CaptnBob Posted July 10, 2011 Share Posted July 10, 2011 What tubes are supposed to be in this amp? The sticker on the bottom says 4 - 7591, 4 - 12AX7, and 2 - 6GH8. The Scott website agrees, except subbing 6U8s or 7199s for the 6GH8s. The tubes themselves are no help, as the lettering is long gone. I tried testing them as 6GH8s, but they didn't seem happy early on in the Hickox tube tester, so I pulled the plug. Any ideas would be appreciated. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted July 10, 2011 Share Posted July 10, 2011 If testing them as 6GH8s (6U8s have the same pinout) didn't work, try testing them as 7199s. The latter have a different pinout from the former. If you have a copy of the schematic, try to correlate the pinout on the bottom of the tube socket with the tube types and you should have your answer (i.e. look at the components connected to each pin and then reference the schematic to see which is the plate, grid, cathode, etc.). Quote Link to comment Share on other sites More sharing options...
CaptnBob Posted July 10, 2011 Author Share Posted July 10, 2011 That would add - the meter on the tube tester started burying itself to the left. Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted July 15, 2011 Share Posted July 15, 2011 Bob, I belive the hot pins are reversed, so you may be looking at 7199s. I'll be in Alton Saturday afternoon, so I'll call you when I finish up picking the Citation V up at Mark's. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 17, 2011 Share Posted July 17, 2011 I've seen a meter go the wrong direction many times on the Hickok when the tubes pins are not making proper contact so I would not jump to the conclusion that the tubes are not 6GH8. I've never seen a Scott amp that had the wrong sticker on it's bottom cover. I guess it could happen though. The 299C was made with both the 6GH8/6U8 and 7199 as driver/phase splitters. I'd try cleaning the tube pins with contact cleaning and a brass brush. also the metal contact in your tubes testers socket. Then try testing the tubes as 6GH8 and then if that does not work 7199. If the amp is wired for either tube only the proper tube type will play music. The wrong tube installed will result in zero music and added noise. Quote Link to comment Share on other sites More sharing options...
CaptnBob Posted July 18, 2011 Author Share Posted July 18, 2011 Thank you kindly, sir. Bob A. Quote Link to comment Share on other sites More sharing options...
rongon Posted July 21, 2011 Share Posted July 21, 2011 There's always the possibility that a previous owner modified the amp to use 7199 instead of 6U8/6GH8A. Does your tube tester have the 7199 info on its reel? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 21, 2011 Share Posted July 21, 2011 usually folks do the reverse since 7199 are so pricey so that is most likely not the case. But yea just never know. Quote Link to comment Share on other sites More sharing options...
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