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#81
Posted to rec.audio.tubes
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what is causing this problem?
In the guitar amp built for nephew I also used a 'single' connection on the bias pot wiper but the configuration is different. The pot ends go to -Bias and the grid resistor with the wiper going to ground through another resistor. -Bias through the pot and ground resistor then forms a variable divider but if the wiper breaks contact bias goes full negative so it's 'fail safe'. Excellent! |
#82
Posted to rec.audio.tubes
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what is causing this problem?
bigwig wrote in
: On 6 Dec, 23:24, Peter Wieck wrote: On Dec 6, 4:35*pm, mick wrote: On Sat, 06 Dec 2008 15:18:51 -0600, cipher wrote: snip Sir, I will take good detailed pictures and post them up. who around these parts would be able to work on my amp? Around Mordor? Saruman Electronics, I suppose... Give him a *Ring*! im sure most of you could, but who would?? Difficult to guess when no-one knows where you are, isn't it? I suck at soldering, so id rather send it so someone that wont look l ike a monkey ****ing a football. Have you got, perhaps, a local guitar amp repair place or, maybe, a rad io amateur or someone like that who might do it? There's a valid email address on my web site (Feedback and Links page) if you want to take this off-group. -- Mick * * * * * * * * * * *(Working in a M$-free z one!) Web:http://www.nascom.info Filtering everything posted from googlegroups to kill spam. * * He is in Florida - and he would have to ship the amp anyway. So, as far as practicalities are concerned, the Continental US is all the same to him. I would be glad to do it, if he didn't mind waiting 30 - 90 days, as that is about how long it takes me to get to any fresh project these days. Peter Wieck Melrose Park, PA- Hide quoted text - - Show quoted text - Cipher, If you mean Twickenham UK. Then try John at http://www.chambonino.com/ He is the guy. Your amp really does look rough. What is the switch on the back panel in the middle of the warning label?. The fault is clearly a bias problem but looking at the state of the thing it has more wrong than that, its a mess. Dont be disheartened by this the transformers and all major components should be fine. You could just go mad and strip it right down. You then have no option but to learn. A great way to get into valve gear!. This is what I would do. Matt. Hey Sir, I am in Wilmington, North Carolina. My buddy Mick is in the UK, and I Spent some time there with NATO, but now I just get my mic preamps there. Sorry for any confusion! |
#83
Posted to rec.audio.tubes
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what is causing this problem?
Paul G. wrote in
: On Sat, 6 Dec 2008 05:18:46 -0800 (PST), fryzz wrote: ....snip!..... I'm guessing you have an intermittent bias problem. Your amp has a separate bias supply, so the 68 ohm resistors are mostly just a convenient way of adjusting the idle current. If those bypass capacitors on the 68 ohm jobs are leaky, it would actually have the effect of increasing the negative voltage on the grid, which reduces the idle current, so that's not why the tubes would draw too much current. The first thing I would look at is the bias potentiometers, pots do tend to be trouble prone due to the moving parts. You could try cleaning them with something like Caig Deoxit. You might also try feeling those two filter caps in the bias supply after the amp has been on for a while. They'll pick up some heat just from being in a tubeamp, but if one is warmer than the other it's a sign that cap is leaking. Another thing you might try is touching up all of the solder joints in the bias supply. You might also just leave your multimeter hooked up, to see if the output of the bias supply is dropping when the amp gets that "close encounters" look. When you measure the output of the bias supply, it should be stable and noise free. The fact that just ONE tube goes red, and not the pair, suggests that the bias supply & adjustment is not a problem, since both tubes on each channel run off the same connection. If it is just the one tube that goes, and it's always the same socket (even if you switch tubes around), then I'd zero in on the socket, or the traces on the circuit board. That will require very careful inspection, resoldering, or possibly checking the springiness of the socket contacts. Since the socket gets alternately hot and cold with the accompanying expansion/contraction, it is very common for the socket contacts to break away from the circuit board. This is one of those applications where point-to-point wiring can be more reliable than circuit boards. I worked at RCA when they made tube sets..... there was no end of troubles with printed circuits and tube sockets that were soldered into them. I would also solder over the solder traces in case there was a crack in the board. That might not be practical, since most mfr.'s put stuff over the traces so when the boards are soldered, it won't adhere and waste solder. Very carefully inspect all the connections and traces between grid (pin 5) of the EL34's and the bias control. Make sure nothing is loose. If the caps in parallel with the 68 ohms were to get real leaky and short, the tube might get red, but the resistors would not cook (the caps would shunt all the current). My guess is your problem is in the grid circuit of the tube that cooks. If the 0.68 uF caps were to fail and break down, you would see symptoms similiar to what you're experiencing. Also if "R1K" and "R220K" in the grid circuits were to open up, you would get similiar behaviour. That's not very common for resistors, unless they have been mechanically abused. "Opening up" by a poor solder connection, thermal expansion, or bad trace would do the same (and more common). I also assume that this unit unit used common solder with tin/lead, and not the lead free (ROHS) kind. The lead free solder is not as reliable (critical equipment can duck out of the lead-free requirements!). How old is this unit? Did the manuals make any remark about being lead-free? A possible problem (but not likely, since the mfr. should have run into this) is that the system could be oscillating at some very high frequency. There are already grid stoppers, I'd be paranoid and put stoppers (100 ohms) in the screen circuit. If it did oscillate, probably both tubes would run red, and from your symptoms, that hasn't ocurred. I don't think you need this, but I would solder a resistor (100K) from the wiper of the bias pot to the (-) end where the cap is. If the wiper failed to make contact (as they do when dirty), you will still maintain a bias that won't destroy anything. Once you got mad in a previous post, and put down all the symptoms, it became a lot easier to troubleshoot. Just to make sure, is it just ONE tube that goes at a time? Does the same resistor cook each time? If so, it's probably a circuit issue. If the problem moves around, it MIGHT be a tube problem. Usually when I have a customer bringing in a naughty piece of equipment, it takes a few minutes of careful questioning to pin down the problem. Just a list of symptoms from the customer aren't enough..... I usually run them through what is for me a "troubleshooting tree". Knowing the history of the unit, what it does when naughty, what it does when you wack it (that's inevitable) helps enormously. The fact that it misbehaves intermittently makes it very difficult to service, and even more dependent on knowing the unit. Chances are, that on a bench, this thing could run properly for years! -Paul G. thanks for that info sir.. weird behaviour.... i hooked it up yesterday for a bit, with the tubes that I had used the day It went assed on me.... and now everything is running ok, or seems to be.... the same tube that was glowing bright red before is fine now, and the sound from both channels seems to be fine.. I am going to be sending this thing far away for someone to do it proper, hopefully one o you gents can take it on for me. I do not feel comfortable working on this thing.. it is the same resistors, and the same tube that goes up every time. is someone willing to take this on?? |
#84
Posted to rec.audio.tubes
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what is causing this problem?
"Ian Bell" wrote in message
Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Phil Allison wrote: "Ian Bell" So why have a completely transparent amp when the speakers and room are so relatively poor. ** Very accurate, low distortion speakers are readily available - but not necessarily cheap. The prices are coming down, and they are not prohibitive. Indeed, and there's the rub for most people. Treating a listening room so it does very little harm to the sound MORON. The whole point is that an untreated room does a lot of harm to the room. So resolved, if you have rotten speakers and a very poor, untreated room, then tubed audio is for you! No, all I said was a transparent amp in an already seriously flawed system is pointless. Right, but since when is our pursuit of the audio hobby about intentionally using a seriously flawed system? Who said intentionally? The average hi-fi person does not have a clue about acoustics. Since when do any of us aspire to the like the average hi fi person? |
#85
Posted to rec.audio.tubes
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what is causing this problem?
On Dec 7, 3:47*pm, cipher wrote:
Paul G. wrote : On Sat, 6 Dec 2008 05:18:46 -0800 (PST), fryzz wrote: ....snip!..... I'm guessing you have an intermittent bias problem. *Your amp has a separate bias supply, so the 68 ohm resistors are mostly just a convenient way of adjusting the idle current. *If those bypass capacitors on the 68 ohm jobs are leaky, it would actually have the effect of increasing the negative voltage on the grid, which reduces the idle current, so that's not why the tubes would draw too much current. The first thing I would look at is the bias potentiometers, pots do tend to be trouble prone due to the moving parts. *You could try cleaning them with something like Caig Deoxit. *You might also try feeling those two filter caps in the bias supply after the amp has been on for a while. *They'll pick up some heat just from being in a tubeamp, but if one is warmer than the other it's a sign that cap is leaking. *Another thing you might try is touching up all of the solder joints in the bias supply. *You might also just leave your multimeter hooked up, to see if the output of the bias supply is dropping when the amp gets that "close encounters" look. *When you measure the output of the bias supply, it should be stable and noise free. * *The fact that just ONE tube goes red, and not the pair, suggests that the bias supply & adjustment is not a problem, since both tubes on each channel run off the same connection. If it is just the one tube that goes, and it's always the same socket (even if you switch tubes around), then I'd zero in on the socket, or the traces on the circuit board. That will require very careful inspection, resoldering, or possibly checking the springiness of the socket contacts. Since the socket gets alternately hot and cold with the accompanying expansion/contraction, it is very common for the socket contacts to break away from the circuit board. This is one of those applications where point-to-point wiring can be more reliable than circuit boards. I worked at RCA when they made tube sets..... there was no end of troubles with printed circuits and tube sockets that were soldered into them. I would also solder over the solder traces in case there was a crack in the board. That might not be practical, since most mfr.'s put stuff over the traces so when the boards are soldered, it won't adhere and waste solder. * *Very carefully inspect all the connections and traces between grid (pin 5) of the EL34's and the bias control. Make sure nothing is loose. * *If the caps in parallel with the 68 ohms were to get real leaky and short, the tube might get red, but the resistors would not cook (the caps would shunt all the current). My guess is your problem is in the grid circuit of the tube that cooks. * *If the 0.68 uF caps were to fail and break down, you would see symptoms similiar to what you're experiencing. Also if "R1K" and "R220K" in the grid circuits were to open up, you would get similiar behaviour. That's not very common for resistors, unless they have been mechanically abused. "Opening up" by a poor solder connection, thermal expansion, or bad trace would do the same (and more common). * *I also assume that this unit unit used common solder with tin/lead, and not the lead free (ROHS) kind. The lead free solder is not as reliable (critical equipment can duck out of the lead-free requirements!). How old is this unit? Did the manuals make any remark about being lead-free? * *A possible problem (but not likely, since the mfr. should have run into this) is that the system could be oscillating at some very high frequency. There are already grid stoppers, I'd be paranoid and put stoppers (100 ohms) in the screen circuit. If it did oscillate, probably both tubes would run red, and from your symptoms, that hasn't ocurred. * *I don't think you need this, but I would solder a resistor (100K) from the wiper of the bias pot to the (-) end where the cap is. If the wiper failed to make contact (as they do when dirty), you will still maintain a bias that won't destroy anything. * Once you got mad in a previous post, and put down all the symptoms, it became a lot easier to troubleshoot. Just to make sure, is it just ONE tube that goes at a time? Does the same resistor cook each time? If so, it's probably a circuit issue. If the problem moves around, it MIGHT be a tube problem. * *Usually when I have a customer bringing in a naughty piece of equipment, it takes a few minutes of careful questioning to pin down the problem. Just a list of symptoms from the customer aren't enough..... I usually run them through what is for me a "troubleshooting tree". Knowing the history of the unit, what it does when naughty, what it does when you wack it (that's inevitable) helps enormously. The fact that it misbehaves intermittently makes it very difficult to service, and even more dependent on knowing the unit. Chances are, that on a bench, this thing could run properly for years! -Paul G. thanks for that info sir.. weird behaviour.... i hooked it up yesterday for a bit, with the tubes that I had used the day It went assed on me.... and now everything is running ok, or seems to be.... the same tube that was glowing bright red before is fine now, and the sound from both channels seems to be fine.. I am going to be sending this thing far away for someone to do it proper, hopefully one o you gents can take it on for me. I do not feel comfortable working on this thing.. it is the same resistors, and the same tube that goes up every time. is someone willing to take this on??- Hide quoted text - - Show quoted text - If you don't mind waiting. You are third behind two other amps - and I just finished a receiver and a tuner that were with me for ~90 days. This is a hobby, so I get to it when I get to it. But, I do good work, or so I am told. How did those tubes work out, by the way? Peter Wieck Melrose Park, PA |
#86
Posted to rec.audio.tubes
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what is causing this problem?
On Dec 7, 7:58*pm, "Arny Krueger" wrote:
Since when do any of us aspire to the like the average hi fi person? Huh? Peter Wieck Melrose Park, PA |
#87
Posted to rec.audio.tubes
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what is causing this problem?
On Dec 7, 11:14 pm, flipper wrote:
On Sun, 7 Dec 2008 07:16:58 -0800 (PST), fryzz wrote: snip Excellent! Thank you. You're welcome. So 'half way better', regulating only one, is worse than nothing at all. I did not know that, thanks. Makes sense. |
#88
Posted to rec.audio.tubes
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what is causing this problem?
Arny Krueger wrote:
"Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Phil Allison wrote: "Ian Bell" So why have a completely transparent amp when the speakers and room are so relatively poor. ** Very accurate, low distortion speakers are readily available - but not necessarily cheap. The prices are coming down, and they are not prohibitive. Indeed, and there's the rub for most people. Treating a listening room so it does very little harm to the sound MORON. The whole point is that an untreated room does a lot of harm to the room. So resolved, if you have rotten speakers and a very poor, untreated room, then tubed audio is for you! No, all I said was a transparent amp in an already seriously flawed system is pointless. Right, but since when is our pursuit of the audio hobby about intentionally using a seriously flawed system? Who said intentionally? The average hi-fi person does not have a clue about acoustics. Since when do any of us aspire to the like the average hi fi person? Oh, so you think you are something better than that? Cheers Ian |
#89
Posted to rec.audio.tubes
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what is causing this problem?
"Ian Bell" wrote in message
Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: "Ian Bell" wrote in message Arny Krueger wrote: No, all I said was a transparent amp in an already seriously flawed system is pointless. Right, but since when is our pursuit of the audio hobby about intentionally using a seriously flawed system? Who said intentionally? The average hi-fi person does not have a clue about acoustics. Since when do any of us aspire to the like the average hi fi person? Oh, so you think you are something better than that? It's not a matter of being better (and your choice of works is both typical of you and revelatory), its a matter of being different. And yes, I am different than the average hi fi person. For openers, the average hi fi person misses my years of experience by a few decades, simply because on the average, they are far younger. |
#90
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