May 2017, 2:14 pm   #128
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Default Re: Sony HP-511 - Blowing Fuses

Gareth’s mention of my experiments with valve versus solid state power dates to a time when a friend and I had an old Radford STA25 and a B&W Aura amp in the same room at the same time, rated 25W and 200W per channel respectively. So we took the opportunity to test them both into a pair of Radford Studio 60 transmission lines. Both amps sounded good but the old Radford seemed to accomplish everything with less ’effort’ and it sounded more ‘musical’ – all very subjective, I know. Nevertheless it all seemed a bit odd to say the least – surely it should have been the other way round?
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Old 6th May 2017, 5:15 pm   #129
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Default Re: Sony HP-511 - Blowing Fuses

There are many pitfalls to trying to judge things be ear. Left to their own devices, people turn up the volume to a level judged often by the amount of audible distortion. So amplifiers of low distortion get driven to higher outputs than those with more, which is hardly a level playing field, and then the nastier sort of distortion of the semiconductor amplifier gets criticised. Not in all cases of course, but you have to take a lot of care to make sure you aren't inadvertently leading yourself astray.

David
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Old 6th May 2017, 5:27 pm   #130
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Default Re: Sony HP-511 - Blowing Fuses

I thought I'd better update you guys on progress of this set...

Dave has been on the set for the best part of 6 hours today, not sure how he managed to stay focused for that time. Another top chap and naturally enthusiastic about electronics! He found a shorted transistor (Q505), removed it and checked the resistors and caps then fitted a replacement transistor. All seemed ok and he checked both outputs on a stethoscope (correct me if I'm wrong Dave). We hooked up the speaker to each channel and the audio was nice and clear. We measured power draw through the lamp limiter, all seemed good. Dave said he's a bit gutted that the repair was pretty straight forward. So we hooked it up to the mains and it blew both output transistors and started smoking a resistor... The set is now nicknamed 'bitch'.

We've called it a day for the minute but this thing sure doesn't want to give in easily.

Massive thanks to Dave so far for his effort and determination.

The saga continues.....
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Old 6th May 2017, 5:53 pm   #131
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Default Re: Sony HP-511 - Blowing Fuses

If Q505 was short circuit, there would be no bias on the output transistors and no quiescent current in them. This would make severe crossover distortion and it would not sound nice at all.

This may be one of those cases where it's just easier to put a set of transistors in as a oner.

David
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Old 6th May 2017, 7:10 pm   #132
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Default Re: Sony HP-511 - Blowing Fuses

Hi folks,
As Gareth said, after the initial fix, it looked to be working fine on the lamp limiter (at about 220V ac in, the lamp barely glowing) , driving a speaker and producing decent looking signals on both channels at several volts output (scope with 100+ MHz bandwidth). Tested with music and 50Hz - 5KHz sine wave. Job done ?

In a word, NO!

Powering up without the lamp limiter resulted 4 transistors in the trash : - both outputs, VAS and bias on the same channel.(2nd time, damn). I can now fully understand how patent Gareth is

Outputs are now 'hacked in' 44H11 (sans heatsink, better not connect the speaker!) with a ZTX450 doing the bias job and a 2N5551 as the VAS (which I did on a 30 min revisit). The amp is now 'working' again, this time on, a current limited PSU but it has some weird behavior ...

It works 'perfectly' giving 10V peak to peak at 1KHz but will sometimes go into 'silly mode' where the repaired channel amplitude decreases a bit, gets distorted on the -ve side and starts to pull a bit more current (with power supply current limiting and drops the voltage a bit). And its NOT oscillating. Seems to recover sometimes than after a few seconds the fault returns. I've not measured anything internal to amp yet. I am guessing that if this happens without some limiting then it will let out the smoke. Hopefully it should be possible to figure it out now that the fault is showing itself without any self destruction.

To be continued ...

dc

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Old 6th May 2017, 11:16 pm   #133
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Default Re: Sony HP-511 - Blowing Fuses

This Thread has gone off in so many (well intentioned) directions, I'm struggling to keep pace with he original issue...and even if it has been resolved....
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Old 7th May 2017, 5:42 am   #134
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Default Re: Sony HP-511 - Blowing Fuses

It needed looking at by someone with more experience. Oh no, 4 dead tranny's, a beam me up Scotty moment if ever there was one.

That's weird that both channels are going, is that PSU regulator part of the problem? You would hope it would clamp down on any over current conditions. If it's running away thermally is there any control Q or diode on the heatsink?

Do hope this gets fixed, it's been a saga. Andy.
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Old 7th May 2017, 7:09 am   #135
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Default Re: Sony HP-511 - Blowing Fuses

This set has got a large audience for its saga and it keeps producing cliff-hangers.
I expect either an American voice "Same time, same channel" or a notorious British burst of syndrums

Good luck

David
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Old 7th May 2017, 9:56 am   #136
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Default Re: Sony HP-511 - Blowing Fuses

One thing, there is a very large population of transistor amplifiers out there and the number is still increasing. Knowing how to handle them is an important skill, and it's well worth learning.

David
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Old 7th May 2017, 4:26 pm   #137
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Default Re: Sony HP-511 - Blowing Fuses

It is an intransigent little Sony, isn't it Dave? In my very limited experience of solid state amps a liberal dose of switch cleaner and the occasional judicious thump with the handle of a screwdriver has done the trick.....or not! This one is turning into an epic. It's great that you are involved and to quote the immortal Leslie Nielsen in 'Airplane'....we're all counting on you! But seriously - good luck and if I can help in any way, just let me know.
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Old 7th May 2017, 5:38 pm   #138
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Default Re: Sony HP-511 - Blowing Fuses

I believe Immanual Kant wrote an essay "On the inate animosity of inanimate objects"

He clearly knew a thing or two.

David
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Old 7th May 2017, 9:46 pm   #139
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Default Re: Sony HP-511 - Blowing Fuses

You've gotta chuckle, all this commotion over a 1972 solid state set that refuses to give in. I'm certain the Sony is in the best of hands now though. If anyone can figure this out it's Dave. I can't believe he's got that blooming thing running again so quickly. If it didn't have the sentimental value it would have been in the B1N months ago, following the #5 hammer treatment of course... Such is the sentimental value that I have to get it working, especially after hearing it playing properly again before it self destructed in it's now iconic fashion.

God help me!

Gareth

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Old 8th May 2017, 10:45 pm   #140
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Default Re: Sony HP-511 - Blowing Fuses

Here's a summary on the more recent history :

(1) Gareth had replaced a number of transistors but the thing still wasn't working and to aid diagnostics he had measured B-E voltages for both channels while powering with the lamp limiter.

(2) To me the voltages indicated the bias transistor was shorted C-E, so I replaced with something lying on the bench (BC108 if i recall, it would operate with ~2V and a few mA). Powered up (still on the lamp limiter) both channels of the amp looked OK now - driven to a decent voltage swing without load and to a lower output level driving a speaker. I was monitoring the main input voltage (after the lamp) and as it was 220V ac I thought it should be OK to apply mains, sans limiter

(3) Ooops, bad idea. 4 more dead transistors (same channel) in the 1/2 second it took for Gareth to turn it off again but no obvious reason why it failed. I see several possibilities (as scotty didn't get to the controls in time) ...

(a) Something happened during the much faster voltage ramp up - resulting in cross conduction, maybe a burst of oscillation.
(b) that last ~10% of voltage caused breakdown or oscillation.
(c) the transistors Gareth had fitted, I am somewhat dubious of the BD124's fitted and even the 2SC634 which should be the higher voltage 'A' version, although the other channel has the same plain jane 2SC634 !
(d) power supply fault at the last ~10% of voltage.
(e) something I've not thought of

(4) The 4 dead transistors are replace with some tougher replacements (as mentioned previously) and I am now power it up from a current limited supply. (Previously I mentioned some strange behavior but that was using the AUX input but it is NOT evident on the tape input with the pre-amp bypassed). The very brief look I've had, driven rail to rail without load, it looks fine - again ...

Next step, check I am getting the full rated voltage on the amp rails and then look for any hint of instability with a square wave / spectrum analyzer with a dummy load attached. I will also look at the start up characteristics with a storage scope but I don't see how I can simulate the full brutality of a mains startup AND protect the amp ...

I will also check the mains supply under full load, whatever that is !

dc
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