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Rock-ola 1448 sound problem fixed....but HOW!!??
Hi group,
I've written before....I am not electromnically educated (this is why I write the group for help/expertise). My Rock-ola 1448 has been experiencing some "muddied" sounding sound recently. I had recently switched volume controls, to "make-up" a new one with a new pot from Vern Tisdale". When I substituted the original pot/volume control, the sound became "muddy" sounding. I tried to fix it today, armed with everything EXCEPT a new nolume control pot/wired harness. I tried a new needle (with no success). I then checked tubes with my reliable tube checker. One 6L6 (out of two) showed BAD (not weak; bad!). Also one 6SN7 tube likewise showed BAD (not weak; but BAD again!). As I did not have additional tubes with me, all I could think to do was switch each bad tube with the corresponding good tube's socket (as there were two of each tube in question). Lo and behold....the sound was no longer "muddy". It actually sounded GOOD! Not understanding electronics (like a LOT of you do!), I wondered how this could happen!? If a tube is bad (and two WERE!), then how can switching the tube sockets of each tube suddenly make a the sound come out GOOD! I really don't understand how (maybe I don't WANT to understand how....but REALLY I do/even if it is "above my head" electronically speaking). I really don't want to get "yelled at" by Bill, Paul, or even Robin, by asking them. If my tube checker is accurate, and showed that each of the two tubes (6L6 and 6SN7) were BAD, then how can simply switching the tubes in the tube sockets make it sound great! I did re-build/re-cap the amplifier several years ago. Please, since I am electronically "illiterate", shed some light on this for me! I don't feel I'm asking for too much; just an unknowing one's undersytanding of (simple?!) electronics. Trust me; I can't find this out by reading a book (or a schematic/manual; even if you can). Thanks, Rob |
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#2
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Rock-ola 1448 sound problem fixed....but HOW!!??
I don'tr put much trust in tube checkers. The real way to check is
substitude a known good tube. Many tube testers, especially drug store types read the tubes as bad or weak to sell tubes. I think you had a dirty tube socket and moving the tubes around scrapped some of the corrosion off. Charlie |
#3
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Rock-ola 1448 sound problem fixed....but HOW!!??
I have Heathkit, B & K, and Eico tube testers. Generally if a tube
tests bad or weak on all 3 testers I consider it bad tube. You certainly could have had tarnished pins in the tube sockets since that's an old amplifier. |
#4
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Rock-ola 1448 sound problem fixed....but HOW!!??
Thanks Ken......and you too, Charlie. It sounds like each of your
answers make a lot of sense. The tube checker I have is a small compact model that does a large variety of tube sizes....a Mercury, model 1101. I used to use a Hickock (model 600?), but it quit working a number of years ago. I don't know what went wrong with it, but it quit giving ANY reading for certain #s of tubes, and I finally got frustrated enough to give up on it. I sure wish I could find someone to troubleshoot it for me. The idea of trying one tube in 2 or 3 different tube testers does sound like a great way to go! I guess the interesting thing to find out with the 1448 is what will happen if I switch the two tubes around back the way they were (both the 6L6 and the 6SN7) and see if the sound continues to be great, or if it reverts back to the "muddy" sound. I may try that tomorrow night when I go back for a Sunday visit. Thanks again you guys....you're the best! Rob I have Heathkit, B & K, and Eico tube testers. Generally if a tube tests bad or weak on all 3 testers I consider it bad tube. You certainly could have had tarnished pins in the tube sockets since that's an old amplifier. |
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