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Dynaco ST-70 noise problem
Hi, Over the past ten years I've been incrementally upgrading a stock factory-wired Dynaco ST-70 which introduced me to the world of hollow-state audio. I'm to the point now where there aren't many original components left in the amplifier. But, I have a problem that is driving me nuts. First, a list of all mods I have done: 1. SDS Labs Capacitor board 2. Triode Electronics "Classic EF86" driver board (2xEF86, ECC82) 3. Replaced EL34 tube sockets and associated resistors 4. Replaced power cord, speaker connectors, line in connectors, removed mono/stereo switch. Amp had been rewired with a diode in place of the GZ34, I re-wired it back, so the GZ34 is in operation. In fact, it occurs to me that there are no original capacitors or resistors in the amplifier. The power transformer, output transformer, and bias pots are original. The problem: The right channel puts out a low-level quasi-random static/crackle with a background "rushing" pinkish noise when the amp has been on for a while. It comes and goes, but often persists once it starts. It is especially maddening when I am listening to soft music. The quality of the music does not seem to be affected by this problem - it's just there in the background. Here is what I've done as far as troubleshooting goes: 1. Twiddle bias pots to see if twiddling affects noise - nope. 2. Swapped EL34's - noise stays in right channel. 3. Swapped EF86's - noise stays in right channel. 4. Pull right EF86 - noise stays in right channel. 5. Pull ECC82 - noise GOES AWAY. In fact, it was only after beginning this message that I tried pulling the ECC82 tube, following the troubleshooting suggestions in the Triode Electronics literature that came with my driver board upgrade (which says pull all of the driver board tubes and see if the noise persists). I know it's probably not wise to pull tubes while the amp is running but the problem can take a long time to start after powering up! I had thought that I had narrowed it down to the bias pots (cheap to replace) and output transformers (not cheap to replace) but now I am beginning to suspect the driver board again. I have re-soldered connections on the driver board as well as swapped out the ECC82 tube with a new one - problem persists. I highly doubt both ECC82 tubes are bad but I suppose it is possible. This is my third ECC82 tube, come to think of it. I believe I sent one back to Triode Electronics a couple years ago when this problem first came up - maybe I sent back a good tube?? I would appreciate any suggestions. Leigh -- Leigh Orf http://orf.cx SDF Public Access UNIX System - http://sdf.lonestar.org |
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#2
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
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#3
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Leigh Orf wrote: Hi, Over the past ten years I've been incrementally upgrading a stock factory-wired Dynaco ST-70 which introduced me to the world of hollow-state audio. I'm to the point now where there aren't many original components left in the amplifier. But, I have a problem that is driving me nuts. First, a list of all mods I have done: 1. SDS Labs Capacitor board 2. Triode Electronics "Classic EF86" driver board (2xEF86, ECC82) 3. Replaced EL34 tube sockets and associated resistors 4. Replaced power cord, speaker connectors, line in connectors, removed mono/stereo switch. Amp had been rewired with a diode in place of the GZ34, I re-wired it back, so the GZ34 is in operation. In fact, it occurs to me that there are no original capacitors or resistors in the amplifier. The power transformer, output transformer, and bias pots are original. The problem: The right channel puts out a low-level quasi-random static/crackle with a background "rushing" pinkish noise when the amp has been on for a while. It comes and goes, but often persists once it starts. It is especially maddening when I am listening to soft music. The quality of the music does not seem to be affected by this problem - it's just there in the background. Here is what I've done as far as troubleshooting goes: 1. Twiddle bias pots to see if twiddling affects noise - nope. 2. Swapped EL34's - noise stays in right channel. 3. Swapped EF86's - noise stays in right channel. 4. Pull right EF86 - noise stays in right channel. 5. Pull ECC82 - noise GOES AWAY. In fact, it was only after beginning this message that I tried pulling the ECC82 tube, following the troubleshooting suggestions in the Triode Electronics literature that came with my driver board upgrade (which says pull all of the driver board tubes and see if the noise persists). I know it's probably not wise to pull tubes while the amp is running but the problem can take a long time to start after powering up! I had thought that I had narrowed it down to the bias pots (cheap to replace) and output transformers (not cheap to replace) but now I am beginning to suspect the driver board again. I have re-soldered connections on the driver board as well as swapped out the ECC82 tube with a new one - problem persists. I highly doubt both ECC82 tubes are bad but I suppose it is possible. This is my third ECC82 tube, come to think of it. I believe I sent one back to Triode Electronics a couple years ago when this problem first came up - maybe I sent back a good tube?? I would appreciate any suggestions. Leigh I've got the mod (I built it myself), and it's very quiet. I triode connected the ef86 on mine. It sounds like you may have a bad signal tube socket, or possibly a strand of wire may be brushing the chassis or something else. Pulling the 12au7 suggests the problem is signal related, coming from before or at the 12au7, or being fed back through the feedback loop. Check the feedback circuit for anything wrong. Try opening the feedback loop and see if the sound goes away. Good Luck Bob H. |
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#4
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Leigh Orf wrote
Over the past ten years I've been incrementally upgrading a stock factory-wired Dynaco ST-70 which introduced me to the world of hollow-state audio. I'm to the point now where there aren't many original components left in the amplifier. But, I have a problem that is driving me nuts. First, a list of all mods I have done: 1. SDS Labs Capacitor board 2. Triode Electronics "Classic EF86" driver board (2xEF86, ECC82) 3. Replaced EL34 tube sockets and associated resistors 4. Replaced power cord, speaker connectors, line in connectors, removed mono/stereo switch. Amp had been rewired with a diode in place of the GZ34, I re-wired it back, so the GZ34 is in operation. In fact, it occurs to me that there are no original capacitors or resistors in the amplifier. The power transformer, output transformer, and bias pots are original. The problem: The right channel puts out a low-level quasi-random static/crackle with a background "rushing" pinkish noise when the amp has been on for a while. It comes and goes, but often persists once it starts. It is especially maddening when I am listening to soft music. The quality of the music does not seem to be affected by this problem - it's just there in the background. Here is what I've done as far as troubleshooting goes: 1. Twiddle bias pots to see if twiddling affects noise - nope. 2. Swapped EL34's - noise stays in right channel. 3. Swapped EF86's - noise stays in right channel. 4. Pull right EF86 - noise stays in right channel. 5. Pull ECC82 - noise GOES AWAY. In fact, it was only after beginning this message that I tried pulling the ECC82 tube, following the troubleshooting suggestions in the Triode Electronics literature that came with my driver board upgrade (which says pull all of the driver board tubes and see if the noise persists). I know it's probably not wise to pull tubes while the amp is running but the problem can take a long time to start after powering up! I had thought that I had narrowed it down to the bias pots (cheap to replace) and output transformers (not cheap to replace) but now I am beginning to suspect the driver board again. I have re-soldered connections on the driver board as well as swapped out the ECC82 tube with a new one - problem persists. I highly doubt both ECC82 tubes are bad but I suppose it is possible. This is my third ECC82 tube, come to think of it. I believe I sent one back to Triode Electronics a couple years ago when this problem first came up - maybe I sent back a good tube?? I would appreciate any suggestions. Looking at the original circuit diagram, http://www.curcioaudio.com/st7_mnl.pdf the ECC82 is used as a concertina phase splitter for each channel. The only associated components are the two 47k load resistors and the two coupling caps. If pulling the pentodes makes no difference to the noise, but pulling the ECC82 does, then the chances are that the valve is at fault. Possibly an internal short. Possibly heater/cathode due to poor valve and voltage difference due to elevated cathode. Easiest thing would be to swap the ECC82. You'll need another someday anyway, so you may as well get one now. A longer shot is a failing coupling cap, as this would also be relieved by removing the ECC82. Presumably they are plastic caps though, and I can't see how they could be responsible for the fault you describe. Other than that, as others have suggested, a dry solder joint, cracked trace or broken resistor associated with the ECC82 could be failing as the amp warms up. Up to the point when it went awry, BTW, were all those mods worthwhile? cheers, Ian |
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#5
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Leigh Orf wrote: Hiss-crackle-pop w/an ST-70, right channel. Betcha dollars to green M&Ms that you have a poor connection somewhere. Either a broken trace, cold solder, bad tube pin, bad socket or similar. Most especially as it is confined to a single channel. Note that this could just as easily be a factory solder *or trace* on the board as anything you did. I keep an ST-70 as well, with the OEM phenolic driver board. However there is not much on that board that is original (caps or resistors), nor are the traces original either... each one is 'traced' with a strand of copper wire against breaks. Such parts (relative to all things) are cheap such that 1% tolerance and channel-to-channel matching is no trick and makes for nice stability overall. Unless you are using Chinese tubes, that is. If so, all bets are off. I feel about Chinese tubes much as Bret feels about the ST-70 in general. It is possible that the Chinese may make a decent tube, just not very likely. Peter Wieck Wyncote, PA |
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#6
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Ian Iveson wrote:
Looking at the original circuit diagram, http://www.curcioaudio.com/st7_mnl.pdf the ECC82 is used as a concertina phase splitter for each channel. The only associated components are the two 47k load resistors and the two coupling caps. If pulling the pentodes makes no difference to the noise, but pulling the ECC82 does, then the chances are that the valve is at fault. Possibly an internal short. Possibly heater/cathode due to poor valve and voltage difference due to elevated cathode. Easiest thing would be to swap the ECC82. You'll need another someday anyway, so you may as well get one now. The thing is, I did just that! The new tube exhibited the same behavior. Unless both tubes are bad, and in a similar way, the tube is off the hook. A longer shot is a failing coupling cap, as this would also be relieved by removing the ECC82. Presumably they are plastic caps though, and I can't see how they could be responsible for the fault you describe. The coupling caps are new (fat orange) Sprague capacitors, FYI. I will go back in and heat up solder joints ... again ... try some contact cleaner (on brand new tubes in brand new gold plated tube sockets)... and if it persists I will start replacing the circuitry around the tube as suggested by another poster. Intermittents suck! Other than that, as others have suggested, a dry solder joint, cracked trace or broken resistor associated with the ECC82 could be failing as the amp warms up. Up to the point when it went awry, BTW, were all those mods worthwhile? The short answer is yes, I am very happy with the final sound of the amp, although it has been plagued with intermittent noise of one sort or another since day one. This project has been a hobby as much as a quest to get decent affordable audio (I'm a ham radio operator / scientist and like getting the soldering iron out and building things). The original amp had the usual problems you'd expect - even more noise from the 7199 tube sockets - so the driver board was the first to be replaced. I forget exactly what motivated me to replace the power supply ciruitry. The power tube socket replacements was due to one of the pins breaking off due to my own incompetence (whoops) but in my own defense the original tabs were pretty flimsy. I figured "for symmetry" and for the hell of it I'd replace all four. Long ago I decided that I was not going to be a bonifide audiophile because it is too expensive and somewhat of a fool's errand where infinitessimal improvements come at exponential prices, and in fact I go out of my way to avoid listening to high-end stereo systems because of the possible virus it will implant inside of me (must upgrade... must upgrade...). But I will say this: the original magic that turned me on to this hobby when I first hooked up this amp, with its dying Mullard tubes, to my ProAc Super Tablettes is still there with the modded amp. If anything, the amp today is much "clearer", revealing more especially in the high frequencies than the original amp, and hence is less "mellow" but my ears have gotten used to this (and it's probalby more accurate anyway). There are times when I am listening and when I get goosebumps... and occasionally I find myself looking over my shoulder to see if my wife has snuck up behind me... there's that hard-to-quantify magic that I've never experienced with a SS amp that makes me want to listen more. And then I hear that damned crackle and want to get the shotgun out. I have seriously considered replacing it with another similarly powered tube amp, perhaps a kit... especially when hunting for intermittents gets to be no fun anymore. But I'm not quite there yet. I appreciate all of the suggestions from everyone. Leigh cheers, Ian -- Leigh Orf http://orf.cx SDF Public Access UNIX System - http://sdf.lonestar.org |
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#7
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
The right channel puts out a low-level quasi-random static/crackle with a background "rushing" pinkish noise when the amp has been on for a while. It comes and goes, but often persists once it starts. It is especially maddening when I am listening to soft music. The quality of the music does not seem to be affected by this problem - it's just there in the background. Here is what I've done as far as troubleshooting goes: I know it's probably not wise to pull tubes while the amp is running but the problem can take a long time to start after powering up! If the problem doesn't show up for a while, it could be heat-related. Also, a plate resistor could be shorting internally. This can happen in old radios. Either replacing all the plate resistors, or listening with a plastic tube can find it. Replacing them is easier. Also, try swapping the bias pots between channels. Old pots can be a problem. Sometimes they just go bad. I just replaced them in my amp, since they aren't expensive. Another thing which has gotten me, but is a longshot: check where the transformer leads go through the chassis holes, and make sure you don't have a partial short there. I had this happen once. Bob H. |
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#8
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Bratwig said:
My guess is that China DOES make decent tubes....but for the most part they stay in China, we get the off-fall. Some of the "boutique" products, particularly the mesh plate triodes and such, seem to be holding up fairly well, consistent with my theory that the older the tube type the easier it is to manufacture well. In America you had thirty or so separate tube companies manufacturing early receiving tubes, some of which could easily be duplicated by any college science department support shop today. It's later types like subminis, Compactrons and Nuvistors that would be a double bitch to reproduce today. Rubbish. They can make anything you want, as long as you specify how and what, and are willing to buy it by the millions. China is no longer a manufacturer of second-rate goods, it's about time we take them seriously. At the same time, we should be prepared to *pay* for good quality. Most people don't want that, even in our tube community. They just want $300 performance for $10. Sorry, it just doesn't work that way. Not even with products from China. -- - Maggies are an addiction for life. - |
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#9
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Sander deWaal wrote: They just want $300 performance for $10. Sorry, it just doesn't work that way. Not even with products from China. Sander: Sadly, even our tube community does not understand the market at all. It is not so much the $10-to-get-$300 issue as the issue of 'if it costs more, it must be better'. If North America is take as the measuring point, something over 1/2 billion (yep, that many) tube-consumer items were manufactured between 1923 and 1961 alone. This would include radios, televisions, audio, baby monitors (Yep, baby monitors since 1938), and so forth. Trillions of tubes were manufactured, some still are being made. Good US-made tubes are readily available here at prices that are pretty piddly as compared to some of the things they go into. Common tubes are sourced from China _because_ they are cheap. And the Chinese minimize quality control because they can and still get paid enough to make a profit. There are a few factories which do try harder and provide a decent product... at prices approaching tubes sourced from elsewhere, so the Chinese advantage is lost. But Groove Tube and their ilk may continue to sell crap because they have the price-point to do so, and because the Great Unwashed (now as in the past) are brainwashed into believing that tubes wear much faster than (at least good ones) actually do, and should be changed based on intervals rather than actual performance or wear. And that behavior is what supports the crap that comes out of China or anywhere else focused on the price-point rather than actual peformance. What's worse is the crappy sound that comes out of these tubes becomes some sort of esoteric standard.... In a way similar to the emasculation of speakers in general. To the point where there are many who believe that 'good sound' can come out of a pair of computer speakers just because "Bose" or "Harmon Kardon" or "Advent" is printed on them. End rant. Peter Wieck Wyncote, PA |
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#10
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
"Peter Wieck" said:
snip rant which, sadly, seems spot on There are a few factories which do try harder and provide a decent product... at prices approaching tubes sourced from elsewhere, so the Chinese advantage is lost. This is absolutely true, not only for tubes, but for many more products. There will always be a market for quality goods, and the Chinese are able and even willing to make them. We have to ask ourselves: are *we* willing to pay the right prices for them? Remember how much a single amplifier or receiver cost in 1970...... "The Great Unwashed"........you got that right. -- - Maggies are an addiction for life. - |
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#11
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Leigh wrote
Up to the point when it went awry, BTW, were all those mods worthwhile? The short answer is yes, I am very happy with the final sound of the amp, although it has been plagued with intermittent noise of one sort or another since day one. This project has been a hobby as much as a quest to get decent affordable audio (I'm a ham radio operator / scientist and like getting the soldering iron out and building things). The original amp had the usual problems you'd expect - even more noise from the 7199 tube sockets - so the driver board was the first to be replaced. I forget exactly what motivated me to replace the power supply ciruitry. The power tube socket replacements was due to one of the pins breaking off due to my own incompetence (whoops) but in my own defense the original tabs were pretty flimsy. I figured "for symmetry" and for the hell of it I'd replace all four. Long ago I decided that I was not going to be a bonifide audiophile because it is too expensive and somewhat of a fool's errand where infinitessimal improvements come at exponential prices, and in fact I go out of my way to avoid listening to high-end stereo systems because of the possible virus it will implant inside of me (must upgrade... must upgrade...). But I will say this: the original magic that turned me on to this hobby when I first hooked up this amp, with its dying Mullard tubes, to my ProAc Super Tablettes is still there with the modded amp. If anything, the amp today is much "clearer", revealing more especially in the high frequencies than the original amp, and hence is less "mellow" but my ears have gotten used to this (and it's probalby more accurate anyway). There are times when I am listening and when I get goosebumps... and occasionally I find myself looking over my shoulder to see if my wife has snuck up behind me... there's that hard-to-quantify magic that I've never experienced with a SS amp that makes me want to listen more. And then I hear that damned crackle and want to get the shotgun out. I have seriously considered replacing it with another similarly powered tube amp, perhaps a kit... especially when hunting for intermittents gets to be no fun anymore. But I'm not quite there yet. I appreciate all of the suggestions from everyone. Thanks, interesting. Perhaps you could let us know what the problem was when you've found it. cheers, Ian |
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#12
Posted to rec.audio.tubes
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Dynaco ST-70 noise problem
Peter Wieck wrote:
Sander deWaal wrote: They just want $300 performance for $10. Sorry, it just doesn't work that way. Not even with products from China. Sander: Sadly, even our tube community does not understand the market at all. It is not so much the $10-to-get-$300 issue as the issue of 'if it costs more, it must be better'. If North America is take as the measuring point, something over 1/2 billion (yep, that many) tube-consumer items were manufactured between 1923 and 1961 alone. This would include radios, televisions, audio, baby monitors (Yep, baby monitors since 1938), and so forth. Trillions of tubes were manufactured, some still are being made. Good US-made tubes are readily available here at prices that are pretty piddly as compared to some of the things they go into. Common tubes are sourced from China _because_ they are cheap. And the Chinese minimize quality control because they can and still get paid enough to make a profit. There are a few factories which do try harder and provide a decent product... at prices approaching tubes sourced from elsewhere, so the Chinese advantage is lost. But Groove Tube and their ilk may continue to sell crap because they have the price-point to do so, and because the Great Unwashed (now as in the past) are brainwashed into believing that tubes wear much faster than (at least good ones) actually do, and should be changed based on intervals rather than actual performance or wear. And that behavior is what supports the crap that comes out of China or anywhere else focused on the price-point rather than actual peformance. What's worse is the crappy sound that comes out of these tubes becomes some sort of esoteric standard.... In a way similar to the emasculation of speakers in general. To the point where there are many who believe that 'good sound' can come out of a pair of computer speakers just because "Bose" or "Harmon Kardon" or "Advent" is printed on them. Or worse yet... Altec Lansing! Hard to believe all that's left of it is this plastic detritus.... Roger Roger Anderson Assoc Ed Vacuum Tube Valley Magazine End rant. Peter Wieck Wyncote, PA |
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