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Old 8th March 2013, 04:20 PM   #121
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The Workrite 4000 has 4 x 810 tubes. The arcing was caused by the wrong application, I was trying to glue very thin strips of bamboo.
I understand that RF gluing is not the same as induction heating but I'm guessing the interference is similar?
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Old 8th March 2013, 04:33 PM   #122
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by radiosmuck View Post
Unpaved roads in the UK in the 50's? What part of Fairyland are you from?
I think he means cobbled, rather than 'unpaved'.
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Old 8th March 2013, 09:48 PM   #123
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It's essentially the same type of idea... slightly different application and different "business end" of the unit...

4 x 810 is a boat load of tubes... it doesn't matter what the arcing was caused by, just that IF and when it does happen, major interference is created.
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Old 9th March 2013, 12:07 PM   #124
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Originally Posted by DF96 View Post
As precisely the same problem appears to be solved by the getter during manufacture, I assume the getter can mop up nitrogen OK. Metals do form nitrides! Argon maybe not.
You are absolutely right. I was thinking room temperature, but at high temperatures barium bonds with nitrogen to form a stable nitride.
So we can conclude that during storage, the barium getter will catch oxigen, but nitrogen gas remains present untill the getter gets hot enough to initiate the reaction.
This explains the improvement that MJ found in his baking experiments.

The question remains however, if using the valves in a regular circuit would not have given the same results.
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Old 9th March 2013, 02:41 PM   #125
DF96 is offline DF96  England
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If there is a lot of gas then there is a risk of thermal runaway or cathode damage under normal operation. Baking avoids this. Never tried it myself, but I can see that it might sometimes be useful.
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Old 12th March 2013, 11:29 AM   #126
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Thermal runaway, ok. But how often does this occur?
Except for '80s chinese power valves I have not seen valves running away.
I do have noisy old valves. Perhaps due to high gas that the getter can't absorb under normal operating conditions. Baking might improve those.
Preventive baking (doing so without testing for gas first), for me is overdoing it a bit. Not to mention introducing thermal stress that could have been avoided.
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Old 12th March 2013, 12:45 PM   #127
DF96 is offline DF96  England
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Thermal runaway is often seen in smaller older power valves when they get gassy. EL41 often end their lives in this way.
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Old 12th March 2013, 01:48 PM   #128
TheGimp is offline TheGimp  United States
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I had a couple of 6P1P-EVs go this way. I have not experienced any since I started baking them before powering them up (20 tubes).
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Old 12th March 2013, 04:29 PM   #129
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Quote:
Originally Posted by DF96 View Post
Thermal runaway is often seen in smaller older power valves when they get gassy. EL41 often end their lives in this way.
Good to know: I have collected quite a few years ago.
When I finally get to using them I will test and monitor them closely
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Old 12th March 2013, 10:32 PM   #130
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Quote:
Originally Posted by Parafeed813 View Post
Thermal runaway, ok. But how often does this occur?
Except for '80s chinese power valves I have not seen valves running away.
I do have noisy old valves. Perhaps due to high gas that the getter can't absorb under normal operating conditions. Baking might improve those.
Preventive baking (doing so without testing for gas first), for me is overdoing it a bit. Not to mention introducing thermal stress that could have been avoided.
Sorry my ignorance, but how is this gas test for tubes?? (small and power tubes).
It will be quite useful to me.
Thanks
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