This tube works cold and fails hot. Runs normally for maybe ten minutes and then "just stops passing signal" with no pops or bangs or complaining at all. It just stops. Filament stays lit.
Tube is NOS and failed with a couple hundred hours on it. Perhaps this is a clue? - it operates horizontally and the funny looking getter was near the bottom.
36KD6 Beveridge amp
Tube is NOS and failed with a couple hundred hours on it. Perhaps this is a clue? - it operates horizontally and the funny looking getter was near the bottom.
36KD6 Beveridge amp
I suspect that you have a hairline crack in one of the conductors. As the valve warms up, thermal expansion eventually widens the crack enough to break the circuit. If the crack is inside the valve I doubt that you can do anything, but if it is an external crack or bad solder joint, you may be able to repair it,, if only you could find out where the crack is.
One of those getters looks like it has been exposed to air. The other looks shiny but has a halo around it.
They say that in case of a faulty tube from the factory, the fault happens in those first couple of hundred hours.
After that it's extremely rare that something other than age causes any faults.
They say that in case of a faulty tube from the factory, the fault happens in those first couple of hundred hours.
After that it's extremely rare that something other than age causes any faults.
Usually the getter degrades in this way when the tube glass exceeds the maximum allowable temperature. Airflow may be impeded. Deformation due to excessive temperature may crack the internal solder joints between elements. Internal wires stay close togheter when cold, thermal expansion is enough to open the circuit.
No , getter is reacting with something inside , air ( oxigen ) or other chemical residues . Excessive temperature could be the result of imperfect vacuum .
How many such "deformations" have you seen ? Welds are the last thing to fail because of extra temperature ... Fine grid wires would melt long before and that's game over , tube not working cold or hot
How many such "deformations" have you seen ? Welds are the last thing to fail because of extra temperature ... Fine grid wires would melt long before and that's game over , tube not working cold or hot
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To my knowledge, this type of getter discoloration is due to excess heat, such as guitar tube amps that have been fitted inside a portable rack without proper cooling. The tube may still work fine, but I usually find that it does have reduced emission. I guess that the glass temperature does have a role on the color change, but it may also be outgassing from internal tube elements.
Agree, the tube got hot. Plenty of getter left. When a tube gets too hot, the metals in the electrodes release gases that react with the getter. Those gases are captured in the getter, allowing the tube to continue function correctly. I would suspect that it got hot due to a leaky coupling capacitor or another failure mode in the tubes circuit causing current to run away. Tube is likely still good (enough) for proper operation once the fault is corrected.
Resolder the pins. I have seen this before. It might be helpful to remove the old solder, carefully add some liquid solder flue (for electronics!!), and use fresh solder. I have had to repair tubes before, octal types. For the pins that are not soldered, you have an open and the tube is toast.