Hey All - I've got an '06 Z28 that I'd like to re-tube/tune up. I purchased a VHT Bias unit and went to check the bias of the current set of power tubes (GT's). When I powered on the amp and stand by, I had one tube glow bright white and a loud hum came out of the speaker for about 2-3 seconds, then the fuse blew.
I removed the bias tester, put a new fuse in, and re-installed the power tubes. Now I notice that one of the power tubes does not light up at all when the amp is turned on. I plugged a guitar in and it makes sound just as normal but I'm wondering about that tube. I swapped positions of the power tubes and still the one tube does not glow at all.
Does anyone have any insight as to why this is?
I have a brand new set of matched JJ's ready to go in, but I want to figure this out before I put them in and possibly damaged the new set.
Thanks in advance for any help!
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Well if swapping the tube positions the un-lite tube moves to the next slot then it's a bad tube. If the un-lite tube now lights and the other that was moves doesn't then it's an internal issue. What could have happened that caused that tubes filament to fail is hard to say.
I have has issue with one socket needing to retensioned to get to work...just did it today as a matter of fact...
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Post by premiumplus (Dave) on Mar 25, 2019 17:30:02 GMT -7
I just got an old 1981 Carvin and one of the output tube sockets was so worn that the keyway allowed the tube to be inserted in the wrong orientation. Surprise...the heater didn't work! I re-aligned it and all is well again.
"Tone, tone, tone, tone. Is there a substitute?" -Dr.Z
Those keyways don't wear all that much. The real defect is that some companies use really cheap sockets with a sloppy fit to begin with. The worst I have seen were ceramic, although that doesn't mean ALL ceramics are bad. They just vary more from part to part. Also the way you remove tubes determines how quickly they become loose. I've seen it demonstrated and recommended that you wiggle the tube in a circular motion when pulling them out. That, with an excessive movement, is the worst thing you can do. It is best to just SLIGHTLY wiggle them from side to side as you pull. Also make sure the pins are straight when inserting them. A pin straightener tool is handy for this. It will eliminate the socket being used as a "straightener tool" which will deform it.
Loose pins usually come from "tube rolling" which I don't like. Although there are some newer tubes with smaller diameter pins that will require tweaking the socket for a proper fit. What a pain. I might try 2 or 3 different tubes but that is all. If I don't hear a significant improvement by then I go back to what Doc Z originally used.
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