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Post subject: HELP PLEASE!! My '65 Twin Reissue distorts like mad above 3!
Posted: Fri Apr 18, 2008 3:35 pm
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I was playing my '65 Twin Reissue a couple of days ago with the volume at about 1.5. I unplugged a stompbox in the signal chain without putting the amp on standby (I do this once in a while without thinking) and it made the usual popping sound. I don't know if the stompbox incident was the culprit or whether it was just coincidence but when I turned the amp up to 3, I got major distortion, and it just got worse if I turned the volume up any higher. It used to be that I could turn it up to 10 and it would sound as clean as country water. I don't use this amp that much, got it in 2005. It's the 40th anniversary edition with the Eminence speakers that came out in 2003, but mine was new when I bought it. I doubt that I have 20 hours on it. The speakers look fine physically, but sound like the old 'tear the speakers to get distortion' trick we used on our cheap amps in the 60's. I checked out the tubes to see if any were loose (they weren't) or if any didn't glow. The tubes appear o.k. physically. I am a near zero when it comes to electronics. If anyone has some ideas of simple things I could check before I take it to a technician, I would be most appreciative. I don't know what happens electronically when someone "blows" their amp. My sounds blown. Help me, please!!! I hate to beg but I love my amps, so .... please!


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Posted: Tue Apr 22, 2008 11:10 am
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The unplugging of the pedal didn't have anything to do with it. Probably a bad tube. Do the pencil test and tap each preamp tube and see if one make a loud noise when you tap it. If it does replace that tube. You could also have a cracked solder joint but I doubt it with the little use yours has seen. Let us know after you do the pencil test.


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Post subject: I did the pencil test...
Posted: Tue Apr 22, 2008 6:13 pm
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Thanks, StratTone, for the great suggestion. I did the pencil test, but no tubes made any noise. I could hear my tapping coming through the amp, but there were no odd noises. One preamp tube did not light up at all, and when I tapped it with a pencil, no sound came through the amp as it did with all the other preamp tubes. Every tube was glowing except this one preamp tube. Is that an indication that it needs replacement? I would think so. It seems logical, but then I am not very knowledgeable when it comes to the inner workings of tube amps. Can I buy just a single 12AX7 tube, or do they have to be replaced in matched pairs or quads like the output tubes? And if so, which ones need to be matched and replaced? This would be an easy fix. Taking my amp to a service depot would be tough, as I am disabled and can't drive, or even carry my amp. I would have to rely on the kindness of relative strangers, which makes me a bit uncomfortable.


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Post subject: Addendum
Posted: Wed Apr 23, 2008 8:23 am
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I forgot to mention that the tube that didn't glow was the one next to the output tubes. Initially I thought it was glowing, but it was merely reflection from the adjacent output tube.


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Posted: Fri Apr 25, 2008 9:37 am
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The tube you are referring to is the Phase Inverter tube. A lot of people like to have a balanced triode PI in there amp. It should be glowing for sure. I would highly reccomend buying tubes from dougstubes.com I can't begin to say the importance of getting a good properly tested tube. You dont' want to spend good money on a brand new tube that tests low. Doug tests all his tubes.


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