Radio shack should have that part...
Just check the voltage rating.
I think they stock 16v units but one of their assortments might have higher voltages in it.
Just check the voltage rating.
I think they stock 16v units but one of their assortments might have higher voltages in it.
I found a newer stereo I bought at a garage sale for $5.00 and scavenged it.. if it werent just the display I would not have done it. 🙂 Worked great.. 🙂 It took a puke anyway.. used to use it outside for the hot-tub 😉
I am going to tear down the other channel next.. then I will be done with this other than the bias tweek.. unless you guys have any other ideas on sound improvement.. (I will do the internal cables as well).. All the mods I know of are proprietary (secret)..
Thanks again for all your help guys! I am hoping this is a done deal now.. Should be ready to put into service by next weekend.. then I can rebuild my other 400a.. Should be about the same procedure. Its a newer unit but should be the same deal.. and I already bought the transistors so those are ready to go in. According to Jon fron Vintage this is the best thing you can do to make sure you do not have a catsrophic failure.. (and the caps of course).
Man these two are gonna be good for another 20 yrs!
Joe
I am going to tear down the other channel next.. then I will be done with this other than the bias tweek.. unless you guys have any other ideas on sound improvement.. (I will do the internal cables as well).. All the mods I know of are proprietary (secret)..
Thanks again for all your help guys! I am hoping this is a done deal now.. Should be ready to put into service by next weekend.. then I can rebuild my other 400a.. Should be about the same procedure. Its a newer unit but should be the same deal.. and I already bought the transistors so those are ready to go in. According to Jon fron Vintage this is the best thing you can do to make sure you do not have a catsrophic failure.. (and the caps of course).
Man these two are gonna be good for another 20 yrs!
Joe
barchetta said:
Anatech, you are amazing. As far as I recall you had answers to any problem people are posting, including mine with Hafler. Hats down to you. You really have to be good to recognize problem just based on description. We are all fortunate to have you on this forum.
Peace
AR2
Hi AR2,
Thanks for that. I like to help, and when you get burned you remember it. I've been burned a fair amount in the last 30 years. 😉 This is my way of returning the favour for every tech who has helped me along the way.
Anyone remember Jack Darr? He was my hero (even though I hate TV's on my bench 😉 )
-Chris
Thanks for that. I like to help, and when you get burned you remember it. I've been burned a fair amount in the last 30 years. 😉 This is my way of returning the favour for every tech who has helped me along the way.
Anyone remember Jack Darr? He was my hero (even though I hate TV's on my bench 😉 )
-Chris
Well I have bad news. I got all my parts in to rebuild the other channel.. and I went ahead and got ALL the resistors that were wire wound and replaced them.. so all lytics resistors and power trans.. put it back together then put it on the variac with one side connected.. slowly brought it up and measured 50mv DC.. then tried music.. played great.. brought the other side up slow as well.. measures 30mvDC.. connected music up.. played great.. I was very happy.. I had mounted the power switch upside down so after a few minutes of both channels playing I powered it down and removed the switch and replaced it correctly.. then I figured I didnt need the variac and I disconnected it and plugged the amp in directly.. power it up and no sound.. looked around and realized I had inadvertanly unplugged power to my CD player.. as soon as I plugged it in BUZZZZZZZ I unplugged it instantly and the buzz remained.. I flipped the power switch as fast as I could get to it (probably buzzed for about 5 seconds).. and I also noticed a puff of smoke near the resistor at the right channel ouput (the grounding resistor?) ..
So I unplugged the inputs from my preamp and brough it up slow.. 500mv DC at the outputs.. disconnect one channel at a time.. major DC even at small amounts of AC from the variac..
so then I measured DC output to each board.. I measure 60vDC at the positive wire with a ground on the chassis to my multimeter.. I flipped my multimeter to ac and I see 120v.. when I connect the ground of my multimeter to the negative cable off the caps to the left or right boards I get 240v AC...
What is going on? Is my rectifier fried?
**** that was a lot of work that just went up in smoke.
Depressing.
So I unplugged the inputs from my preamp and brough it up slow.. 500mv DC at the outputs.. disconnect one channel at a time.. major DC even at small amounts of AC from the variac..
so then I measured DC output to each board.. I measure 60vDC at the positive wire with a ground on the chassis to my multimeter.. I flipped my multimeter to ac and I see 120v.. when I connect the ground of my multimeter to the negative cable off the caps to the left or right boards I get 240v AC...
What is going on? Is my rectifier fried?
**** that was a lot of work that just went up in smoke.
Depressing.
Well, it's depressing but I suggest you get over it.
Look at how much personal progress you've made (even with
ignoring my ordinarily expensive advice).
Now that you're partially experienced, and after a good night's
sleep, it will be time to methodically go at it again. If you keep
at it, there's no particular limit.
BTW I have a nice signed archival document for you, but you
must send me your mailing address.
😎
Look at how much personal progress you've made (even with
ignoring my ordinarily expensive advice).
Now that you're partially experienced, and after a good night's
sleep, it will be time to methodically go at it again. If you keep
at it, there's no particular limit.
BTW I have a nice signed archival document for you, but you
must send me your mailing address.
😎
Nelson Pass said:Well, it's depressing but I suggest you get over it.
Look at how much personal progress you've made (even with
ignoring my ordinarily expensive advice).
Now that you're partially experienced, and after a good night's
sleep, it will be time to methodically go at it again. If you keep
at it, there's no particular limit.
BTW I have a nice signed archival document for you, but you
must send me your mailing address.
😎
I did email you my address, I will send it again.
I dont know what advice I ignored. Only thing I recall is you mentioning that the power transistors where slower than you'd recommend and to check for oscillations.. Not sure if this is what you meant or not.
EDIT: I just read every single response and still cant figure out what I ignored.. cept for checking for oscillations.. which I have no equipment to do.. I would assume I need an oscilloscope.. Your orginal post suggest bad ground at interconnect.. well the rca jacks are worn.. but I am not sure if this would cause the issue.. I can tell you my source has really badly worn RCA' jacks.. and I am using a very cheap interconnect.
I can't imagine replacing transistors at this point if I dont know what caused this. I'm seeing 100v ac across the caps with power disconnected.. I can't understand that.. I didnt think caps could generate AC.. or is this just my cheap multi-meter?
I have to think that either this is the wrong power transistors or something in the power supply. Its the only logical deduction I can think of.
Any advice would be much appreciated...
UPDATE:
I got to thinking about Mr. Pass's comments.. his original comment was the oscillations would cause the resistors at the outputs to burn.. so then I thought well.. what would cause this.. those little tan components must act like a circuit breaker... and ground out the postive output to the resistor.. so then I thought; well.. lemme bleed down the caps all the way and see if those "breakers" reset.. well; not sure if that is what happened but the amp is working again..
So my guess: ocillations caused the "breakers" to go closed and bleed down the outputs (I assume this is a safety circuit so you dont start a fire inside your speaker cabinet??)..
So, now I can go to sleep knowing I didnt fry everything..
These little tan components are no on the schematics.. can someone explain them to me? My pictures clearly show them if you dont know what I am speaking of..
So, now I am still not sure what to do.. maybe just a surge from the CD player caused this??
I got to thinking about Mr. Pass's comments.. his original comment was the oscillations would cause the resistors at the outputs to burn.. so then I thought well.. what would cause this.. those little tan components must act like a circuit breaker... and ground out the postive output to the resistor.. so then I thought; well.. lemme bleed down the caps all the way and see if those "breakers" reset.. well; not sure if that is what happened but the amp is working again..
So my guess: ocillations caused the "breakers" to go closed and bleed down the outputs (I assume this is a safety circuit so you dont start a fire inside your speaker cabinet??)..
So, now I can go to sleep knowing I didnt fry everything..
These little tan components are no on the schematics.. can someone explain them to me? My pictures clearly show them if you dont know what I am speaking of..
So, now I am still not sure what to do.. maybe just a surge from the CD player caused this??
Nelson Pass said:
Papa, children of today know all by themselves . . . hehe
There are few things you don't know . . . hehe
From what I read I suspect you had a temporarily bad ground or major ground loop.
Get yourself solid, clean and reliable connection between source and amp, amp and speakers.
A vast amount of AC across the caps would indicate a broken bridge rectifier. It's kind of strange though as you said the amp plays again.
You are the fearless kind as over here and with this type of amps the variac and light bulb stays in the circuit for hours, days sometimes.
🙂
/Hugo
Get yourself solid, clean and reliable connection between source and amp, amp and speakers.
A vast amount of AC across the caps would indicate a broken bridge rectifier. It's kind of strange though as you said the amp plays again.
You are the fearless kind as over here and with this type of amps the variac and light bulb stays in the circuit for hours, days sometimes.
🙂/Hugo
Netlist: thanks for the reply.. Maybe I am pushing it but if I had done as you suggest I am gussing this same scenerio would have occured.
Bobowanna: I see you predicted correctly and you were sent to Texas. If I am ignorning advice please tell me what it is.. Remember: I FIXED the right side and I was just upgrading the left.. So I felt it was pretty safe to go to music test.
I still dont know what this component is; I'll try and google it.
BTW.. I also renewed that cap on the bottom of the picture.
EDIT: Looks like its a pmt/2r cap.. I guess it is on the schematic but the resistor is shown first then the cap then to ground. Its listed as .1uf on the schematic.. should I replace these? Might they be faulty? BOTH resistors were burned when I received the broken unit (both outputs).
I am not sure how to test a cap.. okay I'll google that now 🙂
Bobowanna: I see you predicted correctly and you were sent to Texas. If I am ignorning advice please tell me what it is.. Remember: I FIXED the right side and I was just upgrading the left.. So I felt it was pretty safe to go to music test.
I still dont know what this component is; I'll try and google it.
An externally hosted image should be here but it was not working when we last tested it.
BTW.. I also renewed that cap on the bottom of the picture.
EDIT: Looks like its a pmt/2r cap.. I guess it is on the schematic but the resistor is shown first then the cap then to ground. Its listed as .1uf on the schematic.. should I replace these? Might they be faulty? BOTH resistors were burned when I received the broken unit (both outputs).
I am not sure how to test a cap.. okay I'll google that now 🙂
Upgraded the interconnects (stolen from my main system).. been playing for about 30 min.. dc output is now lower? 15mv left 32mv right. Not sure how this can happen.. caps "breaking in"? Is there such a thing? Or, is it just the bias changing as it warms up? I'm guessing the later...
Sounds pretty damn good.. I think I will measure and note bias and close it up.. Oh and I cleaned the rca inputs.. they were pretty dirty.. this unit was probably a used by a DJ.. rca's are worn and the unit was rack mounted at one point.
I feel as though I am talking to myself but I thought this might help someone in the future. Maybe this thread should be renamed 400a blog. LOL
J
Sounds pretty damn good.. I think I will measure and note bias and close it up.. Oh and I cleaned the rca inputs.. they were pretty dirty.. this unit was probably a used by a DJ.. rca's are worn and the unit was rack mounted at one point.
I feel as though I am talking to myself but I thought this might help someone in the future. Maybe this thread should be renamed 400a blog. LOL
J
Hi Joe,
The resistor - capacitor network you are showing is sometimes called a zobel network (at least that'a what I call it). If the resistor burns out it is a sure sign that your amplifier is oscillating for some reason. I would change both the resistor and the capacitor it's connected to.
With any luck it was only poor input connections. I am not familiar enough with this amp to tell you if there are other problems, but I do know some amplifiers react this way with poor input grounding.
Now you've learned. Always turn equipment off when making connections, and the amplifier gets turned on last and off first as a rule of thumb.
-Chris
The resistor - capacitor network you are showing is sometimes called a zobel network (at least that'a what I call it). If the resistor burns out it is a sure sign that your amplifier is oscillating for some reason. I would change both the resistor and the capacitor it's connected to.
With any luck it was only poor input connections. I am not familiar enough with this amp to tell you if there are other problems, but I do know some amplifiers react this way with poor input grounding.
Now you've learned. Always turn equipment off when making connections, and the amplifier gets turned on last and off first as a rule of thumb.
-Chris
Hi Joe,
Good morning!
Sorry to read about the bad news. Glad nothing was seriously damaged!
I think I will measure and note bias and close it up..
You're not done yet.
First, toss that cheap interconnect.
Next, as I suggested in a previous post, I'd replace the input jacks while you're at it. Again, I'd install the jacks I suggested as they're very high quality. Also, they just look cool...
You also need to measure and adjust the bias so both channels are matched.
As Nelson mentioned, get over it. Not being a jerk, just want you to stick with it. We've all been where you are more times than we would like and each time we learn more...
Remember all those comments folks were making at the beginning about fixing big amps? This is one of the "experience bumps" they were concerned about.
Anyway, as I recall, you said you LIKED smoke tests...
Again, glad most of the magic smoke stayed in - consider yourself lucky!!!
Best,
Good morning!
Sorry to read about the bad news. Glad nothing was seriously damaged!
I think I will measure and note bias and close it up..
You're not done yet.
First, toss that cheap interconnect.
Next, as I suggested in a previous post, I'd replace the input jacks while you're at it. Again, I'd install the jacks I suggested as they're very high quality. Also, they just look cool...
You also need to measure and adjust the bias so both channels are matched.
As Nelson mentioned, get over it. Not being a jerk, just want you to stick with it. We've all been where you are more times than we would like and each time we learn more...
Remember all those comments folks were making at the beginning about fixing big amps? This is one of the "experience bumps" they were concerned about.
Anyway, as I recall, you said you LIKED smoke tests...
Again, glad most of the magic smoke stayed in - consider yourself lucky!!!
Best,
Morning guys. Yes, i do need to order those rca's.. I keep gettig close and then something goes wrong with the order process.. I just need to call and order (they need an e-commerce for dummy's book).
Yes, I know that whats Nelson Pass was saying when he said get over it.. I took no offense.. but I still dont know what he meant when he said I was ignoring his advice.. can you guys explain?
Interconnects are tossed.. I cut them in half and it felt really good doing it.. Now I need to really hunker down and read that link about bias adjustment you sent me.. I'm still not reading the bias at the right location because I am seeing 22v.. probably wrong side of emitter resistor... but I am not sure.
I am a bit freightened to set it the way Mr. Pass recommends.. too hot to hold onto the heat sink after 10 seconds seems damn hot.. but maybe this will transform BOTH of my amps because neither even runs close. I will make very slow changes.
Anatech; yeah I will order.. my only issue is that I am not sure what the value is of the cap in my amp.. NONE of the components are the same as in the schematic.. this thing must have really gone thru a bunch of changes over the years!! And maybe this is one reason why.. if an idiot like me plugs in a source device it will fry.. maybe the interconnect.. but maybe not (I will not be re-running that little experiment).. and yeah .. I DIDN'T KNOW ABOUT THE SEQUENCE! But makes sense.. let the sources stablize before engaging warp drive.
Thanks again guys.. I'll report back when I get the bias adjusted. It played great for about 1 hour though.. but probably not hot enough as I mentioned......
EDIT:
http://www.trueaudio.com/st_zobel.htm
"Adding a Zobel to a woofer will allow the passive crossover to work more effectively. The impedance of the woofer will also be restored to the driver’s nominal impedance throughout the high frequency range. This technique allows the use of crossovers designed for resistive loads to operate as intended."
Got it! Nothing near what I thought it was!
Yes, I know that whats Nelson Pass was saying when he said get over it.. I took no offense.. but I still dont know what he meant when he said I was ignoring his advice.. can you guys explain?
Interconnects are tossed.. I cut them in half and it felt really good doing it.. Now I need to really hunker down and read that link about bias adjustment you sent me.. I'm still not reading the bias at the right location because I am seeing 22v.. probably wrong side of emitter resistor... but I am not sure.
I am a bit freightened to set it the way Mr. Pass recommends.. too hot to hold onto the heat sink after 10 seconds seems damn hot.. but maybe this will transform BOTH of my amps because neither even runs close. I will make very slow changes.
Anatech; yeah I will order.. my only issue is that I am not sure what the value is of the cap in my amp.. NONE of the components are the same as in the schematic.. this thing must have really gone thru a bunch of changes over the years!! And maybe this is one reason why.. if an idiot like me plugs in a source device it will fry.. maybe the interconnect.. but maybe not (I will not be re-running that little experiment).. and yeah .. I DIDN'T KNOW ABOUT THE SEQUENCE! But makes sense.. let the sources stablize before engaging warp drive.
Thanks again guys.. I'll report back when I get the bias adjusted. It played great for about 1 hour though.. but probably not hot enough as I mentioned......
EDIT:
http://www.trueaudio.com/st_zobel.htm
"Adding a Zobel to a woofer will allow the passive crossover to work more effectively. The impedance of the woofer will also be restored to the driver’s nominal impedance throughout the high frequency range. This technique allows the use of crossovers designed for resistive loads to operate as intended."
Got it! Nothing near what I thought it was!
Hi Joe,
Your link points to but one use for a zobel. It's also used to stabilize an amplifier by providing an HF load. Most amplifiers use them. Note that the values are not critical. Either use the values you do have, or follow the schematic. I would normally install what was there unless there is a service note to the contrary.
Nelson mentioned that he was sending you a manual. It can't be more than a few days away. Don't use your amp without the zobel though. You can't even set the bias current right now. So turn it off until you have the zobel fixed and you have the proper documentation.
Just one more thing to say. Often an individual amplifier may have component values differing from the published schematic. It doesn't mean that earlier ones were wrong. It also may mean that different output devices were used (or drivers, etc). Older techs are very used to seeing this.
-Chris
Your link points to but one use for a zobel. It's also used to stabilize an amplifier by providing an HF load. Most amplifiers use them. Note that the values are not critical. Either use the values you do have, or follow the schematic. I would normally install what was there unless there is a service note to the contrary.
Nelson mentioned that he was sending you a manual. It can't be more than a few days away. Don't use your amp without the zobel though. You can't even set the bias current right now. So turn it off until you have the zobel fixed and you have the proper documentation.
Just one more thing to say. Often an individual amplifier may have component values differing from the published schematic. It doesn't mean that earlier ones were wrong. It also may mean that different output devices were used (or drivers, etc). Older techs are very used to seeing this.
-Chris
anatech said:
I replaced the resistor.. although it was fine.. but yeah the caps might be bad..
Thanks for the heads up on the schematics.. I guess I was erroring on staying with the original design in case a component with a different value required another component with a different value.. if that makes sense at all.
Good afternoon. It's nice to see that you didn't take out the
output stage 🙂
My original intention was to walk you through the thing, but
I perceived that you wanted to proceed more quickly than my
response rate. I mean no reproach by this - it's your learning
experience.
At this point I suggest you do several things, the first being to
get some 1 and 2 amp fast blow fuses and put them in series
with the AC line.
Until you figure out why you have a full power oscillation, run
the amp on variac only at lower than usual AC voltage with the
lowest fuse value that works. Set the bias low on both channels.
Don't replace any more parts until you get a handle on the
problem.
Make up a pair of shorted male RCA connectors and put them
on the inputs so that the input has a grounded source but is
not otherwise attached to the outside world.
If they are opened (ohmmeter test) replace the resistors on the
output RC network with something comparable at about 5 ohms,
3 watts.
It is not probable that you had bad RCA connectors. Usually if
even one of these has a connection, it will ground for both
channels. First, I would look for a bad internal input ground or
ungrounded cable shield. Check all your internal wiring twice
and try to confirm all connections with an ohmmeter. I don't
need to tell you to do this with the power cord unplugged.
Make sure that your output wiring has no proximity to the input
wiring.
After you have done all this, turn the amp on at low AC voltage
with no source or load, and note the voltage on the cases of
all the output transistors, both channels.
😎
output stage 🙂
My original intention was to walk you through the thing, but
I perceived that you wanted to proceed more quickly than my
response rate. I mean no reproach by this - it's your learning
experience.
At this point I suggest you do several things, the first being to
get some 1 and 2 amp fast blow fuses and put them in series
with the AC line.
Until you figure out why you have a full power oscillation, run
the amp on variac only at lower than usual AC voltage with the
lowest fuse value that works. Set the bias low on both channels.
Don't replace any more parts until you get a handle on the
problem.
Make up a pair of shorted male RCA connectors and put them
on the inputs so that the input has a grounded source but is
not otherwise attached to the outside world.
If they are opened (ohmmeter test) replace the resistors on the
output RC network with something comparable at about 5 ohms,
3 watts.
It is not probable that you had bad RCA connectors. Usually if
even one of these has a connection, it will ground for both
channels. First, I would look for a bad internal input ground or
ungrounded cable shield. Check all your internal wiring twice
and try to confirm all connections with an ohmmeter. I don't
need to tell you to do this with the power cord unplugged.
Make sure that your output wiring has no proximity to the input
wiring.
After you have done all this, turn the amp on at low AC voltage
with no source or load, and note the voltage on the cases of
all the output transistors, both channels.
😎
Hi Nelson,
You know, it's been years since I've worked on one of these and I don't have the proper service manual either.
I'm all for stepping way back and letting you go through it with Joe. I'll learn myself at the same time. It is rare to have a product desiner assist with an older product.
-Chris 😉
You know, it's been years since I've worked on one of these and I don't have the proper service manual either.
I'm all for stepping way back and letting you go through it with Joe. I'll learn myself at the same time. It is rare to have a product desiner assist with an older product.
-Chris 😉
Just so there aren't any false expectations, I don't have a
service manual for it either, but it's a simple enough circuit.
😎
service manual for it either, but it's a simple enough circuit.
😎