12-20-2013, 08:45 AM
Yes, any visible blue or violet glow between the elements is an indication of a gassy rectifier. All vacuum tubes have some residual gas, so it is a matter of degree and whether it affects the tube function.
A rectifier tube is not particularly sensitive to the gas until it gets to the point where it may arc or affects the emission by damage to the cathode. I have a feeling this is why your globe 80 tests low, as its cathode emission has been reduced by the gas ion bombardment over a long period of time.
Its a different story with tubes having control grids, where even a small amount of gas can result in positive grid current, which throws off the bias conditions and can result in excessive plate current.
A rectifier tube is not particularly sensitive to the gas until it gets to the point where it may arc or affects the emission by damage to the cathode. I have a feeling this is why your globe 80 tests low, as its cathode emission has been reduced by the gas ion bombardment over a long period of time.
Its a different story with tubes having control grids, where even a small amount of gas can result in positive grid current, which throws off the bias conditions and can result in excessive plate current.
