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Post by Boomzilla on Nov 1, 2022 15:54:51 GMT -5
I've a brand new tube amplifier using KT-88 output tubes. Every few minutes, one of the tubes exhibits a bright arc inside the tube with a tremendous popping noise at the amplifier outputs - then goes back to working properly. Since this is a new amp and a new tube, I'm suspecting that shipping damage has damaged this particular tube. Reasonable assumption?
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Post by audiobill on Nov 1, 2022 17:11:51 GMT -5
Try another KT88?
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Post by monkumonku on Nov 1, 2022 17:48:37 GMT -5
I've a brand new tube amplifier using KT-88 output tubes. Every few minutes, one of the tubes exhibits a bright arc inside the tube with a tremendous popping noise at the amplifier outputs - then goes back to working properly. Since this is a new amp and a new tube, I'm suspecting that shipping damage has damaged this particular tube. Reasonable assumption? If you want to chance it, switch the tubes to see if the arcing follows the tube. Then you know if it is the tube or the amp. |
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Post by Boomzilla on Nov 1, 2022 19:41:51 GMT -5
The manufacturer has two new, matched KT-88s in the mail.
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Post by 405x5 on Nov 1, 2022 21:51:31 GMT -5
Try a pair of solid state tubes….they are dandy!
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Post by Boomzilla on Nov 2, 2022 11:08:22 GMT -5
Try a pair of solid state tubes….they are dandy! Solid-state KT-88s seem hard to find... |
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KeithL
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Post by KeithL on Nov 3, 2022 8:49:57 GMT -5
The most likely cause is a defective tube... (it could be damaged or just plain bad). It also might be interesting to know if that particular amp is running those particular tubes very close to their voltage limit. Some amps run tubes at very high voltages, very near their maximum limit, to get the most power out of them. Or, while they claim to be compatible with multiple tube numbers, run some of them really close to, or even slightly above, their recommended maximum voltages. (Which can obviously be a problem if your tubes are less than perfect.) It's also worth noting that, on some simpler design, the plate voltage will vary depending on where you set the bias. If the bias is too high, and the plate current is too low, then the plate voltage may be higher than expected. (A good design would avoid this... but... ) I've a brand new tube amplifier using KT-88 output tubes. Every few minutes, one of the tubes exhibits a bright arc inside the tube with a tremendous popping noise at the amplifier outputs - then goes back to working properly. Since this is a new amp and a new tube, I'm suspecting that shipping damage has damaged this particular tube. Reasonable assumption? |
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Post by 405x5 on Nov 3, 2022 10:51:11 GMT -5
I would think with the technology being as old and obsolete as it is, that things like quality, control, and availability would be wreaking havoc on replacement tubes
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Post by vcautokid on Nov 3, 2022 11:01:51 GMT -5
Not to pimp PrimaLuna but if you were using one of those, output tubes never need biasing, and never run nearly as hard as other designs of similar money or more. Say like a Conrad Johnson which beats the schitt out of the output tubes not to mention it takes out the preceding circuitry before the tube when the tube dies or is defective. Nice! It is not unusual for a PrimaLuna to have output tubes last up to 10 years if you are not a diick about it. Or 5 years or so if you are.
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Post by AudioHTIT on Nov 3, 2022 12:01:50 GMT -5
Indeed, what does cause it?  |
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Post by 405x5 on Nov 3, 2022 13:26:10 GMT -5
Sometimes home theater is too realistic… I hate when my dog unexpectedly jumps off the couch and tries to bite the monitor…… Good boy |
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KeithL
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Post by KeithL on Nov 3, 2022 13:39:28 GMT -5
Just don't put up any pictures of fire hydrants.  Sometimes home theater is too realistic… I hate when my dog unexpectedly jumps off the couch and tries to bite the monitor…… Good boy |
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KeithL
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Post by KeithL on Nov 3, 2022 13:50:44 GMT -5
What can cause tube arcing: 1. Gas in the tube. (That can happen due to air leaking in through a crack or bad seal.) (It can also happen if poor quality metal surfaces inside release trace amounts of gases.) (It can also happen if certain metal surfaces get way too hot (they may then release gases that they otherwise wouldn't)). (The tube could simply have a weak vacuum due to poor manufacturing.) 2. Too high a plate voltage on the tube. (Some designers run their tubes really close to their safe voltage limit to squeeze a few more watts out of them.) (Some similar tubes, or even the same tube number from a different vendor, may have slightly different limits.) (The plate supplies in tube amps usually are not regulated, so they can drift if the line voltage changes, or if the current you draw from them changes.) (UNAUTHORIZED MODIFICATIONS. For example, if you substitute solid state rectifiers for a tube rectifier, it will usually raise the plate voltage significantly.) 3. A mechanical flaw or shipping damage. (Two parts got bent and are too close together.) (Or an insulator/spacer has become bent, loose, or cracked.) (With poor quality tubes you could even have small metal scraps or filings floating around inside.) |
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KeithL
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Post by KeithL on Nov 3, 2022 13:59:09 GMT -5
That too.... Back when tubes were current technology the quality control was actually quite good. However, nowadays, most "new/old stock" tubes are QUITE old... And the quality and quality control on a lot of new tubes is pretty bad. Of course there are at least a few companies currently turning out good quality tubes. (I don't keep track but you'll find plenty of discussions about that if you look around.) I would think with the technology being as old and obsolete as it is, that things like quality, control, and availability would be wreaking havoc on replacement tubes |
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Post by 405x5 on Nov 3, 2022 14:30:12 GMT -5
Just don't put up any pictures of fire hydrants. Sometimes home theater is too realistic… I hate when my dog unexpectedly jumps off the couch and tries to bite the monitor…… Good boy  I heard you….but couldn’t resist |
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Post by AudioHTIT on Nov 3, 2022 14:50:41 GMT -5
Sorry ... I think you both missed my subtle attempt at humor 😊 ... Two Barking  Sometimes home theater is too realistic… I hate when my dog unexpectedly jumps off the couch and tries to bite the monitor…… Good boy What can cause tube arcing: 1. Gas in the tube. (That can happen due to air leaking in through a crack or bad seal.) (It can also happen if poor quality metal surfaces inside release trace amounts of gases.) (It can also happen if certain metal surfaces get way too hot (they may then release gases that they otherwise wouldn't)). (The tube could simply have a weak vacuum due to poor manufacturing.) 2. Too high a plate voltage on the tube. (Some designers run their tubes really close to their safe voltage limit to squeeze a few more watts out of them.) (Some similar tubes, or even the same tube number from a different vendor, may have slightly different limits.) (The plate supplies in tube amps usually are not regulated, so they can drift if the line voltage changes, or if the current you draw from them changes.) (UNAUTHORIZED MODIFICATIONS. For example, if you substitute solid state rectifiers for a tube rectifier, it will usually raise the plate voltage significantly.) 3. A mechanical flaw or shipping damage. (Two parts got bent and are too close together.) (Or an insulator/spacer has become bent, loose, or cracked.) (With poor quality tubes you could even have small metal scraps or filings floating around inside.) |
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Post by pedrocols on Nov 3, 2022 21:27:15 GMT -5
I would think with the technology being as old and obsolete as it is, that things like quality, control, and availability would be wreaking havoc on replacement tubes Old and obsolete just like your speakers. |
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Post by garbulky on Nov 4, 2022 0:54:51 GMT -5
Oh boy. You guys...
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Post by 405x5 on Nov 4, 2022 7:22:58 GMT -5
Sorry ... I think you both missed my subtle attempt at humor 😊 ... Two Barking View AttachmentSometimes home theater is too realistic… I hate when my dog unexpectedly jumps off the couch and tries to bite the monitor…… Good boy What can cause tube arcing: 1. Gas in the tube. (That can happen due to air leaking in through a crack or bad seal.) (It can also happen if poor quality metal surfaces inside release trace amounts of gases.) (It can also happen if certain metal surfaces get way too hot (they may then release gases that they otherwise wouldn't)). (The tube could simply have a weak vacuum due to poor manufacturing.) 2. Too high a plate voltage on the tube. (Some designers run their tubes really close to their safe voltage limit to squeeze a few more watts out of them.) (Some similar tubes, or even the same tube number from a different vendor, may have slightly different limits.) (The plate supplies in tube amps usually are not regulated, so they can drift if the line voltage changes, or if the current you draw from them changes.) (UNAUTHORIZED MODIFICATIONS. For example, if you substitute solid state rectifiers for a tube rectifier, it will usually raise the plate voltage significantly.) 3. A mechanical flaw or shipping damage. (Two parts got bent and are too close together.) (Or an insulator/spacer has become bent, loose, or cracked.) (With poor quality tubes you could even have small metal scraps or filings floating around inside.) Admittedly… I’m still missing it (but I like the picture!) |
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KeithL
Administrator
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Post by KeithL on Nov 4, 2022 8:46:44 GMT -5
Tube arcing... I just love vintage tech... (mercury vapor arc rectifier)    |
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