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Alan Douglas
 
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Hi,

I have one Mullard EL34 tube. I test it on my HICKOK 539B tester. I
turn the tester power on after 1-2 minutes the micromhos meter is read
on 5600. But test after power on approximately 6-7 minutes the
micromhos meter indicator is reverse and turn the BIAS VOLTS VR is no
function. I test other EL34 tubes have no any problem on the 539B
tester. Does the Mullard el34 or the tester have any problem ?


Sounds as if your EL34 has grid emission, and it takes a few
minutes for the grid to heat up. It is contaminated with material
from the cathode.

Alan