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?
I understand that RF gluing is not the same as induction heating but I'm guessing the interference is similar?
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.
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.
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.
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.
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.
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.
Thermal runaway is often seen in smaller older power valves when they get gassy. EL41 often end their lives in this way.
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).
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
Sorry my ignorance, but how is this gas test for tubes?? (small and power tubes).
It will be quite useful to me.
Thanks
Some testers can do a gas test. Essentially it measures grid current, perhaps by determining the voltage drop across a large resistance.
if you have a sensitive DMM with uA range I don't see why not, the gas test on AVO VCM is 100uA ammeter in series with control grid, with the tube under test biased for normal operation
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Thanks boys for help.
I afraid it is impossible to do this gas test with the tube outside the amp.
I afraid it is impossible to do this gas test with the tube outside the amp.
Just clip a couple of test leads across your grid-leak resistor and measure the voltage, if any. If you're drawing grid current, you will see a voltage produced across this resistor.
The current is I=E/R - simple. 🙂
To do a gas test the cathode must be hot and the anode must be positive so that electrons can create some ions, which then get seen as grid current.
Sorry to join the conversation so late, but...
I, too, had problems with 6Н1П-EB (among others), and I used to bake NOS tubes (a la Morgan Jones), but have found an equally effective (for IHT's anyway) method that takes a good deal less effort and presents no risk to bakelite bases:
By running the heater off of a current-regulated (benchtop lab) supply with no B+, the same improvement that Morgan describes in his article can be had overnight while I sleep.
The current-limiting causes the filament to come up very slowly - (it takes about 100-200 seconds for a 6Н6П, for example, to reach 6.3V @ .75A) - and then the heat from the filament does the baking just as well as the oven used to.
The by-product, of course, is that in the morning, I have an already-warmed-up tube ready for testing - I ramp-up B+ to the plate (over about 15 seconds), check grid leak, then read cathode currents at a couple different bias volts for matching/QC purposes at this point.
I take two senile 6C33C-B tubes to baking, both are Ulianov SET1983 OTK 11.
V1 had no more vacuum, a glass/metal pin top nipple broke and its structural pins are non aligned probably due a huge G force in a jet.
Getter had a subtle blow away gray area near the top due air entrance. Plate is very clean. no sign of dust getter.
V2 is factory sealed yet, seems good vacuum, very few signs of dust getter on the plate.
I put a bread to baking in the gas stove at minimum temperature= 180ºC and also include these two tubes.
They cooked for two hours, after it both tubes had few getter on top, the plate seems more clear, with less black dust getter.
After a week or so, I baking both tubes again and the top getter decreased again, seems very little now in both tubes, almost vanished, the top glass is near transparent in both tubes.
Seems to me 180ºC is too hot for thiese tubes, I would suggest 100ºC for one or two hours for the first time.
V1 had no more vacuum, a glass/metal pin top nipple broke and its structural pins are non aligned probably due a huge G force in a jet.
Getter had a subtle blow away gray area near the top due air entrance. Plate is very clean. no sign of dust getter.
V2 is factory sealed yet, seems good vacuum, very few signs of dust getter on the plate.
I put a bread to baking in the gas stove at minimum temperature= 180ºC and also include these two tubes.
They cooked for two hours, after it both tubes had few getter on top, the plate seems more clear, with less black dust getter.
After a week or so, I baking both tubes again and the top getter decreased again, seems very little now in both tubes, almost vanished, the top glass is near transparent in both tubes.
Seems to me 180ºC is too hot for thiese tubes, I would suggest 100ºC for one or two hours for the first time.
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digitrax - if you apply insulation over the glass region that has the getter material, then the getter should reach a higher temperature than if left uninsulated, and hence improve the gettering process for the same time and/or heater power level.