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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Carvin X50B tube amp
Amp seems to work perfectly well, being repaired for minor problem, no
succeptibility to microphony or tinging distortion. Testing the 2x EL34, gains are good and matched but after a minute on heated C/H insulation check, the resistance gradually decreases to 1M for one and 0.5M for the other. What problems will this lead to if continued use, and how quickly ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Carvin X50B tube amp
On Feb 25, 7:33*am, "N Cook" wrote:
Amp seems to work perfectly well, being repaired for minor problem, no succeptibility to microphony or tinging distortion. *Testing the 2x EL34, gains are good and matched but after a minute on heated C/H insulation check, the resistance gradually decreases to 1M for one and 0.5M for the other. What problems will this lead to if continued use, and how quickly ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list onhttp://home..graffiti.net/diverse:graffiti.net/ It means that the tubes are not precisely matched. Sadly, "matching" tubes these days is typically based only on "gain" and done for a quick claim to inflate prices. No problems if each tube has an individual bias adjustment, and you watch over it. Even if they are biased together and that bias is attended-to, there should be no problems. How many hours on these tubes and are they driven to extremes or not? What are you testing with? http://hereford.ampr.org/Tube4.php?tube=6CA7 Peter Wieck Wyncote, PA |
#3
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Carvin X50B tube amp
Peter Wieck wrote in message
... On Feb 25, 7:33 am, "N Cook" wrote: Amp seems to work perfectly well, being repaired for minor problem, no succeptibility to microphony or tinging distortion. Testing the 2x EL34, gains are good and matched but after a minute on heated C/H insulation check, the resistance gradually decreases to 1M for one and 0.5M for the other. What problems will this lead to if continued use, and how quickly ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse:graffiti.net/ It means that the tubes are not precisely matched. Sadly, "matching" tubes these days is typically based only on "gain" and done for a quick claim to inflate prices. No problems if each tube has an individual bias adjustment, and you watch over it. Even if they are biased together and that bias is attended-to, there should be no problems. How many hours on these tubes and are they driven to extremes or not? What are you testing with? http://hereford.ampr.org/Tube4.php?tube=6CA7 Peter Wieck Wyncote, PA Unknown age, matched GT tubes, no date on tubes used by a pub rock band tested on Avo CT160 |
#4
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Carvin X50B tube amp
On Feb 25, 9:38*am, "N Cook" wrote:
Unknown age, matched GT tubes, no date on tubes used by a pub rock band tested on Avo CT160 OK... Attend to the bias to the extent possible, and suggest that they travel with a spare set of tubes. If you have a new 6CA7/EL34 to test against, try that just to make sure you are not too far off. At least you are using one of the very few testers that actually gives reliable information. Peter Wieck Wyncote, PA |
#5
Posted to rec.antiques.radio+phono,sci.electronics.repair
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Carvin X50B tube amp
Peter Wieck wrote in message
... On Feb 25, 9:38 am, "N Cook" wrote: Unknown age, matched GT tubes, no date on tubes used by a pub rock band tested on Avo CT160 OK... Attend to the bias to the extent possible, and suggest that they travel with a spare set of tubes. If you have a new 6CA7/EL34 to test against, try that just to make sure you are not too far off. At least you are using one of the very few testers that actually gives reliable information. Peter Wieck Wyncote, PA This one was used by REME Wing Hebrides in 1984 |
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