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Good Evening,
Last week I ordered a quad of Gold Lion Genalax KT88. They came this afternoon. I put them into my Grant Fidelity A-348 and biased them to .48. Within 5 minutes I had one tube get bright red. It was red for about 3 seconds. A small burn mark, the size of a dime resulted. I quickly shut off the unit. I then let it cool for a few minutes. I then turned the bias low and turned the unit back on. I started with .4 and in 20 min increments moved the bias up to .48. It has been on for four hours now and it seems fine. Sounds fine. I know there is a break-in period. But I mean that channel, the right, does not sound different than the left. Nothing inside lookes burned or cracked. Do you think there is any damage to the tube?
I await your reply and thoughts.
R.E.B.
Follow Ups:
A lot of the tubes from Russia seem to cross the water before having been burned in sufficiently. In the small 9 pin tube varieties, I and others have observed a 50-100 hour period where a given Russian tube will slowly increase its current until it gets pretty close to specification. In your case, you may have had one KT88 that was particularly green, and once it woke up from some use, it started drawing proper current.
It's best with a new set of Russian outputs to run the tubes at a very cool bias point for a few days just to be sure, or buy them from McShane, as I get the impression that he runs them in pretty well.
....... as the bias window on any amplifier should never be so wide as to do damage to a tube. Better get it checked out fast.
"as the bias window on any amplifier should never be so wide as to do damage to a tube."
Actually, a too narrow adjustment range causes more trouble (of a different type). Keep in mind that current variation from tube to tube of the same type/brand/etc. will be over 100%. So a wide range of adjustment is needed.
The best solution is to remember to turn the bias WAY down, down near the lowest current position - then install the new tubes and bring the bias UP to the current spec. That way the bias you had on the older more heavily worn tubes won't be there to allow the new tubes to go over current.
Red plate for i minute or so won't damage the tube.
Go out and smoke a joint. maybe
go out for dinner. definately
Bitch getting good tubes now a days
Good luck
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