I bought 3 Peavey CS-800 amps. All have issues. Strangly enough, they all do the same. I replaced the fuse, and plugged it into my DBT. The light glows bright, and dims down.
But when I connect a speaker to either channel, the bulb is bright as can be and stays that way.
The speaker is fine. They were all caked in nicotine dust, and are all clean. So its happy and stuff. I don't want to take it off the DBT, because I don't want to kill the amp.
I'm using a 100W lightbulb. This is the original PV-800. It is the same model as the one shown in this picture. (I got the pict off Google, its not my actual amp.
The traic boards are fine. Should I start checking the outputs for shorts?
-Nick
But when I connect a speaker to either channel, the bulb is bright as can be and stays that way.
The speaker is fine. They were all caked in nicotine dust, and are all clean. So its happy and stuff. I don't want to take it off the DBT, because I don't want to kill the amp.I'm using a 100W lightbulb. This is the original PV-800. It is the same model as the one shown in this picture. (I got the pict off Google, its not my actual amp.
An externally hosted image should be here but it was not working when we last tested it.
The traic boards are fine. Should I start checking the outputs for shorts?
-Nick
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Also, I removed the triac. I'm not using speakers of value on the amp anyways, and if something little shorted the triac, it could lead to costly amp repairs, instead of new speakers.
Can I remove some of the fancy wiring that I'll never use? Like the bridge mode switch and wiring (would I have to do something to the boards after) and wires that power the octal sockets for 70V transformers?
My main thing is I want to get these amps working. I'm going to sell one, and keep two. Can't sell one or use one if they are all goofed.
Lastly, the fuse is 15A. The fuse has a white casing (ceramic fuse I would assume) is this fuse a fast blo or slowblo? I assume slow blo, as I don't see a soft start circuit inside.
Can I remove some of the fancy wiring that I'll never use? Like the bridge mode switch and wiring (would I have to do something to the boards after) and wires that power the octal sockets for 70V transformers?
My main thing is I want to get these amps working. I'm going to sell one, and keep two. Can't sell one or use one if they are all goofed.
Lastly, the fuse is 15A. The fuse has a white casing (ceramic fuse I would assume) is this fuse a fast blo or slowblo? I assume slow blo, as I don't see a soft start circuit inside.
15 amp fuses in the 250 VAC rating are ceramic now instead of glass. Something about arc quenching. MDL are slow blow, AG3 are fast blow. Other brands than littlefuse, other codes. Look at the newark or mouser website for the codes and what they mean. For the alternative brand fuses you may have to look further.
What is a DBT? a light bulb box?
I test amps with 10 ohm 900 W resistors instead of speakers. (Two 5 ohm 450 W resistors mounted on a metal bracket to get them off the wood table). That way you can check for DC output without damaging speakers. Shorted output transistors cause DC output. After an amp starts coming back, I make audio checks with a 3900 uf back to back e-capacitor pair between the speaker and the amp output, in case O.T.'s continue to blow up (mine did until I built a 18V Ice leakage test jig). For this, outdated used capacitors are fine. They sound a little funny but not as bad as a destroyed amp does. I'm using 4 ohm 30 watt car speakers from Salvation Army resale, with a PTCR (resettable fuse)in series that could go to high resistance if the amps starts oscillating or puts out too much power.
These early CS800 models are going for $150 in unrestored condition in my market. I don't know if you could get enough for a unit with the overaged electrolytic capacitors and high hours fans replaced to be worth the parts cost of restoration. Transformer amps are out of fashion with pro bands (and my church music committee), when a switch supply amp weighs so much less and has up to date (reliable) capacitors. (the music committee says "we don't want any used music equipment" in their unsophisticated assessment).
If there is no DC output, I would disconnect the PCB's from the power board to see if the transformer rectifiers and electrolytic capacitors alone are okay. See if the +- rail voltage is per spec without load. Does that make the light bulb go out?
The CS800 b revision schematic is available on diyaudio.com. Have you downloaded it yet? If it is a later version, check eserviceinfo.com. You don't have to be a member there.
I've learned by burning PCB leads that the triac speaker fire protection circuit is the last thing to put back after attempting amp repair. Actually, I'm trying to replace the triac circuit with a power supply disconnect relay triggered by the diac if excessive DC output occurs. If you search CS800 here, you'll find other amp repairmen have done something similar to protect the speakers from blowups. The PV1.3k amp I'm trying to repair, the triac burned the leads off the PCB leading to it instead of protecting the speakers from DC.
What is a DBT? a light bulb box?
I test amps with 10 ohm 900 W resistors instead of speakers. (Two 5 ohm 450 W resistors mounted on a metal bracket to get them off the wood table). That way you can check for DC output without damaging speakers. Shorted output transistors cause DC output. After an amp starts coming back, I make audio checks with a 3900 uf back to back e-capacitor pair between the speaker and the amp output, in case O.T.'s continue to blow up (mine did until I built a 18V Ice leakage test jig). For this, outdated used capacitors are fine. They sound a little funny but not as bad as a destroyed amp does. I'm using 4 ohm 30 watt car speakers from Salvation Army resale, with a PTCR (resettable fuse)in series that could go to high resistance if the amps starts oscillating or puts out too much power.
These early CS800 models are going for $150 in unrestored condition in my market. I don't know if you could get enough for a unit with the overaged electrolytic capacitors and high hours fans replaced to be worth the parts cost of restoration. Transformer amps are out of fashion with pro bands (and my church music committee), when a switch supply amp weighs so much less and has up to date (reliable) capacitors. (the music committee says "we don't want any used music equipment" in their unsophisticated assessment).
If there is no DC output, I would disconnect the PCB's from the power board to see if the transformer rectifiers and electrolytic capacitors alone are okay. See if the +- rail voltage is per spec without load. Does that make the light bulb go out?
The CS800 b revision schematic is available on diyaudio.com. Have you downloaded it yet? If it is a later version, check eserviceinfo.com. You don't have to be a member there.
I've learned by burning PCB leads that the triac speaker fire protection circuit is the last thing to put back after attempting amp repair. Actually, I'm trying to replace the triac circuit with a power supply disconnect relay triggered by the diac if excessive DC output occurs. If you search CS800 here, you'll find other amp repairmen have done something similar to protect the speakers from blowups. The PV1.3k amp I'm trying to repair, the triac burned the leads off the PCB leading to it instead of protecting the speakers from DC.
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These amps are 200W PCh @ 8ohms and yeah at best they are worth $150each. big old ancient tanks. barely worth fixing yourself! and definitely not worth taking to any shop! in fact most repair shops have a few of these laying around holding doors open and propping up a bench in a corner someplace! the good is that they are easy to fix and you can just about throw any transistor in them and they will work...but yuck. what an old old crappy amp!
The power transformers, cases, and heat sinks of early CS800 amps are high class. The circuits are reliable unless run into shorts, but don't sound great until the CS800x CS800s revisions. In diyaudio, the transformers, heat sinks, and cases are what costs a lot. So think of what future good sounding amps you might like to build with revised driver boards. The TO3 output transistors are not the limitation on sound quality, the driver boards are.
But of course if you make it sound better (and non-standard) nobody will pay anything for it. I'm listening to 18-50 year old equipment at my house, playing music on 40-45 year old organs, and sit passively at church while the music committee demonstrates their new import wonders.
But of course if you make it sound better (and non-standard) nobody will pay anything for it. I'm listening to 18-50 year old equipment at my house, playing music on 40-45 year old organs, and sit passively at church while the music committee demonstrates their new import wonders.
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Here is the link to the schematic.
http://dl.dropbox.com/u/8335881/CS800.pdf
I know these aren't fancy amps, but I want to keep one for parties, and as a "beater" I know these are PA amps, and being able to be loud is the goal, not sound amazing.
The stocker on the bottom says
Model CS-800 Power Pak
Serial Number 0A-611206
On the other amp, it says the something but serial number
4A-01941016
And the 3rd one doesn't have a sticker, but is identical to the 0A-611206 amp. The 4A amp has the newer boards with the mono switch soldered to the board that also has the speaker posts soldered to it. (It has the TRIAC-A BD and TRIAC-B BD boards)
As for building a new amp, I can't I don't have money for that. I'm working on a Hafler XL-280 building a Musical Concepts PA-4 amp out of it, so thats that. These Peavey amps. I just want to keep stock and get them working.
And Zero Cool. Why are these amps so crappy? Sure they don't have the fidelity of a home amp, but they are for tasks that require LOUD music and stuff.
http://dl.dropbox.com/u/8335881/CS800.pdf
I know these aren't fancy amps, but I want to keep one for parties, and as a "beater" I know these are PA amps, and being able to be loud is the goal, not sound amazing.
The stocker on the bottom says
Model CS-800 Power Pak
Serial Number 0A-611206
On the other amp, it says the something but serial number
4A-01941016
And the 3rd one doesn't have a sticker, but is identical to the 0A-611206 amp. The 4A amp has the newer boards with the mono switch soldered to the board that also has the speaker posts soldered to it. (It has the TRIAC-A BD and TRIAC-B BD boards)
As for building a new amp, I can't I don't have money for that. I'm working on a Hafler XL-280 building a Musical Concepts PA-4 amp out of it, so thats that. These Peavey amps. I just want to keep stock and get them working.
And Zero Cool. Why are these amps so crappy? Sure they don't have the fidelity of a home amp, but they are for tasks that require LOUD music and stuff.
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I played in a 128 member high school band, so I like things sometimes both loud and accurate. Peavey CS800 early was okay loud, but not okay soft at all. Maybe the band wants to play Angie or Michelle for a slow dance.
When I say new driver board, I am thinking of a piece of lumberyard lexan drilled, with a half dozen $.09 transistors, a couple of $1.20 TO220 driver transistors, and some resistors and capacitors. The only thing that keeps me from doing that to replace the driver board in this PV1.3k is the connector to the output transistor board is something weird I can't match up. Even better, Nat Semi makes a LM4702 driver IC that connects right to the output driver (you have to buy the A grade part to get to 81 V rail voltage, the datasheet says). $7 at Newark, in stock.
Do you have DC on the output? Bad OT's. Is your rail power supply blowing fuses without the load (boards) connected? If so,leaky capacitors are likely,shorted rectifier is remotely possible,shorted turn transformer is an extremely remote possibility. Those 10 ohm 900 w resistors I have are also useful for testing the DC supply without the complicated boards as load.
When I say new driver board, I am thinking of a piece of lumberyard lexan drilled, with a half dozen $.09 transistors, a couple of $1.20 TO220 driver transistors, and some resistors and capacitors. The only thing that keeps me from doing that to replace the driver board in this PV1.3k is the connector to the output transistor board is something weird I can't match up. Even better, Nat Semi makes a LM4702 driver IC that connects right to the output driver (you have to buy the A grade part to get to 81 V rail voltage, the datasheet says). $7 at Newark, in stock.
Do you have DC on the output? Bad OT's. Is your rail power supply blowing fuses without the load (boards) connected? If so,leaky capacitors are likely,shorted rectifier is remotely possible,shorted turn transformer is an extremely remote possibility. Those 10 ohm 900 w resistors I have are also useful for testing the DC supply without the complicated boards as load.
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Well one channel works. The other does brightens the bulb up. Uploading a video to YouTube now. Lets call this amp 1. Now amp 2 does the same thing, but in both channels.. As for amp 3... lets forget that for now. Both amp 1 and 2 measure fine for the rails. So the power supply is happy. DC offset in BOTH amps for both channels falls to about 2mV, so DC offset is happy.
Before you connect any speaker or load to any output, turn on the amp and measure to see if there is DC voltage between the speaker output binding posts. We also want to measure with power off for a short across the output. That would be from a shorted triac. You may have done these things already.
If your amp runs cool without a load but lights it up with a load, then the load is working for SOMETHING. That something is almost always DC on the output. Other possibility is high level oscillations, but I can't say as I have seen that in my 26 years as authorized PV repair station.
PLEASE don;t start tearing out "fancy" wiring. All that stuff does nothing to get in the way of good operation, and as soon as you do something like that it adds so many MORE opporunities for something to go wrong. ALWAYS fix the amp before even considering modifications to it. Imagine you are having heart bypass operations. You wouldn;t say to the doctor, "Oh as long as you are operating, might as well do a facelift too."
Transistors have more than one failure mode, so no they don;t always blow fuses. A single shorted transistor at the output can put DC on the output, but that won;t necessarily blow fuses until you add a load.
The triac is protection. If the amp goes to DC, the triac shorts across it, and is supposed to blow the amp fuse. That usually kills the triac, but it prevents your speakers from CATCHING FIRE. They may be cheap speakers, but we don;t want them burning down your house. Also, little things don't blow the triacs, big things do, and those things are things that already mean the amp needs service.
You can use a glass fuse. Look on the rear panel by the fuse holder. If it says 15A Slow, then it is a slow blow. If it doesn't specifically say slow blow, then assume a plain old normal fast blow. These amps use a common fast fuse.
Crappy? No sir, these are incredibly sturdy, well built and reliable amps. Are ther modern amps with loads more performance? Sure. But you can fix them in a heartbeat when something breaks and they motor on another decade. They are the DC3 of the amplifier world. And there is no shortage of WW2 era DC3s still flying the world skies. DO I want ten of them in a rack, no of course not. I;d rather have those 7 pound 1600 watt things. I'd also like Anne Hathaway calling me for a date. Wants are not always what we get.
You have the two power modules in each amp, one per channel, and you can disconnect either or both simply by pulling the four wire molex connector from the output transistor board. This allows single channel operation to see what works. Once you have identified the bad and good channels, you can go further by swapping driver cards. You may find that in an amp with one bad channel, that both driver cards work in one channel and neither works in the other. That means the problem is on the power module itself and not the driver card. Or you may find that one of the cards make either channel work ok, but the remaining card doesnl;t work on either power module. All that at least isolates the problem to a module or a driver. And of course you could have a bad module AND a bad driver card.
You have three amps, The old style CS800 came in three types, the A, B, and C series. The earlier A and B had a driver card with one IC on it, and the volume control sat on a small board with nothing but two little transistors on it. The later C series CS800 had two ICs on the driver card, and the volume control board was larger, with two ICs and the volume control itself had the pull switch.
We may have schematics here, but for any you still need, customer service at Peavey will send you any you request. Your schematic is the C version. The differences I described should tell you which versions you have. Your serial numbers indicate amps from 1980 and 1984, so I suspect they are all C series.
If your amp runs cool without a load but lights it up with a load, then the load is working for SOMETHING. That something is almost always DC on the output. Other possibility is high level oscillations, but I can't say as I have seen that in my 26 years as authorized PV repair station.
PLEASE don;t start tearing out "fancy" wiring. All that stuff does nothing to get in the way of good operation, and as soon as you do something like that it adds so many MORE opporunities for something to go wrong. ALWAYS fix the amp before even considering modifications to it. Imagine you are having heart bypass operations. You wouldn;t say to the doctor, "Oh as long as you are operating, might as well do a facelift too."
Transistors have more than one failure mode, so no they don;t always blow fuses. A single shorted transistor at the output can put DC on the output, but that won;t necessarily blow fuses until you add a load.
The triac is protection. If the amp goes to DC, the triac shorts across it, and is supposed to blow the amp fuse. That usually kills the triac, but it prevents your speakers from CATCHING FIRE. They may be cheap speakers, but we don;t want them burning down your house. Also, little things don't blow the triacs, big things do, and those things are things that already mean the amp needs service.
You can use a glass fuse. Look on the rear panel by the fuse holder. If it says 15A Slow, then it is a slow blow. If it doesn't specifically say slow blow, then assume a plain old normal fast blow. These amps use a common fast fuse.
Crappy? No sir, these are incredibly sturdy, well built and reliable amps. Are ther modern amps with loads more performance? Sure. But you can fix them in a heartbeat when something breaks and they motor on another decade. They are the DC3 of the amplifier world. And there is no shortage of WW2 era DC3s still flying the world skies. DO I want ten of them in a rack, no of course not. I;d rather have those 7 pound 1600 watt things. I'd also like Anne Hathaway calling me for a date. Wants are not always what we get.
You have the two power modules in each amp, one per channel, and you can disconnect either or both simply by pulling the four wire molex connector from the output transistor board. This allows single channel operation to see what works. Once you have identified the bad and good channels, you can go further by swapping driver cards. You may find that in an amp with one bad channel, that both driver cards work in one channel and neither works in the other. That means the problem is on the power module itself and not the driver card. Or you may find that one of the cards make either channel work ok, but the remaining card doesnl;t work on either power module. All that at least isolates the problem to a module or a driver. And of course you could have a bad module AND a bad driver card.
You have three amps, The old style CS800 came in three types, the A, B, and C series. The earlier A and B had a driver card with one IC on it, and the volume control sat on a small board with nothing but two little transistors on it. The later C series CS800 had two ICs on the driver card, and the volume control board was larger, with two ICs and the volume control itself had the pull switch.
We may have schematics here, but for any you still need, customer service at Peavey will send you any you request. Your schematic is the C version. The differences I described should tell you which versions you have. Your serial numbers indicate amps from 1980 and 1984, so I suspect they are all C series.
Enzo! Thanks for chiming in. Here is a few questions. On amp 2, I plug it in with out anything connected, its fine. If I plug a speaker in, and turn it on, the bulb is bright, ad doesn't dim. But here is the odd part. If I disconnect the speaker when the amp is on and bulb is bright, the bulb dims down, and all is well. The strange thing, is while the amp is on, I can reconnect the speaker, and the bulb doesn't go full brightness.... and music plays through like it should. 
This happens for both channels.
Amp 2 actually came to me in working order. The only thing I goofed with is the triac output boards, I desoldered, and tossed the components crossed in red. But aren't those components simply just to protect the speakers? The amp should still work with out them.. right?
All three amps have 2 ICs on the driver card.
http://www.youtube.com/watch?v=1CH0VT2heAg
This happens for both channels.Amp 2 actually came to me in working order. The only thing I goofed with is the triac output boards, I desoldered, and tossed the components crossed in red. But aren't those components simply just to protect the speakers? The amp should still work with out them.. right?
All three amps have 2 ICs on the driver card.
http://www.youtube.com/watch?v=1CH0VT2heAg
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Yes, those traic and related parts are only protection, the amp will operate fine without them. You can likewise remove the seat belts and airbags from your car. It will still drive fine. I don't recommend it, but indeed the amp will amplify just fine without them. To kill it, all you really needed to remove was the triac itself. Those other parts won't get in the way. Or wouldn't have.
I won't hesitate to disconnect them during troubleshooting if I have any reason to think they will interfere, but i always have them working and in place when I am finished.
They protect your speakers, but not so much from being blown, but from catching fire. I wasn;t joking. They also intentionally short the output to blow the fuse. If they blow the fuse, it turns the amp off so no further damage can occur. This is called crowbar circuit.
Light bulb limiters are great, they save amps from further damage much of the time. However, they are not intended for amp operation. When the bulb is in, the voltages in the amp will be reduced. The amp can be a lot less stable that way, so it will usually work, but may not work right.
SO while they are great, we cannot trust the operation of an amp when on them. Especially into a load.
You need to find out what the amp is doing. You say you can make it work by turning it on without a load, THEN load it once on. But load it first then turn it on and we get bulb. OK, when you have brite bulb, what is on the output? Has it gone to DC?
If you can consistently fire it up with no load and the bulb is dim, then plug it into the wall directly, or use the other amp that already works, and measure the power rails - about 80v. Now on the amp that has this funny symptom, get it running by your method, then measure what those rails are now? I bet they are no longer 80v.
My working theory is that your amp is unstable under load on the bulb. The starting surge throws it into confusion. Your softer start up procedure gets it past that. But I bet if pushed it would still choke. Once we know the thing is not blown up, lose the bulb.. The bulb is there to prevent a blown amp from damaging itself further or charcoaling its parts. Once past that, I lose the bulb. Fire it up on direct mains and see what happens unloaded. You can use a dummy load instead of speakers then.
I won't hesitate to disconnect them during troubleshooting if I have any reason to think they will interfere, but i always have them working and in place when I am finished.
They protect your speakers, but not so much from being blown, but from catching fire. I wasn;t joking. They also intentionally short the output to blow the fuse. If they blow the fuse, it turns the amp off so no further damage can occur. This is called crowbar circuit.
Light bulb limiters are great, they save amps from further damage much of the time. However, they are not intended for amp operation. When the bulb is in, the voltages in the amp will be reduced. The amp can be a lot less stable that way, so it will usually work, but may not work right.
SO while they are great, we cannot trust the operation of an amp when on them. Especially into a load.
You need to find out what the amp is doing. You say you can make it work by turning it on without a load, THEN load it once on. But load it first then turn it on and we get bulb. OK, when you have brite bulb, what is on the output? Has it gone to DC?
If you can consistently fire it up with no load and the bulb is dim, then plug it into the wall directly, or use the other amp that already works, and measure the power rails - about 80v. Now on the amp that has this funny symptom, get it running by your method, then measure what those rails are now? I bet they are no longer 80v.
My working theory is that your amp is unstable under load on the bulb. The starting surge throws it into confusion. Your softer start up procedure gets it past that. But I bet if pushed it would still choke. Once we know the thing is not blown up, lose the bulb.. The bulb is there to prevent a blown amp from damaging itself further or charcoaling its parts. Once past that, I lose the bulb. Fire it up on direct mains and see what happens unloaded. You can use a dummy load instead of speakers then.
Hi Enzo! This video shows amp 2, and the "issue"
Peavey CS 800 amp 2 - YouTube
Do you think it would be different on mains power? I just don't want to hurt anything.
Peavey CS 800 amp 2 - YouTube
Do you think it would be different on mains power? I just don't want to hurt anything.
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Oh how I don't like watching yoou tubes, nothing personal sir. In fact I am one a new computer, on the old one I didn;t have sound connected precisely so I wouldn;t get roped into spending a lot of time on you tubes, cute songs, and other things people sent me. But i did watch yourws.
I already understood your description.
First a tangent, I think you are a bit confused about DC offsets and the triacs. Or I have been unclear, maybe it is more that. When I talk about DC offset on your output, I am worried about 40 volts or 80 volts, not a volt or two. Your Hafler and many others have an output offset trim, but it is good for a very small range of adjustment, It is there to correct for small skew on the thing, or to compensate for diffy pairs not quite in agreement. That ain't this. You Hafler will not trim out 40v. Your little triac is not there to burn up the amp over a volt or two, it is there to crowbar the output when dire things occur. It won;t be the cause of dead outputs, it will be the result of dead outputs. This amp is real stable as it sits, but if something fails in the amp, hopefully the triac will take out the fuse before anything can heat up and turn your board - or speakers - to charcoal. Transistors can short at the speed of light, no fuse is fast enough for that. But if something turns on those ooutp0uts into a dead short, they will conduct enough current to blow the fuse faster than they can heat up to failure point.
All your amps act the same? Did you happen to plug any into the wall to see how they react?
They come on with no load acting as you expect. On the bulb. Check for DC. YOu find no DC on the output. The thing to do then is plug it into the wall. No load, just the amp into the wall. Power up. Does it do that without blowing a fuse and without putting DC on the output? That is what we want to see.
You power up with a load, it goes nuts. power up without a load it is OK, and you can then add a load and it lets you. That is with the bulb. We already know that once it starts up OK, we can add a load, right? SO plug into the wall. If it powers up without a load that way, then we ought to expect it to be ok with adding a load then. We could be wrong, but I'd wager not.
I think I mentioned takling voltage readings inside. Did you do that? With the bulb, take the lid off, your output transistors are exposed. One row of them ought to have V+ on the cases. Power up, what voltage is on there? How close it it to the 80v the system wants? You are asking the amp to function properly while starving for volts. You mention the fan waiting to start up? What if that 120v fan is trying to start on 90 volts?
The bulb is a powerful tool, but it has its limits.
You mention the amp came in working, and all you did was remove the triac stuff, and now it does this. I bet my lunch money you didn't do the bulb test before you took the triac stuff out. DO I win that bet?
I could be way off base, but the bottom line is that we need to know what the amp is doing, ie what voltages are present and where. Looking at a bright bulb only tells us the amp has gone screwy, but not WHY.
You have heard amps go WHUMP when you power them up. That is a moment of instability as the power supplies charge up. If you bring one up slow on a variac, you can stretch that WHUMP out into a loud Buuzzzzzmmmmmmppp. IN fact often as not you can stop the variac and leave it mid thump. Not so good for amp or speaker, but you can do it. You bulb limits inrush and in effect slows down the WHUMP. I think your problem is it can;t get past mid-whump by itself on the bulb.
I already understood your description.
First a tangent, I think you are a bit confused about DC offsets and the triacs. Or I have been unclear, maybe it is more that. When I talk about DC offset on your output, I am worried about 40 volts or 80 volts, not a volt or two. Your Hafler and many others have an output offset trim, but it is good for a very small range of adjustment, It is there to correct for small skew on the thing, or to compensate for diffy pairs not quite in agreement. That ain't this. You Hafler will not trim out 40v. Your little triac is not there to burn up the amp over a volt or two, it is there to crowbar the output when dire things occur. It won;t be the cause of dead outputs, it will be the result of dead outputs. This amp is real stable as it sits, but if something fails in the amp, hopefully the triac will take out the fuse before anything can heat up and turn your board - or speakers - to charcoal. Transistors can short at the speed of light, no fuse is fast enough for that. But if something turns on those ooutp0uts into a dead short, they will conduct enough current to blow the fuse faster than they can heat up to failure point.
All your amps act the same? Did you happen to plug any into the wall to see how they react?
They come on with no load acting as you expect. On the bulb. Check for DC. YOu find no DC on the output. The thing to do then is plug it into the wall. No load, just the amp into the wall. Power up. Does it do that without blowing a fuse and without putting DC on the output? That is what we want to see.
You power up with a load, it goes nuts. power up without a load it is OK, and you can then add a load and it lets you. That is with the bulb. We already know that once it starts up OK, we can add a load, right? SO plug into the wall. If it powers up without a load that way, then we ought to expect it to be ok with adding a load then. We could be wrong, but I'd wager not.
I think I mentioned takling voltage readings inside. Did you do that? With the bulb, take the lid off, your output transistors are exposed. One row of them ought to have V+ on the cases. Power up, what voltage is on there? How close it it to the 80v the system wants? You are asking the amp to function properly while starving for volts. You mention the fan waiting to start up? What if that 120v fan is trying to start on 90 volts?
The bulb is a powerful tool, but it has its limits.
You mention the amp came in working, and all you did was remove the triac stuff, and now it does this. I bet my lunch money you didn't do the bulb test before you took the triac stuff out. DO I win that bet?
I could be way off base, but the bottom line is that we need to know what the amp is doing, ie what voltages are present and where. Looking at a bright bulb only tells us the amp has gone screwy, but not WHY.
You have heard amps go WHUMP when you power them up. That is a moment of instability as the power supplies charge up. If you bring one up slow on a variac, you can stretch that WHUMP out into a loud Buuzzzzzmmmmmmppp. IN fact often as not you can stop the variac and leave it mid thump. Not so good for amp or speaker, but you can do it. You bulb limits inrush and in effect slows down the WHUMP. I think your problem is it can;t get past mid-whump by itself on the bulb.
A couple other things: Have you measured the AC the amp is seeing when on the bulb? At both dim and bright modes? I am maaking up some numbers now to illustrate. Let us say when the bulb is dim, it eats 20 volts. That means the amp sees 100v if it doesn't ask for too much current. The amp can mostly run on 100v. Now what if we fire it up and the bulb brites on us? Well I am going to guess that the bulb when bright has maybe 80-90 volts across it. That leaves 30-40 volts for the amp. You were concerned the bulb, once it started out bright didn't seem to go back to dim on its own. Well, an amp trying to run on 30-40 volts has no way to drag itself back to proper operating conditions. SO it doesn;t.
You might find it informative to add an AC current meter in series with your mains. The bulb lights bright? OK, but how much current is being drawn to do that? A 120v 100 watt lamp draws 100/120 = 0.83 amps. Less than an amp. That means the amp is also drawing less than one amp. (Oh that was clumsy. I mean the amplifier is drawing less than one ampere. Sorry) Of course it is doing that at only the 30-40 volts, but still, it is a long way from the 15A mains fuse in the holder.
I think it is always important to put information in context.
You might find it informative to add an AC current meter in series with your mains. The bulb lights bright? OK, but how much current is being drawn to do that? A 120v 100 watt lamp draws 100/120 = 0.83 amps. Less than an amp. That means the amp is also drawing less than one amp. (Oh that was clumsy. I mean the amplifier is drawing less than one ampere. Sorry) Of course it is doing that at only the 30-40 volts, but still, it is a long way from the 15A mains fuse in the holder.
I think it is always important to put information in context.
Look like amp 2 is working and fine
Peavey CS-800 Amp 2 - YouTube
On a 100W light bulb, the rails are +60V and -60V That is low obviously, but when connected to the wall, I assume its regular +80V and -80V, although I didn't measure to confirm. The video shows the amp working, and such. Would I need to use a relay and stuff to prevent turn on and turn off thumps? My Hafler doesn't have those issues (it did before I rebuilt it) and I didn't need a relay. Enzo, does the triac board need to be presented with to short? Does it have to be DC to short, or could high spikes of AC kill it too?
Peavey CS-800 Amp 2 - YouTube
On a 100W light bulb, the rails are +60V and -60V That is low obviously, but when connected to the wall, I assume its regular +80V and -80V, although I didn't measure to confirm. The video shows the amp working, and such. Would I need to use a relay and stuff to prevent turn on and turn off thumps? My Hafler doesn't have those issues (it did before I rebuilt it) and I didn't need a relay. Enzo, does the triac board need to be presented with to short? Does it have to be DC to short, or could high spikes of AC kill it too?
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I don't worry about turn on thumps myself. You can engineer something if you have to get rid of them. I don't recall CS800 having a thump problem, but individual units might.
As was said, the triacs are like seatbelts on a car, they don't HAVE to be present for the amp to work. If a momentary spike trips the triac, it shunts the output until that signal crosses zero. Unless you disable it, this amp has the Peavey very effective DDT circuit that liits peaks to prevent clipping but stays out of the way otherwise. A transient peak won't kill the triac. Trying to be a dead short across an 80v rail will.
Like anything else, these amps can fail, but once runnint, they are tough and reliable just stock. I don't see any advantage removing stuff from them. Just my opinion.
As was said, the triacs are like seatbelts on a car, they don't HAVE to be present for the amp to work. If a momentary spike trips the triac, it shunts the output until that signal crosses zero. Unless you disable it, this amp has the Peavey very effective DDT circuit that liits peaks to prevent clipping but stays out of the way otherwise. A transient peak won't kill the triac. Trying to be a dead short across an 80v rail will.
Like anything else, these amps can fail, but once runnint, they are tough and reliable just stock. I don't see any advantage removing stuff from them. Just my opinion.
Enzo.. A few questions. What are modern replacements for the two ICs n the driver board, and what do they do? They look like they might be op amps. I know this is a stupid question, but what exactly is an op amp?
Also, what replacement output transistors should be used? I assume Its going to be an ON semi MJ something. I gather than these amps work with lots of transistors, but I want to know what the factory would use. Of the 3 amps, one has RCA branded outputs (this is amp 2.. the one that is working great) Amp 1 uses Motorola branded outputs, and amp 3 just has Peavey house numbers (no brand)
Even if their is a spec by spec replacement, I assume going up in the current rating would only make the outputs a bit more durable... right?
Now, is the amp designed to handle a short across the speaker terminals, and only blow a fuse, not the output transistors?
Another guy said it would be stupid if the triac when shorted would result in damaging the output transistors.. (Although the triac would only short of the output transistors were malfunctioning, or the amp had a major failure.)
My view on it is this. If a triac shorts, and the outputs are all working and happy, then they should withstand a short, and the fuse will blow, but the outputs being able to simply handle the dead short.
Lastly, the two transistors on the heatsink that aren't outputs- they appear to be drivers. Whats the modern replacement for them? Again, I assume its an ON Semi MJ something. If I ever need to replace these transistors, I would use ON Semi for them.
Thanks!
P.S.
I'll start troubleshooting amp 1 tomorrow.
Also, what replacement output transistors should be used? I assume Its going to be an ON semi MJ something. I gather than these amps work with lots of transistors, but I want to know what the factory would use. Of the 3 amps, one has RCA branded outputs (this is amp 2.. the one that is working great) Amp 1 uses Motorola branded outputs, and amp 3 just has Peavey house numbers (no brand)
Even if their is a spec by spec replacement, I assume going up in the current rating would only make the outputs a bit more durable... right?
Now, is the amp designed to handle a short across the speaker terminals, and only blow a fuse, not the output transistors?
Another guy said it would be stupid if the triac when shorted would result in damaging the output transistors.. (Although the triac would only short of the output transistors were malfunctioning, or the amp had a major failure.)
My view on it is this. If a triac shorts, and the outputs are all working and happy, then they should withstand a short, and the fuse will blow, but the outputs being able to simply handle the dead short.
Lastly, the two transistors on the heatsink that aren't outputs- they appear to be drivers. Whats the modern replacement for them? Again, I assume its an ON Semi MJ something. If I ever need to replace these transistors, I would use ON Semi for them.
Thanks!
P.S.
I'll start troubleshooting amp 1 tomorrow.