Hey Guys,
Bought a pair of Audio Research M100s and there are some issues with one of them. I sent it back and when it returned it still isn't right. The little bit that I have listened to them I have loved the sound and I hate to return them although that is an option. Any input would be greatly appreciated. I am not an electrical engineer. I am a bovine herder and manage a family ranch. If you can help you have an open invitation to visit. We'll kill a cow have a barbecue and sip tequilla until the cows come home. I do have a good meter and know how to use it.
The problem I believe is in the power supply. It uses three tubes as "Regulators". One of these is a 6550 and it is the "Screen regulator" for the output tubes. Before I sent it back it was getting way too hot to the point the plates in the tube were turning red. I know it is not my imagination. When it first happened I pulled one of the 6550s [Winged C] from the other Amp and substituted it for this regulator tube [Sovtek] and yes it helped but only for a short while. While the amp was at the shop I sent some tubes to be checked and sent this 6550 as well. The test results came back and it was extremely gassy indicative of a tube running too hot. I believe the output tubes were running somewhat hot as well. It got to the point that the regulator tubes brightness was oscillating as well as the volume. In my conversation with the salesman I told him all of this and as well that the output tubes would not bias which they would not. I think he told the tech that it had issues and wouldn't bias. Now I have it back and it has KT88s as output tubes and the regulator and yes it will bias right now but volume compared to the other amp is greatly diminished and that output tube is still getting hot as a firecracker. I feel if I continue to use it that it will get to the point it will not bias and ruin these KT88s as well. I am getting so paranoid about it that I would swear that all the tubes seem a little too bright There is a schematic of the amp at this site ARCDB - M-100 . As I said any input would be greatly appreciated.
Thanks
Tom Wild
Bought a pair of Audio Research M100s and there are some issues with one of them. I sent it back and when it returned it still isn't right. The little bit that I have listened to them I have loved the sound and I hate to return them although that is an option. Any input would be greatly appreciated. I am not an electrical engineer. I am a bovine herder and manage a family ranch. If you can help you have an open invitation to visit. We'll kill a cow have a barbecue and sip tequilla until the cows come home. I do have a good meter and know how to use it.
The problem I believe is in the power supply. It uses three tubes as "Regulators". One of these is a 6550 and it is the "Screen regulator" for the output tubes. Before I sent it back it was getting way too hot to the point the plates in the tube were turning red. I know it is not my imagination. When it first happened I pulled one of the 6550s [Winged C] from the other Amp and substituted it for this regulator tube [Sovtek] and yes it helped but only for a short while. While the amp was at the shop I sent some tubes to be checked and sent this 6550 as well. The test results came back and it was extremely gassy indicative of a tube running too hot. I believe the output tubes were running somewhat hot as well. It got to the point that the regulator tubes brightness was oscillating as well as the volume. In my conversation with the salesman I told him all of this and as well that the output tubes would not bias which they would not. I think he told the tech that it had issues and wouldn't bias. Now I have it back and it has KT88s as output tubes and the regulator and yes it will bias right now but volume compared to the other amp is greatly diminished and that output tube is still getting hot as a firecracker. I feel if I continue to use it that it will get to the point it will not bias and ruin these KT88s as well. I am getting so paranoid about it that I would swear that all the tubes seem a little too bright There is a schematic of the amp at this site ARCDB - M-100 . As I said any input would be greatly appreciated.
Thanks
Tom Wild
I have a pair of M100s too. They are among the best sounding ARC amps but extremely finicky. They are running with all devices of the regulators on their edges. Anything could go wrong at anytime. Most of the problems I experienced were on the power supplies and regulators.
I would suggest you take off all output tubes and check if all the power supplies and regulators work properly. The schematic includes the dc voltages of all regulators' output. I suspect the voltage at screen grid no 1 has gone wrong.
I would suggest you take off all output tubes and check if all the power supplies and regulators work properly. The schematic includes the dc voltages of all regulators' output. I suspect the voltage at screen grid no 1 has gone wrong.
Hi Prakit,
I appreciate your input and you seem to be fairly knowledgeable about this amp. The first thing is I need to do is decide whether to fix them or send them back. Is it possible that this problem has damaged all tubes and other components in the amplification stages or will the damage just be associated with the output tubes? What and where exactly is screen grid no, 1? Is this the 6550 tube in the power supply that they are calling the "Screen Regulator" and I have talked about getting too hot? As you can see I am definitely a newbie but willing to put out some effort. If I do decide to keep them I will probably have time this weekend to look at them and perform these voltage checks. Until then.
Thanks so much,
WILD1
I appreciate your input and you seem to be fairly knowledgeable about this amp. The first thing is I need to do is decide whether to fix them or send them back. Is it possible that this problem has damaged all tubes and other components in the amplification stages or will the damage just be associated with the output tubes? What and where exactly is screen grid no, 1? Is this the 6550 tube in the power supply that they are calling the "Screen Regulator" and I have talked about getting too hot? As you can see I am definitely a newbie but willing to put out some effort. If I do decide to keep them I will probably have time this weekend to look at them and perform these voltage checks. Until then.
Thanks so much,
WILD1
Hey Guys,
I did the voltage checks as you suggested Prakit and I had high readings for the voltage coming from the transformers and going to the 6550 regulators anode and screen. The schematic says that the voltage should be +590. I am getting 736 volts for one amp and 685 volts for the other amp. The only other items in this line coming from the transformers are two resistors and the capacitors. The resistors on visual inspection look good. I will have to pull the capacitors out to get to them if I want to check them. Could bad capacitors cause this? They are 27 years old. The strange thing is that the control grids voltages are only at 270 and 258 and the voltages at the cathodes are 330 and 299. The schematic says the voltage at the cathode should be +340 so these values are not high. yet those values for the anode of a 6550 tube are over the limit.
Dazed and confused,
WILD1
P.S. Had some boys out at the ranch today hunting wild hogs. Now that would make a good barbecue!
I did the voltage checks as you suggested Prakit and I had high readings for the voltage coming from the transformers and going to the 6550 regulators anode and screen. The schematic says that the voltage should be +590. I am getting 736 volts for one amp and 685 volts for the other amp. The only other items in this line coming from the transformers are two resistors and the capacitors. The resistors on visual inspection look good. I will have to pull the capacitors out to get to them if I want to check them. Could bad capacitors cause this? They are 27 years old. The strange thing is that the control grids voltages are only at 270 and 258 and the voltages at the cathodes are 330 and 299. The schematic says the voltage at the cathode should be +340 so these values are not high. yet those values for the anode of a 6550 tube are over the limit.
Dazed and confused,
WILD1
P.S. Had some boys out at the ranch today hunting wild hogs. Now that would make a good barbecue!
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Be extremely careful with that amp and those power supply voltages. There is plenty enough energy in those supplies to kill you several times over. The caps will retain a charge until they have time to bleed down, so the amp is dangerous for a time even after you turn it off. I don't want to sound like somebody's mom, but non-experienced people servicing hi-voltage tube gear worry me.
Great amp by the way. I really like that era ARC tube stuff.
Great amp by the way. I really like that era ARC tube stuff.
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Now that I'm done with the safety lecture... According to the schematic at arcdb.ws, there should be about 630V feeding the plates of the regulator tubes (through resistors). Looks to me like the 630V comes from laddering the transformer's rectified DC output. It is hard for me to picture how you're getting those high voltages right off the transformer. Could it be caps? I'm guessing not likely, but a quick look at them with a scope would tell you if they're shot. This is a really complex power supply, and I wouldn't want to troubleshoot it without proper tools (and one hand behind my back).
I've got a D90 which was re-capped a couple of years ago, along with new tubes and a general tune up, and I love the thing. I'd recommend that for an amp this old - it's worth it and it should last another twenty-some years before it needs it again.
I've got a D90 which was re-capped a couple of years ago, along with new tubes and a general tune up, and I love the thing. I'd recommend that for an amp this old - it's worth it and it should last another twenty-some years before it needs it again.
WOW!
Appreciate the input. Please keep it coming. Those B+ voltage readings are with all tubes installed and no signal. I first tested them with no output tubes installed and when I got high voltages I thought the same thing no load. But when I put the tubes back in voltages did not change. As far as working with high voltages, I had my father standing there with a walking stick so if it got me he could knock me off of it. I get bit on the ranch at least once a month by the electric fences. Eight to eleven thousand volts. It will make your teeth hurt. However it is a pulsating current with very low amperage not a DC regulated current like this. As far as the charge on the capacitors they have already drained down and I was working on the amps this evening. Less than four hours.
Thanks again,
WILD1
Appreciate the input. Please keep it coming. Those B+ voltage readings are with all tubes installed and no signal. I first tested them with no output tubes installed and when I got high voltages I thought the same thing no load. But when I put the tubes back in voltages did not change. As far as working with high voltages, I had my father standing there with a walking stick so if it got me he could knock me off of it. I get bit on the ranch at least once a month by the electric fences. Eight to eleven thousand volts. It will make your teeth hurt. However it is a pulsating current with very low amperage not a DC regulated current like this. As far as the charge on the capacitors they have already drained down and I was working on the amps this evening. Less than four hours.
Thanks again,
WILD1
Hi Jim,
I appreciate the input. I have been looking at a more recent version of the schematic. Not near as detailed as the one at the ARC website. Also like I said it showed 590 volts at the Regulators plate and screen grid. The voltages I gave were after the small resistors, however at ten and 100 ohms I don't think they change the voltage very much. I also checked the resistance of these resistors as well as the two before the control grid.They were all fine. I can not believe they are using this tube even at 630 volts. On a spec sheet by Tungsol for a 6550 maximum plate voltage recommended is 600 and screen voltage is 400. I am starting to believe Prakit that this power supply is running Balls out. I had another person tell me that yes they are great amps but be prepared to replace output and regulator tubes every two years. In his words "It eats output tubes." They are rated at a modest 100 Watts but at 16ohms. The little I have listened to them I think they are incredible The Bass is unbelievable for a tube amp. I still would sure like to calm down that output voltage from the transformer. If any one has any suggestions please let me know.
Hasta Luego,
WILD1
I appreciate the input. I have been looking at a more recent version of the schematic. Not near as detailed as the one at the ARC website. Also like I said it showed 590 volts at the Regulators plate and screen grid. The voltages I gave were after the small resistors, however at ten and 100 ohms I don't think they change the voltage very much. I also checked the resistance of these resistors as well as the two before the control grid.They were all fine. I can not believe they are using this tube even at 630 volts. On a spec sheet by Tungsol for a 6550 maximum plate voltage recommended is 600 and screen voltage is 400. I am starting to believe Prakit that this power supply is running Balls out. I had another person tell me that yes they are great amps but be prepared to replace output and regulator tubes every two years. In his words "It eats output tubes." They are rated at a modest 100 Watts but at 16ohms. The little I have listened to them I think they are incredible The Bass is unbelievable for a tube amp. I still would sure like to calm down that output voltage from the transformer. If any one has any suggestions please let me know.
Hasta Luego,
WILD1
Hi WILD1,
Some discrepancies of values between schematic and measurement are normal. But 736 V. and 590 V is too much diff. I would check the AC V for the secondaries for both units. If they are the same, very likely the trans are ok.
Since I don't think the caps are the culprit here, the v-dropping R could be bad.
I would also check all V out from other regulators while at it.
When I first received the M100, all voltage were off the spec quite a bit. It took me a full month or so to work on this problem. I suspected the resistance drifted after years in extremely hot environment.
Agree with the words of caution. Make sure that all caps are drain before fiddling around.
One of my M100 killed a thermistor a couple week ago. Still yet find time to work on it.
Good luck
Some discrepancies of values between schematic and measurement are normal. But 736 V. and 590 V is too much diff. I would check the AC V for the secondaries for both units. If they are the same, very likely the trans are ok.
Since I don't think the caps are the culprit here, the v-dropping R could be bad.
I would also check all V out from other regulators while at it.
When I first received the M100, all voltage were off the spec quite a bit. It took me a full month or so to work on this problem. I suspected the resistance drifted after years in extremely hot environment.
Agree with the words of caution. Make sure that all caps are drain before fiddling around.
One of my M100 killed a thermistor a couple week ago. Still yet find time to work on it.
Good luck
This amp has one of the most user-unservicable power supplies that I have ever seen. If it's more than tubes, and it sure sounds like that's the case, I would consider calling Audio Research to see if they would service and update the amps for you. Normally, I'm a big proponent of DIY, but there's a another reason aside from the complexity of the supplies and the fact that they will be running correctly when you get them back from ARC. These amps are classics and are collectible. If the amp has obviously been serviced by anyone but ARC, that will significantly reduce the value of the amp. It's probably an expensive proposition, but these amps are probably worth it.
Jim
Jim
"Build it and they will come"
Hi Jim,
Sending them to ARC is not an option. You know when I was looking for a power amp I read numerous blogs and if anyone had an unusual question or problem about the amps the answer was always the same." Call Lenard he will know" [The tech at ARC who has since retired]. Well when I started looking at them and I realized that I couldn't afford A new Cadillac I started looking at the older models. I called the tech at ARC to get some input and he acted like I was wasting his time. After I bought the amps I called about the mix match of tubes and what was used originally and he accused me of " picking his brain" and that I was then going to go buy tubes from someone else. So what! Knowledge is something that should be shared and irregardless he should stand behind ARC's products and give full support to owners of their products. But hey that's all right. I have been brought up with the philosophy that if you can't fix it or ride it you shouldn't own it. I let my father read the comments that have been posted. He thinks your all scared of electricity. But this is coming from an hombre that if we are out and don't have any way to check the voltage on a fence line, he checks it with his hand. 86 years old and still feeding the cows. Must be all that extra accumulation of energy. I checked on capacitors for the amp. $29.00 from Galco. Prakit I think your right . I need to slow down and check all resistors associated with those regulators. Most of them will not be that hard since pulling the tube takes them out of the circuit. Also check all voltages associated with them. I need to be more meticulous. As far as checking the AC output current of the transformers I might leave that to Mr. High Volts my dad. Although AC would definitely be a easier to get away from. I was always taught that it's current that kills. As far as destroying a classic, the shape these amps are in electronically [cosmetically they are a 10] they could not of found a better home and will never be on the market again. I'll try and work on them a few nights this week and this weekend.
Adios,
Tom Wild [WILD1]
Hi Jim,
Sending them to ARC is not an option. You know when I was looking for a power amp I read numerous blogs and if anyone had an unusual question or problem about the amps the answer was always the same." Call Lenard he will know" [The tech at ARC who has since retired]. Well when I started looking at them and I realized that I couldn't afford A new Cadillac I started looking at the older models. I called the tech at ARC to get some input and he acted like I was wasting his time. After I bought the amps I called about the mix match of tubes and what was used originally and he accused me of " picking his brain" and that I was then going to go buy tubes from someone else. So what! Knowledge is something that should be shared and irregardless he should stand behind ARC's products and give full support to owners of their products. But hey that's all right. I have been brought up with the philosophy that if you can't fix it or ride it you shouldn't own it. I let my father read the comments that have been posted. He thinks your all scared of electricity. But this is coming from an hombre that if we are out and don't have any way to check the voltage on a fence line, he checks it with his hand. 86 years old and still feeding the cows. Must be all that extra accumulation of energy. I checked on capacitors for the amp. $29.00 from Galco. Prakit I think your right . I need to slow down and check all resistors associated with those regulators. Most of them will not be that hard since pulling the tube takes them out of the circuit. Also check all voltages associated with them. I need to be more meticulous. As far as checking the AC output current of the transformers I might leave that to Mr. High Volts my dad. Although AC would definitely be a easier to get away from. I was always taught that it's current that kills. As far as destroying a classic, the shape these amps are in electronically [cosmetically they are a 10] they could not of found a better home and will never be on the market again. I'll try and work on them a few nights this week and this weekend.
Adios,
Tom Wild [WILD1]
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Comparing ARC to Cadillac is insulting them, they would fall into a more high end exotic group. I haven't talked to ARC in a couple of years, but they were decent to me and sent me a schematic for a SP-8. I wasn't asking for help, just documentation though. I know they're not cheap, but they know what they're doing and the amps will be done right.
As for working with high voltage, I've done a lot of that and getting nailed by a high voltage DC supply with essentially unlimited current is a lot different than an electric fence. It's potentially fatal.
It's obvious that you have at least some knowledge of tube electronics. The hunt-and-peck approach on a supply this complicated might or might not get your amps fixed. I hope you're lucky, but persistence and learning will get you there too. This project is a little like learning car mechanics by rebuilding an engine.
For your too-high voltage at the start of the power supply, that is, before the regulators, I'd start at the beginning: figure out what the AC voltages coming out of the transformers should be, and confirm that they are correct.
Good luck,
Jim
As for working with high voltage, I've done a lot of that and getting nailed by a high voltage DC supply with essentially unlimited current is a lot different than an electric fence. It's potentially fatal.
It's obvious that you have at least some knowledge of tube electronics. The hunt-and-peck approach on a supply this complicated might or might not get your amps fixed. I hope you're lucky, but persistence and learning will get you there too. This project is a little like learning car mechanics by rebuilding an engine.
For your too-high voltage at the start of the power supply, that is, before the regulators, I'd start at the beginning: figure out what the AC voltages coming out of the transformers should be, and confirm that they are correct.
Good luck,
Jim
"Hi Jim, Sending them to ARC is not an option.
I called the tech at ARC to get some input and he acted like I was wasting his time."
thats to bad, i don't blame you.
"I let my father read the comments that have been posted. He thinks your all scared of electricity. But this is coming from an hombre that if we are out and don't have any way to check the voltage on a fence line, he checks it with his hand. 86 years old and still feeding the cows. Must be all that extra accumulation of energy."
maybe. although i was an electrician for some years in ft.worth. and we delt with some pretty high voltages, we called 220 low voltage.
"As far as checking the AC output current of the transformers I might leave that to Mr. High Volts my dad."
please remind him he didnt get to 86 being stupid. we would hate for anyone to get killed.
"Although AC would definitely be a easier to get away from. I was always taught that it's current that kills."
true, i forget if its .003A or .030A through the heart that is fatal.
maybe someone will chime in.
the avrage person has about 2kohms res @ 220v and 1.5k @ 1kv.
ohm law .6666A @ 1kv = dead
.11A @ 220v = dead
wikapedia.........
60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation
I called the tech at ARC to get some input and he acted like I was wasting his time."
thats to bad, i don't blame you.
"I let my father read the comments that have been posted. He thinks your all scared of electricity. But this is coming from an hombre that if we are out and don't have any way to check the voltage on a fence line, he checks it with his hand. 86 years old and still feeding the cows. Must be all that extra accumulation of energy."
maybe. although i was an electrician for some years in ft.worth. and we delt with some pretty high voltages, we called 220 low voltage.
"As far as checking the AC output current of the transformers I might leave that to Mr. High Volts my dad."
please remind him he didnt get to 86 being stupid. we would hate for anyone to get killed.
"Although AC would definitely be a easier to get away from. I was always taught that it's current that kills."
true, i forget if its .003A or .030A through the heart that is fatal.
maybe someone will chime in.
the avrage person has about 2kohms res @ 220v and 1.5k @ 1kv.
ohm law .6666A @ 1kv = dead
.11A @ 220v = dead
wikapedia.........
60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation
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What is better to show fear or respect
Hey guys,
I think your confusing being scared with having respect. I think that is what my father meant. It doesn't help to be scared of high voltage [that will only get you hurt] nor for that matter being scared of anything you are working with be it a table saw or 50 1200 lb cows in a corral or high voltage power supplies. But do respect it and take the necessary precautions. So yes we do respect electricity and I will continue to take the precautions necessary but I will not let it scare me. As far as the AC voltage coming from the transformers. I already checked it as Prakit suggested. At least the leads supplying the voltage I am concerned about. Both transformers are exactly the same 327 volts and 163 volts. Now I don't have the specs and since I can't expect help from ARC, them being the same will have to suffice. It really was not that tough. Pulled the bottom panels and the leads were right there staring me in the face. Guess I got lucky. As far as the reference to Cadillacs, you really need to lighten up Jim. Its an expression. If I was to compare the M100s to any vehicle I think it would be a Ferrari. As Prakit said they are running on the edge. What the newer Arc equipment is like I have no idea. Oh well got to get back to work. Have a good evening.
Lluego,
WILD1
Hey guys,
I think your confusing being scared with having respect. I think that is what my father meant. It doesn't help to be scared of high voltage [that will only get you hurt] nor for that matter being scared of anything you are working with be it a table saw or 50 1200 lb cows in a corral or high voltage power supplies. But do respect it and take the necessary precautions. So yes we do respect electricity and I will continue to take the precautions necessary but I will not let it scare me. As far as the AC voltage coming from the transformers. I already checked it as Prakit suggested. At least the leads supplying the voltage I am concerned about. Both transformers are exactly the same 327 volts and 163 volts. Now I don't have the specs and since I can't expect help from ARC, them being the same will have to suffice. It really was not that tough. Pulled the bottom panels and the leads were right there staring me in the face. Guess I got lucky. As far as the reference to Cadillacs, you really need to lighten up Jim. Its an expression. If I was to compare the M100s to any vehicle I think it would be a Ferrari. As Prakit said they are running on the edge. What the newer Arc equipment is like I have no idea. Oh well got to get back to work. Have a good evening.
Lluego,
WILD1
"I have been brought up with the philosophy that if you can't fix it or ride it you shouldn't own it."
This attitude is particularly applicable to owning a pair of ARC M100. They sound so good yet they **** from time to time. Relying on anyone else to fix them for you is a big hassle especially if you have to ship them back and forth.
Take your time to learn about it inside out. You will surely figure out what's wrong with it and be able to fix it eventually. You have another working amp as a reference.
Good luck
Prakit
This attitude is particularly applicable to owning a pair of ARC M100. They sound so good yet they **** from time to time. Relying on anyone else to fix them for you is a big hassle especially if you have to ship them back and forth.
Take your time to learn about it inside out. You will surely figure out what's wrong with it and be able to fix it eventually. You have another working amp as a reference.
Good luck
Prakit
Hey Prakit,
Kind of late here [11PM]. I didn't get off work till late and then got involved with the amps. I've got the power supply settled down. 647 Volts My source is 122 Volts so I imagine this is affecting it a little. I can live with this for now and yes it was a resistor. I am still having voltage problems at three places. The screen grid #1 [sound familiar,that's the first thing you told me you suspected] and one of the plates in the 12AT7 regulator. I believe that the voltage should be around 320 Volts and I am only getting 264 Volts. They are both associated with that 100K ohm resistor that sits right next to the 6550 regulator. I checked the resistance and it seems fine if anything a little low. But I remember what you said about your suspicions that the age and heat has affected them possibly. Do you think that they could be failing when it heats up? The third voltage problem is the cathode output from the 6550. On the sick amp it is only 299 volts. I have my suspicions that the the low voltage to the screen grid #1 is causing this. The good amp has 300 volts to the screen grid #1 and the cathode output is 330 Volts. On the money. You are so right about being able to use the other amp as a reference,it really helps. I would appreciate your input.
Thanks,
WILD1
Kind of late here [11PM]. I didn't get off work till late and then got involved with the amps. I've got the power supply settled down. 647 Volts My source is 122 Volts so I imagine this is affecting it a little. I can live with this for now and yes it was a resistor. I am still having voltage problems at three places. The screen grid #1 [sound familiar,that's the first thing you told me you suspected] and one of the plates in the 12AT7 regulator. I believe that the voltage should be around 320 Volts and I am only getting 264 Volts. They are both associated with that 100K ohm resistor that sits right next to the 6550 regulator. I checked the resistance and it seems fine if anything a little low. But I remember what you said about your suspicions that the age and heat has affected them possibly. Do you think that they could be failing when it heats up? The third voltage problem is the cathode output from the 6550. On the sick amp it is only 299 volts. I have my suspicions that the the low voltage to the screen grid #1 is causing this. The good amp has 300 volts to the screen grid #1 and the cathode output is 330 Volts. On the money. You are so right about being able to use the other amp as a reference,it really helps. I would appreciate your input.
Thanks,
WILD1
Hi Tom,
You want to check string of Zener diodes ZD12-19. You should get about 7x1N4756+1N4749=7X47+27=356V across it. I remember vaguely that I had to replace some of these zener in order to get proper voltages. There are a few zeners associated with the regulators. You want to check them too.
Best
Prakit
You want to check string of Zener diodes ZD12-19. You should get about 7x1N4756+1N4749=7X47+27=356V across it. I remember vaguely that I had to replace some of these zener in order to get proper voltages. There are a few zeners associated with the regulators. You want to check them too.
Best
Prakit
Hi Prakit
Okay ,after reading about zener diodes and their purpose I think I get it. They are basically being used as voltage regulators themselves. Pretty darn smart. The band would a played who'd a thunk it. My next question is if they are where I think they are [on the circuit board tucked underneath the chassis] how did you get to them? Taking the circuit board loose or going in from the bottom? Second , once you determined voltage was off how did you find the bad ones? By checking the voltage across each individual one? I think before this is over I'm going to owe you a few barbecues and bottles of Tequila.
Tom Wild [WILD1]
Nacogdoches Texas
Okay ,after reading about zener diodes and their purpose I think I get it. They are basically being used as voltage regulators themselves. Pretty darn smart. The band would a played who'd a thunk it. My next question is if they are where I think they are [on the circuit board tucked underneath the chassis] how did you get to them? Taking the circuit board loose or going in from the bottom? Second , once you determined voltage was off how did you find the bad ones? By checking the voltage across each individual one? I think before this is over I'm going to owe you a few barbecues and bottles of Tequila.
Tom Wild [WILD1]
Nacogdoches Texas
Yes, these are the zener located near the edge of the pcb on the transformers' side. They are very difficult to reach. But you can do the measurement on the copper side. First unplug the amp and check each and every zener with your multimeter set for diode checking. I hope you find a bad zener in this step.
If you don't find one then you will have to check if you get proper voltage across the string of the zener. You will have to power up the amp to do this measurement. Be very very careful here. You can take out all 6550 tubes including one in the regulator while doing this.
Good luck
Prakit
If you don't find one then you will have to check if you get proper voltage across the string of the zener. You will have to power up the amp to do this measurement. Be very very careful here. You can take out all 6550 tubes including one in the regulator while doing this.
Good luck
Prakit
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