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In Reply to: RE: El 84 only lights half way posted by lesleymorley@yahoo.com on March 04, 2014 at 05:53:10
Hello!
If you're really not sure, fire them up, take some photos of the two tubes and the trouble spot, and post them.
It may just be the heater is little shorter, more "hidden" in its cathode. I think "technically" as long as the cathode is more or less uniformly glowing, heater length should not matter. If you see it's unevenly heated towards the top, I would be a little miffed. If it isn't, then no worries. The fact they work operate as expected is another indication that things should be fine.
There's been quite a lot of buzz about this issue lately: heaters that don't seem long enough, or are too long and nearly pop out the top of the cathode. Many power tubes I've bought lately have slight variations in heater wire length, including JJ 6CA7's and KT77's, and even New Sensor's Gold Lion KT77's.
Maybe someone can chime on this random question: longer heater, or an uneven thoriated tungsten coating, could mean more draw right?
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May your tubes be lively and long-lasting. Holy be thy heater.
Follow Ups:
Sondek nailed it, the heater just doesn't stick out of the cathode sleeve far enough at the top to be visible. Completely normal.
Thanks to all of you. Now I will enjoy my amp without any concern.
Check the plate voltages and idle bias current of the EL84's. Bet that they are ok, but if not... you'd spot the bad tube(s) or socket(s).
Edits: 03/04/14
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