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In Reply to: Amplifier problem posted by tubers on February 19, 2007 at 21:33:06:
It sounds like either the bias is set incorrectly or some of the tubes are drawing grid current (gassy perhaps). Check the bias and attempt to adjust it. If you cannot set the bias have the tubes checked.
Follow Ups:
Thanks for advice!The amp has an auto-bias circuit, so I cannot check it. Strange thing is when I put other quads (expensive GEC KT-88), one of them becomes red-hot in 3-5 minutes, and in different sockets at that! I will try to borrow a quad of Sovtek KT-88 tubes from a friend and will see how they behave.
It sounds like you have a bad tube, especially since only one tube gets red hot and that same tube does this no matter which socket you put it in.As for the cool down time; Perhaps the resistor problem that was repaired corrected a low bias condition and the amp is working correctly now? Since there is no provisions to measure/set the bias take the amp back to the shop and have the technician check the bias to be sure it is working properly.
Tubers
When you put the quad gec kt88s in,is it only one that gets hot in any socket?
Yes, Michael, only one.
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