You're very welcome - so far so good.
Couple of issues:
First, the working channel. Not burst your bubble, but I'm still a bit suspicious of that channel. Between the part that was disconnected, the fried resistor on the RC network and the mixed parts, it makes me a bit nervous. While I'm very glad it's working, I'm not quite ready to say put it into service. It is possible to have a bad output transistor and still have the channel working.
You posted that you "measured no DC at the input". I need you to check for DC at the output (speaker) terminals with no input and only the meter hooked to the outputs. You will want to set your meter to DC Mv setting.
Is there any chance that you know someone with a scope and signal generator that you might be able to borrow? I would give anything to see if that channel is really clean.
Again, not meant to burst your bubble, I just prefer to be cautious.
Perhaps Nelson knows a few places to have you test with your meter that will give us a better idea if that channel is truly stable and safe.
Regarding ordering outputs, I would try very hard to source all Motorola parts if you can find them.
Depending on the price, it might make more sense to switch both channels to the MJ 150022/24 series of outputs. They're readily available and will work just fine. For drivers, MJE 15030/31. I would do both channels so they're all matched and save the good outputs as spares for your other amp.
The other possible source for outputs would be Jon Soderberg. If he's switching out all of them in amps with one blown channel to the newer MJ's, he might have good original units that he'd be willing to sell to you. It couldn't hurt to call and ask. He's a good guy! Also, inquire to see what he recommends for replacement drivers and outputs, just to be sure we're on the right track.
Again, I'd source original Motorola from the same lot if at all possible.
Don't forget while you're ordering that you're also going to need new insulators and silicone grease for mounting the outputs. You can either go with mica insulators or some of the newer high tech greaseless type.
Couple of issues:
First, the working channel. Not burst your bubble, but I'm still a bit suspicious of that channel. Between the part that was disconnected, the fried resistor on the RC network and the mixed parts, it makes me a bit nervous. While I'm very glad it's working, I'm not quite ready to say put it into service. It is possible to have a bad output transistor and still have the channel working.
You posted that you "measured no DC at the input". I need you to check for DC at the output (speaker) terminals with no input and only the meter hooked to the outputs. You will want to set your meter to DC Mv setting.
Is there any chance that you know someone with a scope and signal generator that you might be able to borrow? I would give anything to see if that channel is really clean.
Again, not meant to burst your bubble, I just prefer to be cautious.
Perhaps Nelson knows a few places to have you test with your meter that will give us a better idea if that channel is truly stable and safe.
Regarding ordering outputs, I would try very hard to source all Motorola parts if you can find them.
Depending on the price, it might make more sense to switch both channels to the MJ 150022/24 series of outputs. They're readily available and will work just fine. For drivers, MJE 15030/31. I would do both channels so they're all matched and save the good outputs as spares for your other amp.
The other possible source for outputs would be Jon Soderberg. If he's switching out all of them in amps with one blown channel to the newer MJ's, he might have good original units that he'd be willing to sell to you. It couldn't hurt to call and ask. He's a good guy! Also, inquire to see what he recommends for replacement drivers and outputs, just to be sure we're on the right track.
Again, I'd source original Motorola from the same lot if at all possible.
Don't forget while you're ordering that you're also going to need new insulators and silicone grease for mounting the outputs. You can either go with mica insulators or some of the newer high tech greaseless type.
Well, Barchetta, it seems like you've made a lot of progress.
🙂
I recommend soldering up the unsoldered resistor on the
working channel and replacing the burned resistors. If you
remove the broken channel you can use the working channel
to gather some information.
Try measuring the case voltages of all the output devices and
also the output DC.
😎
🙂
I recommend soldering up the unsoldered resistor on the
working channel and replacing the burned resistors. If you
remove the broken channel you can use the working channel
to gather some information.
Try measuring the case voltages of all the output devices and
also the output DC.
😎
Okay on the insulators.. I have heat sink compound.. can I use that? Or do I need grease?
I measure .027v dc at the output with no input connected.. is this bad? I'd measure my good amp but I dont even want to touch it! 🙂
On the transistors.. ya know; Id much rather stay 100% stock.. that way I can get advice and there is not a variable there.. so I will try and source them.. so neither of those links I sent you is Motorola.. thats why I asked.. I guess I will have to call around.. I didnt' get time today.. and I am sure everything is closed now.. so maybe tomorrow.
I knew this part was gonna be a pain in the butt.. but it will be worth it I am sure.
Mr. Pass: I did resolder that resistor.. as Steve Mentioned (btw my name is Joe).. we are not 100% sure its working.. it plays nice thru an old speaker.. but I am still way too afraid to connect to my vandersteens.. need to do some more testing.. I am going to try and find a scope per Steve and maybe he can help me understand the condition.
Steve; I think I felt all the transistors except the very bottom ones.. (which includes the one that has the emitter resistor disconnected..) would that be a "interesting".. I gotta think if one is cold its "bad"?
I measure .027v dc at the output with no input connected.. is this bad? I'd measure my good amp but I dont even want to touch it! 🙂
On the transistors.. ya know; Id much rather stay 100% stock.. that way I can get advice and there is not a variable there.. so I will try and source them.. so neither of those links I sent you is Motorola.. thats why I asked.. I guess I will have to call around.. I didnt' get time today.. and I am sure everything is closed now.. so maybe tomorrow.
I knew this part was gonna be a pain in the butt.. but it will be worth it I am sure.
Mr. Pass: I did resolder that resistor.. as Steve Mentioned (btw my name is Joe).. we are not 100% sure its working.. it plays nice thru an old speaker.. but I am still way too afraid to connect to my vandersteens.. need to do some more testing.. I am going to try and find a scope per Steve and maybe he can help me understand the condition.
Steve; I think I felt all the transistors except the very bottom ones.. (which includes the one that has the emitter resistor disconnected..) would that be a "interesting".. I gotta think if one is cold its "bad"?
Hi Joe,
Output DC looks good. I can't help but think that the tech must have pulled off this thing before he was finished.
Heatsink compound is what you want. You'll want to order mica insulators then.
I found this post from Nelson that I thought you might need for reference. If you can get the original parts great. If not, I'd replace them all in both channels with the MJ series.
http://www.diyaudio.com/forums/showthread.php?threadid=34275
"Steve; I think I felt all the transistors except the very bottom ones.. (which includes the one that has the emitter resistor disconnected..) would that be a "interesting".. I gotta think if one is cold its "bad"?"
Your assumption would be correct as a failed device would no longer be resisting current flow and would either be a dead short or open. Either way, it wouldn't be generating much (if any) heat.
Usually outputs fail as a dead short not an open; although I've seen both. If you had one with a short, you'd see lots of DC at the output and your speaker would have already smoked. Not saying they can't fail open, just not usually in my experience.
Do me a favor and be very careful when "feeling" the transistors. When the unit is on, those transistor cases have ~60 volts on them and the heatsinks are grounded. Be very, very careful. I can understand your warmth test and it does make sense, however the idea here is to make sure you are here for continued testing tomorrow.
Also just for reference, when working on an amp that's powered up, if you're going to be poking around always try to only touch things with only one hand at a time. Should you get shocked, if you're using only one hand, it can bite but that's all. But, lets say you had one hand on a heatsink and another touching transistor cases for example, then if you got shocked it would send current across your heart. This would not be good thing...
I'd much prefer you be using an insulated temperature probe or a test lead than your finger. This is respectfully submitted as serious food for thought. (and yes, I've done the same thing)
Good progress so far!
Output DC looks good. I can't help but think that the tech must have pulled off this thing before he was finished.
Heatsink compound is what you want. You'll want to order mica insulators then.
I found this post from Nelson that I thought you might need for reference. If you can get the original parts great. If not, I'd replace them all in both channels with the MJ series.
http://www.diyaudio.com/forums/showthread.php?threadid=34275
"Steve; I think I felt all the transistors except the very bottom ones.. (which includes the one that has the emitter resistor disconnected..) would that be a "interesting".. I gotta think if one is cold its "bad"?"
Your assumption would be correct as a failed device would no longer be resisting current flow and would either be a dead short or open. Either way, it wouldn't be generating much (if any) heat.
Usually outputs fail as a dead short not an open; although I've seen both. If you had one with a short, you'd see lots of DC at the output and your speaker would have already smoked. Not saying they can't fail open, just not usually in my experience.
Do me a favor and be very careful when "feeling" the transistors. When the unit is on, those transistor cases have ~60 volts on them and the heatsinks are grounded. Be very, very careful. I can understand your warmth test and it does make sense, however the idea here is to make sure you are here for continued testing tomorrow.
Also just for reference, when working on an amp that's powered up, if you're going to be poking around always try to only touch things with only one hand at a time. Should you get shocked, if you're using only one hand, it can bite but that's all. But, lets say you had one hand on a heatsink and another touching transistor cases for example, then if you got shocked it would send current across your heart. This would not be good thing...
I'd much prefer you be using an insulated temperature probe or a test lead than your finger. This is respectfully submitted as serious food for thought. (and yes, I've done the same thing)
Good progress so far!
Advice understood and may or not be used.. 🙂 Probably not. 🙂 Cept; I was taught one thing a LONG time ago when in a dangerous situation.. ALWAYS one hand behind on your back.. so thats my rule. 🙂
Okay; so what adjustments do I need to make if I install MJ15023? and I forget what the two designations are.. I'll search it.. but okay.. I am game.. especially since I found a thread where I read about lots of FAKE motorola parts!
Damn I wanted to order today.. but want to know how hard it will be to retrofit these... hope someone is around...
EDIT: reading Steves post again I guess I need drivers too? 4 each side right?
EDIT AGAIN: and I see its MJ 150022/24 so..12 MJ 150022 and 12 MJ 150024...
just being sure.
Okay; so what adjustments do I need to make if I install MJ15023? and I forget what the two designations are.. I'll search it.. but okay.. I am game.. especially since I found a thread where I read about lots of FAKE motorola parts!
Damn I wanted to order today.. but want to know how hard it will be to retrofit these... hope someone is around...
EDIT: reading Steves post again I guess I need drivers too? 4 each side right?
EDIT AGAIN: and I see its MJ 150022/24 so..12 MJ 150022 and 12 MJ 150024...
just being sure.
First, I'd call and talk with Jon Soderberg to see if he has the originals.
Also, ask him about power supply caps while you have him on the phone. He supplies new ones and they will be expensive (they cost him lots as well) - just so you know and you don't feel like you're being ripped off.
http://www.vintageamprepair.net/
Let him know you're fixing it yourself because you want to learn.
Just see what he recommends, either the originals (if he has them) or which part numbers for replacements. Keep in mind that he runs a business repairing these things so he does need to make a profit. But, he knows his stuff, is honest, and fair - can't ask for more than that! Also, it's worth something to be able to pick up the phone and call him if you have questions.
If his price is right, buy the stuff from him. He's a good guy!
As far as figuring out which replacements will work, download the datasheets from the originals and then the MJ series that we've talked about. Compare the two and see what you find 😉
Also, ask him about power supply caps while you have him on the phone. He supplies new ones and they will be expensive (they cost him lots as well) - just so you know and you don't feel like you're being ripped off.
http://www.vintageamprepair.net/
Let him know you're fixing it yourself because you want to learn.
Just see what he recommends, either the originals (if he has them) or which part numbers for replacements. Keep in mind that he runs a business repairing these things so he does need to make a profit. But, he knows his stuff, is honest, and fair - can't ask for more than that! Also, it's worth something to be able to pick up the phone and call him if you have questions.
If his price is right, buy the stuff from him. He's a good guy!
As far as figuring out which replacements will work, download the datasheets from the originals and then the MJ series that we've talked about. Compare the two and see what you find 😉
Okay.. all my sources on MOTOROLA brand are $14.00 roughly.. or $8.00 used from vintage..
So... I want to test them and replace what is necessary.. am I capable? Do I just need to buy a tester?
So... I want to test them and replace what is necessary.. am I capable? Do I just need to buy a tester?
Sure you're capable...
Make sure your meter has good batteries in it. Hopefully it will have enough drive...
A true tester would be better but just use your meter like Grey advised in his post here:
http://www.diyaudio.com/forums/showthread.php?postid=1118116#post1118116
Also, regarding power supply caps, what did Jon say? You might also be interested in the thread here as they'd work for your application as well:
http://www.diyaudio.com/forums/showthread.php?postid=1121818#post1121818
Keep us posted as to what you find.
Make sure your meter has good batteries in it. Hopefully it will have enough drive...
A true tester would be better but just use your meter like Grey advised in his post here:
http://www.diyaudio.com/forums/showthread.php?postid=1118116#post1118116
Also, regarding power supply caps, what did Jon say? You might also be interested in the thread here as they'd work for your application as well:
http://www.diyaudio.com/forums/showthread.php?postid=1121818#post1121818
Keep us posted as to what you find.
His wife called me back and left a message.. I am going to start pulling the transistors tonight if I can get some solder wick somewhere..
I will call Jon again when I know how many transistors I need and ask about the caps.. thanks again!!!!!!!!
I will call Jon again when I know how many transistors I need and ask about the caps.. thanks again!!!!!!!!
Hi Terry,
I saw your post in one of the other theads. Great job on it!!!!
You can either use permanent black marker or hit the heatsinks with flat paint on top and that'd clean up the edges...
Where did you find the replacement window?
Again, beautiful job!
I saw your post in one of the other theads. Great job on it!!!!
You can either use permanent black marker or hit the heatsinks with flat paint on top and that'd clean up the edges...
Where did you find the replacement window?
Again, beautiful job!
THRESHOLD 400A
Thanks.
I built up some pretty good muscles refinishing the front plate.
Another member clued me in about the magic marker trick - the picture I posted was before I retouched the heatsinks.
I found the plexiglas window at a dealer in Texas who said
that was the last one they had and they were just about to throw it out!!!!
I know how the guy feels who is restoring the eBay 400A we are all learning so much about on this thread. I hope he gets the same satisfaction out of the results as I have!!!!
It's been pure joy to cross the Threshold and explore the Pass!
Terry Keith
Thanks.
I built up some pretty good muscles refinishing the front plate.
Another member clued me in about the magic marker trick - the picture I posted was before I retouched the heatsinks.
I found the plexiglas window at a dealer in Texas who said
that was the last one they had and they were just about to throw it out!!!!
I know how the guy feels who is restoring the eBay 400A we are all learning so much about on this thread. I hope he gets the same satisfaction out of the results as I have!!!!
It's been pure joy to cross the Threshold and explore the Pass!
Terry Keith
Attachments
Hi Terry, your project is old news.. I've read your thread a bunch of times.. 🙂 You did a great job.. I only wish I got mine as cheap as you got yours! Im on a fine line budget and have to make sure I dont make a mistake.. its not the money so much as the principle.. Just like to prove to myself I can do it without it costing more than its worth as some of told me will happen..
You did a great job.. did you use wet sand paper or something on the front? I missed the details of that part some where.... Mine really needs the exact same treatment as yours...
Like the band "The Tubes" song.. "She's a beauty!".
You did a great job.. did you use wet sand paper or something on the front? I missed the details of that part some where.... Mine really needs the exact same treatment as yours...
Like the band "The Tubes" song.. "She's a beauty!".
Might I suggest that your concept of worth needs adjusting?
Okay, so this project costs you X dollars...tell me how much you would spend taking a night class learning these same things. College classes? Private tutoring?
Harrumph!
Bargain.
Even if it costs you $50-100 more than the amp is "worth."
If your meter will directly test PN junctions (some Fluke meters will, for instance), then you're looking for something like .65V across the junction in one direction, infinite in the other direction. Otherwise, test as resistance.
If you choose to test Beta in your output devices, then you can get by with a meter, a simple power supply, and a resistor. Not too expensive or difficult to do.
By the way, I think you're doing the honorable thing and deserve a tip of the hat. As I said in earlier posts, it'd be a shame to kill off this particular amp. Courage and good luck.
Grey
Okay, so this project costs you X dollars...tell me how much you would spend taking a night class learning these same things. College classes? Private tutoring?
Harrumph!
Bargain.
Even if it costs you $50-100 more than the amp is "worth."
If your meter will directly test PN junctions (some Fluke meters will, for instance), then you're looking for something like .65V across the junction in one direction, infinite in the other direction. Otherwise, test as resistance.
If you choose to test Beta in your output devices, then you can get by with a meter, a simple power supply, and a resistor. Not too expensive or difficult to do.
By the way, I think you're doing the honorable thing and deserve a tip of the hat. As I said in earlier posts, it'd be a shame to kill off this particular amp. Courage and good luck.
Grey
Hi Terry,
You did do a beautiful job there. That's how a restoration is done! I'm sure the difference in price was easily eaten up in labour! 😉
Hi barchetta,
I to am glad you've decided to rebuild this classic. No more about your value system as that is what drives me up the wall.
I do wish you success with the help from all the assistance of members that have replied so far.
The master is watching (The one and only 😎 ) so you'd better do a good job! 😉 Kidding. If you do a good job you'll have this amp for many years to come.
-Chris
You did do a beautiful job there. That's how a restoration is done! I'm sure the difference in price was easily eaten up in labour! 😉
Hi barchetta,
I to am glad you've decided to rebuild this classic. No more about your value system as that is what drives me up the wall.
I do wish you success with the help from all the assistance of members that have replied so far.
The master is watching (The one and only 😎 ) so you'd better do a good job! 😉 Kidding. If you do a good job you'll have this amp for many years to come.
-Chris
barchetta said:
look at link I gave you in my previous post; there you have everything you need to know regarding testing transistors
Welp out of 12 transistors I found 0 good. Most were just open.
for $14.00 new, $8.00 used what would you buy? Transistors dont wear out like caps right? They either work or do not (except for the whole match thing which I doubt I will be able to do)..
for $14.00 new, $8.00 used what would you buy? Transistors dont wear out like caps right? They either work or do not (except for the whole match thing which I doubt I will be able to do)..
Are we talking about all original part numbers or the MJ series?
The ones from Jon will already be tested and good so nothing to worry about.
Since the other channel is mixed anyway, buy them from Jon and save yourself some $$$.
If you were replacing everything in both channels and matching them, then I would definitely buy new. But, as a low cost fix, I wouldn't worry about it and it will still be great!
You should pull one known good one from the other channel just to be sure that your meter has enough drive to test them properly. Since you wrote that "most" were just open, I'm a little bit suspicious.
On the other hand, it only takes one shorted one to send DC out to the speakers. Perhaps they didn't all cascade when they blew.
I still wish you a "real" tester.
Just my thoughts...
The ones from Jon will already be tested and good so nothing to worry about.
Since the other channel is mixed anyway, buy them from Jon and save yourself some $$$.
If you were replacing everything in both channels and matching them, then I would definitely buy new. But, as a low cost fix, I wouldn't worry about it and it will still be great!
You should pull one known good one from the other channel just to be sure that your meter has enough drive to test them properly. Since you wrote that "most" were just open, I'm a little bit suspicious.
On the other hand, it only takes one shorted one to send DC out to the speakers. Perhaps they didn't all cascade when they blew.
I still wish you a "real" tester.
Just my thoughts...