BBZink Posted May 24, 2016 Share Posted May 24, 2016 Good Day All, just bought in garage sale, a fisher kx-90 integrated amp, when i start the amp, all 4 el84 glow and only 2/5 12ax7 glow, but 3/5 12ax7 don't(starting from left side, facing the amp). I search internet and found, that it was a fisher kit from 1965, but not able to find manual or schematic! Anyone could help me? finding that? from what i have read, it should be sounding great, but for now, only a huge hum, from it Best regards All Quote Link to comment Share on other sites More sharing options...
BBZink Posted May 24, 2016 Author Share Posted May 24, 2016 From my research, it could be the clone of X-100-A, from fisher to be sell as a kit KX-90? anyone could confirm? regards Quote Link to comment Share on other sites More sharing options...
NOSValves Posted May 24, 2016 Share Posted May 24, 2016 (edited) The voltage that lights those 3 12AX7's is derived from the cathodes of the 4 output tubes. So the problem is not actually in those 3 12AX7's. For some reason those output tubes are not conducting. Because a tube is lighting does not mean its working what lights in a tube is the heater. The tube can not work without the heater lighting but being lit does not mean the tube is operational. You can get the service manual here http://www.fisherconsoles.com/non%20console%20manuals/fisher%20x100-3%20sm.pdf Oh wait I misspoke a bit. One of the 12AX7's could possibly be the problem if one has a heater winding that is shorted open. To check all 3 12AX7's plug them into the sockets where the two 12AX7's are now lighting and see if all 3 will light. If they light then the problem is elsewhere. It could even be that for some reason the amplifier has no high voltage B+ present. But usually when something goes wrong with the high voltage B+ the amp will blow fuses. Edited May 24, 2016 by NOSValves 1 Quote Link to comment Share on other sites More sharing options...
BBZink Posted May 28, 2016 Author Share Posted May 28, 2016 Many thanks, amp is at technician with manual, will probably have it back in a week or two, look foward to hear it on my belle. For now, i am listening my dynaco st-70! but preamp tube aren't available any more, i wish my preamp tube will last on this one... Quote Link to comment Share on other sites More sharing options...
BBZink Posted July 12, 2016 Author Share Posted July 12, 2016 The voltage that lights those 3 12AX7's is derived from the cathodes of the 4 output tubes. So the problem is not actually in those 3 12AX7's. For some reason those output tubes are not conducting. Because a tube is lighting does not mean its working what lights in a tube is the heater. The tube can not work without the heater lighting but being lit does not mean the tube is operational. You can get the service manual here http://www.fisherconsoles.com/non%20console%20manuals/fisher%20x100-3%20sm.pdf Oh wait I misspoke a bit. One of the 12AX7's could possibly be the problem if one has a heater winding that is shorted open. To check all 3 12AX7's plug them into the sockets where the two 12AX7's are now lighting and see if all 3 will light. If they light then the problem is elsewhere. It could even be that for some reason the amplifier has no high voltage B+ present. But usually when something goes wrong with the high voltage B+ the amp will blow fuses. Amp works great, for the last month, thank you all, it has a good sound, but not quite, as my old 1957 harman kardon. But impressing powerful with my Belle! 1 Quote Link to comment Share on other sites More sharing options...
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