Rich says:
>>Seeing the tube is 18 years old and who knows where it came from I think
it >>could be dying a normal death, hi hi.
>I have an 8163/3-400Z that was mfg in 1967 and it still gives full
>output. The best way to test emission is to temporarily increase
>filament potential approx 1/2V. . If the output increases, the end is
>near.
I have a 6L6G mfd in 1935, and it still has full output. But in Kevin's
case, it could well be the tube is dying. Rich's idea will show if the
emission is going. If it is, then you could try 'rejuvenating' the filament
- you've nothing to lose. The usual method is 50% overvoltage on the
filament WITH NO OTHER VOLTAGES applied for 20 or 30 seconds, and then run
at +20% overvoltage for a minute or two, and +10% for 30 minutes. Some
people use different times, and there's no guarantee. But especially if the
tube hasn't had a red plate (so that there could be some gas in it), then
flashing the filament to get a fresh layer of thorium up to the surface
could get a few more years out of it. As I say, you've nothing to
lose....but it's probably worthwhile getting a new tube first.
By the way, make sure the tube is upright, because if it isn't, the
increased filament temperature could lead to sag and welding of filament and
grid.
73
Peter G3RZP
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