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Killing my tubes softly

4.246.204.158

Posted by Wellsmith on August 13, 2006 at 16:50:00

I believe I committed negligent tub-o-cide on a quad of winged 'c' 6550's. I do not have a tube tester, but when I try to bias them, they run away from me like most girls did in the 6th grade.

I am able to bias several sets of NOS tubes in the same Mark III's without problem, but these just run on up to over 1.0v (.5v bias standard), and are unaffected by changes in the resister values in the bias circuit (all the way up to 100K). All the other tube sets respond accordingly to the resister changes, but the winged 'c' set have never come below .9vdc.

I should mention that I had voltage across the plates of 525 volts during testing of the regulated power supply when a regulator failed. Did I kill my tube set? I keep hoping that these just had an unusually high transconductance, and needed a bias supply adjustment resister. This set of tubes has caused me to start drinking again....anything but Russian Vodka. High voltage and a drunken stuper may be the fitting end for both me and tubes. On the other hand, I have a new set of Tungsols from Ned on the way. Perhaps these will bias correctly. In the meantime, I still have my JC Penny SS console that always works, but unfortunately, sounds like a leaf blower.

Can anyone tell me if a particular brand of tube is KNOWN to have especially high transconductance that causes biasing problems??

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