Okay guys time for an update.
Been a very rough several days here. AS of this day I am home and sick with the flu. A lot of other things not going well either. Father-in-law had two heart attacks back to back a few weeks ago and in the last 5 days he has had 4 mild heart attacks. he lives in another state. My wife is there with him but doctors are telling us that his heart is just plain getting ready to quit and he is to old to be doing any surgery on. Nothing much anyone can do. Just sitting and waiting now.
Now for the amp. There is some good news here. My 2SA1111 transistors came in. Yes they were indeed NOS. I had a choice to replace ALL or only the bad one and with things like they are at the moment I decided to go with the one that failed only. Installed the new transistor and set the bias. Connected a nice little preamp and played a little pink floyd and WHAMO. This thing rocks. WOW. I am impressed. I may just have to keep this thing. everything is balanced very well and the sound is phenomenal. I don't know what to say.
I guess the only real question I have at this point is should I be looking for the cause of the failure or do you think it was just the transistor failed on it's own?
And I can't do this without thanking all of you who jumped in and helped. I feel like I have learned a lot and this amp doesn't look so foreign to me now. Thanks again. It is greatly appreciated.
Been a very rough several days here. AS of this day I am home and sick with the flu. A lot of other things not going well either. Father-in-law had two heart attacks back to back a few weeks ago and in the last 5 days he has had 4 mild heart attacks. he lives in another state. My wife is there with him but doctors are telling us that his heart is just plain getting ready to quit and he is to old to be doing any surgery on. Nothing much anyone can do. Just sitting and waiting now.
Now for the amp. There is some good news here. My 2SA1111 transistors came in. Yes they were indeed NOS. I had a choice to replace ALL or only the bad one and with things like they are at the moment I decided to go with the one that failed only. Installed the new transistor and set the bias. Connected a nice little preamp and played a little pink floyd and WHAMO. This thing rocks. WOW. I am impressed. I may just have to keep this thing. everything is balanced very well and the sound is phenomenal. I don't know what to say.
I guess the only real question I have at this point is should I be looking for the cause of the failure or do you think it was just the transistor failed on it's own?
And I can't do this without thanking all of you who jumped in and helped. I feel like I have learned a lot and this amp doesn't look so foreign to me now. Thanks again. It is greatly appreciated.
Sorry to hear of your situation Terry 
The amp... I would think they just failed, I've seen this many times with Japanese devices and it seems to be just something peculiar to devices of that era. It would be worth checking/resetting the bias as a change of semiconductors may have altered it.
I really pleased the repairs were successful.
The amp... I would think they just failed, I've seen this many times with Japanese devices and it seems to be just something peculiar to devices of that era. It would be worth checking/resetting the bias as a change of semiconductors may have altered it.
I really pleased the repairs were successful.
Hi Terry,
0.6 what? Also, what is the resolution of your meter (I forget)?
You should have replaced all the output transistors, and the drivers. So that is all the output transistors for that one channel, and the driver transistors. The one blown PNP transistor stressed all of the NPN transistors and the driver. The PNP parts may have been driven through the base lead on the dead one, so they have been stressed too. They may appear to work okay, but the characteristics have changes now and they will likely fail later in time.
The rule of thumb for failed output stages is, replace all the outputs and also the first parts that test good. In your case that would be the driver transistors.
The bias shift with the new transistor was expected, but not to that degree. That was a 50% increase with a single transistor.
-Chris
0.6 what? Also, what is the resolution of your meter (I forget)?
You should have replaced all the output transistors, and the drivers. So that is all the output transistors for that one channel, and the driver transistors. The one blown PNP transistor stressed all of the NPN transistors and the driver. The PNP parts may have been driven through the base lead on the dead one, so they have been stressed too. They may appear to work okay, but the characteristics have changes now and they will likely fail later in time.
The rule of thumb for failed output stages is, replace all the outputs and also the first parts that test good. In your case that would be the driver transistors.
The bias shift with the new transistor was expected, but not to that degree. That was a 50% increase with a single transistor.
-Chris
Go back and read. In one post I was not advised to change ALL of them. In fact I was advised to only change the one. Or did I miss something? The resolution of my meter?.6 was a typo on my part. 6mv is what I set it to with a true rms meter. I also checked it with a second true rms meter. The manual says 6mv plus or minus 1MV. I got pretty darn close to 6. There is less than a quarter mv between them.
As I said I have had OTHER priorities to be taking care of. THIS was not on my list of important things to do. As of this morning my wifes father passed away. I will be busy for several days to come. I make mistakes. Everybody does.
As I said I have had OTHER priorities to be taking care of. THIS was not on my list of important things to do. As of this morning my wifes father passed away. I will be busy for several days to come. I make mistakes. Everybody does.
Hi Terry,
I'm really sorry to hear of your wife's father passing. Of course real life takes precedence over any hobby. I hope his death was more of a release from discomfort and not unexpected.
Yes, I thought you had a good meter. You're fine with that measurement. With that said, bias currents are never exact as they depend a great deal on temperature and supply voltage. So you will find the value seems to drift some. Don't be concerned. Having said that, I would be concerned if you find the bias has changed over 25%, Alarm bells should be ringing if it changes 50% or more. You have a fault in that case.
So once you are back, the rest of this post is just supposed to explain a bit. I did read the other posts, and I didn't see where you were advised to change only the defective one. That person is very definitely wrong and I am very sorry you were given that advice. You haven't any idea how many amplifiers I repair where the original repair only replaced one or a few outputs out of many. So, for future reference, please follow my advice which I gave along with the reasons for doing so. I feel like calling that other person an name, but that wouldn't be very professional - would it?
Yes, everyone makes mistakes. However, the advise you were given was made from a position of ignorance. That person shouldn't have said anything at all. So you didn't make the mistake, you were just a victim of mis-information.
The 500t is more reliable than most other brands. Properly serviced it should give you years of enjoyment. I should mention that there is talk of a Mark II version. Please do not follow that advice. The increase in running temperature for a couple extra watts of power (that you can't hear in the first place) is really not worth the extra stress on the amplifier. I have developed some changes that increase fidelity (lower distortion), but that is how I make my money. The changes in sonics are not massive, although they have been described that way. They mostly clean up the mids and highs a little while dropping background noise. All amplifiers always seem to have other issues as well, so this isn't something that would be done outside my lab. The circuit changes are minor so the original schematic still applies with some value changes.
To be clear, I am not recommending you send me your amplifier to work on, but rather to take care when you see other similar claims made by some others. The changes I make can be measured. Many other "updates" cannot be measured and they usually bring up the phrase that we can hear things that can't be measured. This is no longer true and a comment like that is normally made to sell expensive parts that you do not need.
I mention this only because it falls under the heading of false information.
Take care Terry. I was not criticizing you. I was only commenting on the error and why it wasn't true.
-Best, Chris
I'm really sorry to hear of your wife's father passing. Of course real life takes precedence over any hobby. I hope his death was more of a release from discomfort and not unexpected.
Yes, I thought you had a good meter. You're fine with that measurement. With that said, bias currents are never exact as they depend a great deal on temperature and supply voltage. So you will find the value seems to drift some. Don't be concerned. Having said that, I would be concerned if you find the bias has changed over 25%, Alarm bells should be ringing if it changes 50% or more. You have a fault in that case.
So once you are back, the rest of this post is just supposed to explain a bit. I did read the other posts, and I didn't see where you were advised to change only the defective one. That person is very definitely wrong and I am very sorry you were given that advice. You haven't any idea how many amplifiers I repair where the original repair only replaced one or a few outputs out of many. So, for future reference, please follow my advice which I gave along with the reasons for doing so. I feel like calling that other person an name, but that wouldn't be very professional - would it?
Yes, everyone makes mistakes. However, the advise you were given was made from a position of ignorance. That person shouldn't have said anything at all. So you didn't make the mistake, you were just a victim of mis-information.
The 500t is more reliable than most other brands. Properly serviced it should give you years of enjoyment. I should mention that there is talk of a Mark II version. Please do not follow that advice. The increase in running temperature for a couple extra watts of power (that you can't hear in the first place) is really not worth the extra stress on the amplifier. I have developed some changes that increase fidelity (lower distortion), but that is how I make my money. The changes in sonics are not massive, although they have been described that way. They mostly clean up the mids and highs a little while dropping background noise. All amplifiers always seem to have other issues as well, so this isn't something that would be done outside my lab. The circuit changes are minor so the original schematic still applies with some value changes.
To be clear, I am not recommending you send me your amplifier to work on, but rather to take care when you see other similar claims made by some others. The changes I make can be measured. Many other "updates" cannot be measured and they usually bring up the phrase that we can hear things that can't be measured. This is no longer true and a comment like that is normally made to sell expensive parts that you do not need.
I mention this only because it falls under the heading of false information.
Take care Terry. I was not criticizing you. I was only commenting on the error and why it wasn't true.
-Best, Chris
Thanks Chris, I went back and looked and I was wrong. I misinterpreted what someone else said as not changing anything else other than the bad one. Anywho my wife and I appreciate your kind comments. I am going to get back to this thing probably in the next week sometime and we can go further with it. As for the Mk II mods and such my thought on such things are if they are factory sanctioned then I don't have a problem with it. ANything else is questionable. If the thing has still got the factory stock setup and it works like it was designed then I leave them alone. And for now this things sounds fabulous so modding doesn't seem like such a benefit to me. Especially since I am not running a concert hall with it although it appears that I can obviously crank it pretty hard without any harm. I will see if I can include a video.
thanks again
Terry
thanks again
Terry
Hi Terry,
I'm glad you are continuing. Common sense can be your best friend, just as asking a question can save you a lot of grief later on. I'm pretty sure your amplifier will provide you years of good service while looking gorgeous in the process.
No, you really don't need a couple extra watts that actually amounts to a fraction of a dB more power.
-Chris
I'm glad you are continuing. Common sense can be your best friend, just as asking a question can save you a lot of grief later on. I'm pretty sure your amplifier will provide you years of good service while looking gorgeous in the process.
No, you really don't need a couple extra watts that actually amounts to a fraction of a dB more power.
-Chris
I want to thank everyone for their help. I completed replacing all the transistors in question on both sides and made my final settings and closed it up a few weeks ago. I have since been using it in my workshop on the days when I get a chance to be here. It sounds fabulous. Most of my time has been spent lately visiting my dad in another state as he has been very ill. Alas I am already on another project that is going to be yet another headache. Anybody know anything about PS Audio 100C amps? I got my hands on one and found out first thing that the schematics and tech manuals are non existent. I realized someone had modded the hell out of this thing trying to permanently bridge both sides. It is a mess inside and one side is not working. It appears that this thing was built as two mono blocks inside and someone tried to make major changes. The boards look like crap and I am thinking seriously about sending this to the dumpster and sell off the few usable parts that I can. Thanks again for all of your help. I may start another topic for this PS Audio. I dunno yet. Thanks again.
Hi Terry,
If it was me in your shoes, I would sell the few bits I could and scrap the rest. You may find that the chassis as it is might suit a DIY amplifier. Then you have most of your expensive stuff already (case & transformer).
When a repair or modification was attempted, but not successful, it means the "tech" was in panic mode at some point. That person would then do things they normally wouldn't, so you will probably find some things done that don't make any sense at all. So at the minimum, strip and clean the chassis. Then take stock of the other stuff to see what can be salvaged. I can't see you winning with this as a repair, and if the PCBs are in rough shape I would question reliability.
Best, Chris
If it was me in your shoes, I would sell the few bits I could and scrap the rest. You may find that the chassis as it is might suit a DIY amplifier. Then you have most of your expensive stuff already (case & transformer).
When a repair or modification was attempted, but not successful, it means the "tech" was in panic mode at some point. That person would then do things they normally wouldn't, so you will probably find some things done that don't make any sense at all. So at the minimum, strip and clean the chassis. Then take stock of the other stuff to see what can be salvaged. I can't see you winning with this as a repair, and if the PCBs are in rough shape I would question reliability.
Best, Chris
Thank you kindly Anatech. Yes the PCBs are in horrible shape. On the other hand I like your suggestion of building a DIY amp. I would not know where to start. I am sure there are kits out there. I guess I would just have to research this. On that note I am thinking two mono blocks of say 250 watts each would be killer. But I am definitely open for any ideas. Got anything in mind? Something a little unusual or different? Something that would definitely be a conversation piece? I like the unusual.
Hi Terry,
I seriously question the need or desire for 250 watts per channel in mono blocks. There are any number of excellent stereo 250 watts per channel type power amps. My Marantz 300DC (150 wpc) will bottom the drivers of my PSB Stratus Gold speakers at about the same time it clips. Okay, so the Marantz puts out somewhat more power than it is rated at, but I never run the system anywhere near those levels.
You could build a stereo Honey Badger, or some of the other amplifiers now in threads. I'm sorry that I can't remember their names, but there is some darned good stuff available.
The first step you should take is to find out what supply voltage you have. That will determine how much power you can hope for. Don't get too hung up on power output. Once you clear 150 watts, you're really in an area where speakers have short lifetimes.
You know what would be really cool, and you only need a fraction of the power? Go active with the crossover, and a separate amplifier for each driver. Without the passive crossover the speakers are a lot more efficient - and you can use the amplifier's damping full on each driver. You won't ever go back to a passive crossover after that!
First, look at that transformer, or power it up with the amps disconnected to see what your voltages are.
-Chris
I seriously question the need or desire for 250 watts per channel in mono blocks. There are any number of excellent stereo 250 watts per channel type power amps. My Marantz 300DC (150 wpc) will bottom the drivers of my PSB Stratus Gold speakers at about the same time it clips. Okay, so the Marantz puts out somewhat more power than it is rated at, but I never run the system anywhere near those levels.
You could build a stereo Honey Badger, or some of the other amplifiers now in threads. I'm sorry that I can't remember their names, but there is some darned good stuff available.
The first step you should take is to find out what supply voltage you have. That will determine how much power you can hope for. Don't get too hung up on power output. Once you clear 150 watts, you're really in an area where speakers have short lifetimes.
You know what would be really cool, and you only need a fraction of the power? Go active with the crossover, and a separate amplifier for each driver. Without the passive crossover the speakers are a lot more efficient - and you can use the amplifier's damping full on each driver. You won't ever go back to a passive crossover after that!
First, look at that transformer, or power it up with the amps disconnected to see what your voltages are.
-Chris
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