oscarsear Posted December 3, 2004 Share Posted December 3, 2004 Curious about my recent tube experiences. I've had 3 failures in new and young tubes. A KT-88, KT-90 and a rectifier tube 5U4G. I'm using an integrated SLI-80 Cary amp and all failures have occured in the left channel. 2 of these failures were instantaneous meaning they crashed and burned on their initial outing (actually it maybe that the bad rectifier tube fried the KT-90). Once refitted everything works well. All tubes were replaced gratis from my source. Is this a component problem....a quirk of these vintage make tubes and therefore 2 B expected.....or a problem with my supplier??? Appreciate the input. Quote Link to comment Share on other sites More sharing options...
dodger Posted December 3, 2004 Share Posted December 3, 2004 It could be one of several things. Too much current. If the tubes were all ordered at once and arrived in the same box, it may have been dropped how they are stored, I'm sure there are other factors such as bias and others. dodger Quote Link to comment Share on other sites More sharing options...
oscarsear Posted December 3, 2004 Author Share Posted December 3, 2004 I know the bad rectifier tube allowed too much current through the line. I watched it on my multimeter as the fuse exploded. I do pay particular attention to my bias consistency checking very frequently with any tube change. I use KT-88's for classical and the 90s' for jazz, in particular. Also I keep my tubes clean, grease free and cool. Still I'm wondering about the high failure rate because I've not heard this from others. My supplier suggests that I'm less than lucky....but I don't believe in reading the stars. Thnx Dodger Quote Link to comment Share on other sites More sharing options...
NOSValves Posted December 3, 2004 Share Posted December 3, 2004 As far as output tubes are concerns defective or low quality tubes will usually show up when you biasing the amps. If the measurement is somewhat stable with no signal being pumped into the amp then they are most likely fine (some preamps can cause instability so check it with the preamp off). Many homes have wildly varying wall voltage from one time of the day to another so if the bias drifts up and down on all the tubes relatively consistent at different times of the day don't worry about it but if one tube seems to always need bias changes compared to the rest its suspect. Tubes sockets can be a source of trouble if you constantly roll tubes especially with output tubes of various brands. The diameter of the actual tube pins from one manufacturer to next varies so one tube type might stretch the connections in the sockets so other tubes with smaller pins can get no connection or intermittent connection. it should take some force to pull octal tubes out of the socket if it doesn't get a dental pick type tool and tension those tube sockets. The 5U4 is a instant on rectifier just like SS rectifiers so its not kind to the rest of the tubes in the amp. It can easily manifest any weak points. Craig Quote Link to comment Share on other sites More sharing options...
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