It was the Alpha 440 / 450 I was referring to. I didn't do warranty on them but I sure did get a lot them in my shop.
Was it you wahab that mentioned throwing amps out the window?
David.
Was it you wahab that mentioned throwing amps out the window?
David.
Yes, but it was only an instantaneous thought at the time,
which was not followed by any action, fortunately.
It wasn t this amp that was at risk, as i mentionned it, i didn t
even bother trying to repair the NIKKO, i did simply replace the original
PCBs with an amp that i designed on the fly...
Heck, i rarely saw as much low power trannies in a power amp,
while there was only one pair of TO3 output devices per channel,
quite odd considering the relatively high output power..
Oh maybe it was the Beta series then. My memory of them is fading. Beta 400 I think is what's haunting me.
David.
David.
Decisions, decisions. Obviously it would be cheaper and easier to replace just the bad transistor, provided I can find the original Toshiba part (thanks for the lead, David).
But isn't the conventional wisdom that if one goes bad, they have all been stressed and should all be replaced?
In any case, I'll continue to reassemble the input board as discussed earlier while I figure out the next step.
But isn't the conventional wisdom that if one goes bad, they have all been stressed and should all be replaced?
In any case, I'll continue to reassemble the input board as discussed earlier while I figure out the next step.
Coincidently enough, I have an Alpha 220 that I use as a sub-amp. I was thinking of selling it as soon as this Adcom is running again, and you guys have convinced me that is the right thing to do. It never sounded that good to me. Okay, but not great.
FWIW, and while we're off-topic, my favorite sounding amp is my Luxman. I understand (thanks to this thread) that they are maybe un-necessarily complex, but I love their look, their build quality and above all their sound. When I build my own amp, I will look for a design that sounds similar.
FWIW, and while we're off-topic, my favorite sounding amp is my Luxman. I understand (thanks to this thread) that they are maybe un-necessarily complex, but I love their look, their build quality and above all their sound. When I build my own amp, I will look for a design that sounds similar.
When I did repairs in my shop, if the majority of the outputs were blown in an amp then I would replace all the outputs. But one or two blown, then just that as long as the others were reasonably matched and not leaking. It's your choice. In an amp as old as that one I might replace all the TRs and any electrolytic caps excluding the PW mains filters if they test ok.
If I were selling the amp I would replace only what's necessary, but you're planning on keeping this amp aren't you?
David.
If I were selling the amp I would replace only what's necessary, but you're planning on keeping this amp aren't you?
David.
Transistors can wear out over time, become more noisy. One of the more common wears is from thermal stress on the internal leads connecting to the package pins. These leads can break or become intermittent in their connection. Usually the problem shows up when the part is heated. This problem is more common with ICs like the STK packs but I have found it with transistors.
David.
David.
David.
David.
Hi Fred,
This is only true if the output stage blows up. This is not the case for you. I would recommend you replace the one transistor only. I would recommend the same thing if the amp was in my shop for service in this case.
Luxman amplifiers normally sound pretty darn good. My favorite set was the M02 and C02 combination power and preamp. I do have to correct a false impression though. Luxman amplifiers (or anything else for that matter) are not overly complicated. They are no more involved than most other good quality brands. You want complicated? Yamaha. Those guys can take a simple circuit and blow it way up in complexity. The tuners in most of the "R" series receivers used two microprocessors .... TWO! Some muting circuits were more complicated than the gain stages in some preamplifiers. There are other excellent examples of designs that seem to be complicated for the sake of complexity, but I wouldn't put Luxman in that category. Hmmm, Carver stuff can be complicated too, but there is a reason for this.
Basing your design on a Luxman, Marantz or Cyrus would be a good start. All of these will provide exceptional sound quality.
-Chris
Firstly, have you even tried to remove, clean and retest this transistor yet? We don't know for sure if it's defective or not yet.
This is only true if the output stage blows up. This is not the case for you. I would recommend you replace the one transistor only. I would recommend the same thing if the amp was in my shop for service in this case.
Your Alpha 220 is not an amplifier that has any known problems. They are pretty reliable actually, and for the price, they are hard to beat. Yes, they sound a little odd. Since I have some (and Alpha 230 also), I'll eventually have a look and eliminate this oddity. The problem might even be the DC servo amp circuit.
Yet another brand I did warranty work for.
Luxman amplifiers normally sound pretty darn good. My favorite set was the M02 and C02 combination power and preamp. I do have to correct a false impression though. Luxman amplifiers (or anything else for that matter) are not overly complicated. They are no more involved than most other good quality brands. You want complicated? Yamaha. Those guys can take a simple circuit and blow it way up in complexity. The tuners in most of the "R" series receivers used two microprocessors .... TWO! Some muting circuits were more complicated than the gain stages in some preamplifiers. There are other excellent examples of designs that seem to be complicated for the sake of complexity, but I wouldn't put Luxman in that category. Hmmm, Carver stuff can be complicated too, but there is a reason for this.
Basing your design on a Luxman, Marantz or Cyrus would be a good start. All of these will provide exceptional sound quality.
-Chris
Well, at this point I've spent more on shipping alone for new parts than I could probably get from selling it, so I guess I'm keeping it!
That and the fact that 2SD424's (what's in my amp) are hard to find makes me think I should just bite the bullet and replace/re-build both output boards with all new semis. Are we in agreement that On Semi MJ15022G and MJ15023G are a suitable substitute?
In the meanwhile, I'll reconnect everything (except the bad 424) on the output boards, reassemble the input board and get on with testing.
Chris, you have me oscillating as bad as this amp! I will definitely pull,clean and test Q17 to verify it's bad.
Initial googling has not turned up a source for these other than ebay, which I don't trust. I have a note in to Main Electronics that David linked to above.
So, plan A, replace just Q17 (assuming it is actually bad). If I can't locate a replacement 2SD424, go to Plan B and replace all the output semis with a substitute.
This Adcom was driven by a Luxman C02! I've been trying to decide if it would be worth the trouble to replace all the 'lytics in it, etc. Or would a 5C50 be more worth my time and effort?
Last edited:
Hi wahab,
With the standards of the time, that output stage was not low powered at all. From memory, those NEC transistors were rated at 200 watts dissipation and there was no substitute available at such a high power and the same case. This in an amp rated at 100 watts per channel into 8 ohms.
Hi David,
Those Alpha 440 and 450 amplifiers were not reliable. I think I repaired a couple (they even stayed fixed!), but after that I refused to fix them. In my estimation, those were dangerous amplifiers. Nothing was more dangerous than a Proximity (from Quebec) though. A Bryston 4B was pretty irresponsibly designed as well, no protection at all, and they did blow (not something that Bryston would admit to at the time).
I'm sure your design was pretty good, but I don't believe you did the customer a service by swapping it out. Not unless that customer was attempting to use a consumer home amp as a DJ amplifier. I can see why that wouldn't work out. BTW, they were priced low even then. The guy must have been cheap, no other explanation.
Some transistors get noisy or leaky (or both) over time, but I suspect that there were contaminates on the die when they were packaged. High current and reverse E-B bias with current flow can damage these parts as well. With the exception of some crappy TO-3 packages, I haven't seen loose leads on power transistors.
-Chris
That was an Alpha II. It used one complimentary pair of 2SD555 and 2SB600, which were about the highest rated Japanese audio transistor at the time. These were extremely reliable amplifiers, and they sounded better than the amps that came after. I repaired the odd one long before I got the warranty contract for that brand.
With the standards of the time, that output stage was not low powered at all. From memory, those NEC transistors were rated at 200 watts dissipation and there was no substitute available at such a high power and the same case. This in an amp rated at 100 watts per channel into 8 ohms.
Hi David,
Those Alpha 440 and 450 amplifiers were not reliable. I think I repaired a couple (they even stayed fixed!), but after that I refused to fix them. In my estimation, those were dangerous amplifiers. Nothing was more dangerous than a Proximity (from Quebec) though. A Bryston 4B was pretty irresponsibly designed as well, no protection at all, and they did blow (not something that Bryston would admit to at the time).
I'm sure your design was pretty good, but I don't believe you did the customer a service by swapping it out. Not unless that customer was attempting to use a consumer home amp as a DJ amplifier. I can see why that wouldn't work out. BTW, they were priced low even then. The guy must have been cheap, no other explanation.
Rare with transistors, although more common with remarked and fake devices. The reason that the STK thick film modules tended to go open was the attachment to the substrate. Then there was a run of defective STK-050 (?) parts where the leads were poorly bonded. These showed up a lot in the Marantz products in the early Philips days. Those were dark days indeed. Once TC Electronics got the line, it was all over and I rejected the contract. Too bad as I really like the older stuff from Marantz, the new stuff is really good too.
Some transistors get noisy or leaky (or both) over time, but I suspect that there were contaminates on the die when they were packaged. High current and reverse E-B bias with current flow can damage these parts as well. With the exception of some crappy TO-3 packages, I haven't seen loose leads on power transistors.
If you do a job, your name is on it. Always to a proper and responsible repair job when working on something. Otherwise, sell it as-is. I'm really tired of cleaning up previous work!
-Chris
Hi Fred,
That sounds good. Don't be in a rush though.
I mentioned you should check that transistor earlier, you may have missed that comment.
Do some searching on the 'net for outputs. Another source might be a scrapped amp or receiver, you could take a used one from a channel that wasn't blown.
-Chris
That sounds good. Don't be in a rush though.
I mentioned you should check that transistor earlier, you may have missed that comment.
Do some searching on the 'net for outputs. Another source might be a scrapped amp or receiver, you could take a used one from a channel that wasn't blown.
-Chris
My suggestion to even consider replacing just one was based on the idea of saving some money, however I didn't consider what you've spent on test equipment etc. And if you do replace just one it is important to build some confidence in the ones you don't replace. Given the power and the damage it could do to speakers it is something to think about. Did it already take out a speaker?
One issue is getting the new parts and being sure that they are not fakes. We cannot be sure that it is just one bad part until you do full voltage testing on the others, that might give you a better feel for what to do next. That transistor probably failed because this amp runs with high rail voltages which puts the devices high up on the SOA curve where secondary breakdown comes into play. They are 150W devices so even with no temp or secondary breakdown derating we have Imax = 150/80 = 1.9A per device @ 80V. 1.9 * 4 = 7.6A and the fuse is 6A but will pass far more for many milliseconds. That transistor might have had the highest beta so it took more of the hit, or it might have not aged as well as the others, hard to say. Amazing how four 15A devices get derated so far. But even with transistors the numbers are marketing numbers, the 150W is at 25deg C not even a very hot summer day. You'd have to chill the parts on a hot day to meet the 150W rating.
One issue is getting the new parts and being sure that they are not fakes. We cannot be sure that it is just one bad part until you do full voltage testing on the others, that might give you a better feel for what to do next. That transistor probably failed because this amp runs with high rail voltages which puts the devices high up on the SOA curve where secondary breakdown comes into play. They are 150W devices so even with no temp or secondary breakdown derating we have Imax = 150/80 = 1.9A per device @ 80V. 1.9 * 4 = 7.6A and the fuse is 6A but will pass far more for many milliseconds. That transistor might have had the highest beta so it took more of the hit, or it might have not aged as well as the others, hard to say. Amazing how four 15A devices get derated so far. But even with transistors the numbers are marketing numbers, the 150W is at 25deg C not even a very hot summer day. You'd have to chill the parts on a hot day to meet the 150W rating.
Last edited:
Hi Chris
'If I were selling the amp I would replace only what's necessary, but you're planning on keeping this amp aren't you? '
"If you do a job, your name is on it. Always to a proper and responsible repair job when working on something. Otherwise, sell it as-is. I'm really tired of cleaning up previous work!"
Chris by no means was I suggesting doing shotty job just because one is planning to sell the unit. I took a lot of pride in the work I did and in the work I do. And like yourself I was the tech that everyone else sent all the stuff they couldn't or wouldn't repair. So I can totally relate to what you're saying.
All I meant was, why do all the updates and improvements you would do for yourself if your planning on selling the amp? why not get it working properly and let the next guy decide what he wants to do with it. Unless of course it's you business to do updates.
Although it is rare to find lead failure in transistors, I have had to-92 and to-3 packages fail this way. I am aware of the problem with STK 050 but I have found quite a number of STK numbers with lead failure.
David.
'If I were selling the amp I would replace only what's necessary, but you're planning on keeping this amp aren't you? '
"If you do a job, your name is on it. Always to a proper and responsible repair job when working on something. Otherwise, sell it as-is. I'm really tired of cleaning up previous work!"
Chris by no means was I suggesting doing shotty job just because one is planning to sell the unit. I took a lot of pride in the work I did and in the work I do. And like yourself I was the tech that everyone else sent all the stuff they couldn't or wouldn't repair. So I can totally relate to what you're saying.
All I meant was, why do all the updates and improvements you would do for yourself if your planning on selling the amp? why not get it working properly and let the next guy decide what he wants to do with it. Unless of course it's you business to do updates.
Although it is rare to find lead failure in transistors, I have had to-92 and to-3 packages fail this way. I am aware of the problem with STK 050 but I have found quite a number of STK numbers with lead failure.
David.
Hi David,
I figured you do good work, but remember we have rank amateurs reading these forums. I try to make sure the message is clear all the time. I'm pretty sure you'd agree with that!
As far as going nuts on an amp you plan to sell, completely agree. Do whatever repairs are needed, but do them properly. Doing a bunch of "improvements" on an item you are planning to sell doesn't make any sense, as you've pointed out.
I've only found TO-92 transistors that have gone intermittent and / or noisy. I haven't seen any with loose leads unless the case is also cracked (that's where the magic smoke came out). I haven't serviced many STK based things as of late, but you are right about other STK modules. All those voltage amps in Yamaha equipment, I forgot about those. I have to admit that I haven't seen as many STK modules as you have.
-Chris
I figured you do good work, but remember we have rank amateurs reading these forums. I try to make sure the message is clear all the time. I'm pretty sure you'd agree with that!
As far as going nuts on an amp you plan to sell, completely agree. Do whatever repairs are needed, but do them properly. Doing a bunch of "improvements" on an item you are planning to sell doesn't make any sense, as you've pointed out.
I've only found TO-92 transistors that have gone intermittent and / or noisy. I haven't seen any with loose leads unless the case is also cracked (that's where the magic smoke came out). I haven't serviced many STK based things as of late, but you are right about other STK modules. All those voltage amps in Yamaha equipment, I forgot about those. I have to admit that I haven't seen as many STK modules as you have.
Oh yeah! That's for certain.
-Chris
Chris
I'll take it as moderation then. After all that is one of you functions here.
I do sense from Fred that there is a definite comfort level for him, since this is his first power amp repair. I totally understand where he is coming from. I think, and Fred do correct me if I wrong, that he may be more confident with changing all the outputs. That way there is no doubt.
No doubt the shipping cost are racking up as well and it certainly is more economical to ship a set of outputs than just one.
David.
I'll take it as moderation then. After all that is one of you functions here.
I do sense from Fred that there is a definite comfort level for him, since this is his first power amp repair. I totally understand where he is coming from. I think, and Fred do correct me if I wrong, that he may be more confident with changing all the outputs. That way there is no doubt.
No doubt the shipping cost are racking up as well and it certainly is more economical to ship a set of outputs than just one.
David.
David, it's true I have a definite comfort level, and that level is defined by following the opinion of the FAR more experienced techs who are helping me, yourself included.
I did remove, thoroughly clean and re-test Q17. Same results, 10 u-amps of C-E leakage.
So, I will follow everyone's advice and replace just Q17. I ordered a couple of 2sd424's from MCM. (Pete, I must have somehow missed them before, or they came back in stock.)
Meanwhile, I'll get things put back together for output testing that Pete recommended (unless you no longer think it necessary, Pete): all boards reconnected normally, Q1 and Q2 pulled, Q17 pulled, T1 replaced with a jumper wire, for ease of disconnection.
For the record, I don't plan on selling this amp, provided I can fix it. I only mentioned my shipping costs as a way of making the point that I've got so much time and money in the thing at this point that selling it wouldn't begin to recover the costs. That's okay. I'm looking at the expenses as "tuition" rather than repair costs! If at the end of all this, I end up with useful education/experience, a working amp and a better equipped bench, it's well worth a few hundred bucks.
I'd be suspicious about these. Perhaps you could post a wanted ad in the swap meet on this forum to look for someone here who has known, old stock, non-counterfeit Toshiba 424's. This one is often counterfeited.
Steve.
Hi Fred,
I'm not sure if they confirmed that they are Toshiba's for you, but there are now other sources that I have no experience with:
http://audiolabga.com/pdf/2SD424.pdf
I would not trust them.
I have a doner amp, that I might be able to pull at least one from for you, just let me know. This amp was a friends, that he used in his home and did not really push hard. He had the local shop fix it several times and they could not seem to get it right. One channel has always been fine on it so I'd pull from that one. I plan to pull a few myself just to have a few to measure. I have to check if it still has originals or substitutes, I seem to recall them being Toshibas.
Let's see what you get from MCM if Toshibas then you might be good to go.
I'm not sure if you are aware of the counterfeit issue:
Counterfeit Transistors
One of my main clients is getting deep into component authentication. They are probably the best lab in the world. They have several types of X-ray equipment, decapsulation, and on. One simple test that remarked parts often fail is to see if the markings come off with acetone, there was one other standard solvent that they used, I can't remember at the moment what it was. This was used for IC type packages not sure if transistor markings are as permanent. I'll find out since this is good to know.
There was a recent cover page article in one of the business magazines about counterfeit parts that made in into Military equipment.