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I have some gassy GEC KT66 tubes.
I have heard that sometimes it helps to raise the voltage after plugging them into a tube tester. Is this true, and if so, how much and how long?\\
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I agree with everything mentioned, but I have a warning:
I once left a 6L6GC in my TV7/DU overnight. The next day I found the fuse lamp blown and a shorted primary on the power transformer.
I suspect the power trans is not rated for 100% duty cycle.
Peace,
DrRick
When I got them,one of them had some silver getter flashing on top so I tested them in the Hickok 539b and they tested fine..I then tested them in the Heath TT-1 and they also tested well but showed grid leakage on both tubes...I told the seller and I didn't want any money back or anything, so he sent me three NOS/NIB 12BH7 black plates for leaving him good FB.They play and sound fine and now the grid leakage had disappeared..The one still has that tiny flashing on top but they perform flawlessly..Apparently he sold the tubes once before and they came back and that's probably why he sold them so cheap.
Just leave the tubes in a tube tested running just the filaments and they will work out the leakage many times.You can also put them in an amp as long as they aren't shorted and work the gas out that way as well.
Honest amplification is better than excessive 2nd order distortion anytime.
I've degassed many tubes now just be leaving them in the tube tester at idle (heater on, normal voltage) for several hours. As the getter splat gets hot it slowly adsorbs whatever residual gas is in there.
Also, if you have newly acquired old tubes that test low but look good, you can often "wake them up" by leaving them on the tube tester with the heater on. This can take between 1 hour and a couple of days, and doesn’t always work. If a tube looks shot and tests low, I let it go, but if it looks good and test low I try the "wake up" procedure.
I have no idea what's going on in the tube that would cause temporary low emission, but respond to heat over a period of time. Does gas settle on the cathode and need to be baked off? I've seen this "wake-up" effect many times no on tubes that haven't been useRE: I bought a pair of KT66 Brit Genelex clear glass for 50 dollars BINd in decades. It doesn't always work but it's worth a shot on all but the least valuable tubes.
I have no experience with raised heater voltage but you could try baking in an oven , I have had limited success with this . Alternatively you could try running the tube heaters only on the tester overnight . Sometimes I have found power tubes to test as less gassy on lower G2 voltages , then retested after a few hours soak test at normal G2 voltage . YMMV and all that etc etcAl
Edits: 03/31/14
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