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Re-activate getter/save gassy tube
Re-activate getter/save gassy tube
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Old 31st October 2016, 11:08 PM   #1
zyt is offline zyt
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Default Re-activate getter/save gassy tube

I think, I'm not the first person doing this.

with a simple induction heater, the getter can be re-activated to improve the vacuum.

I have tried this to some very gassy tubes, and once there still a little bit mirror left, in most case, the vacuum can be restored.

it also good to heat the getter for a short moment (about 3 seconds), for those NOS tubes before first time heat up the cathode.

before getter re-heat, a lot holes on mirror.

Click the image to open in full size.

during the process, the getter should not go too hot (no more than orange - yellow), otherwise it melt

Click the image to open in full size.

after 5 second heating, the getter mirror become much more thick.
The glowing during (normal circuit) operation is gone.

Click the image to open in full size.

Last edited by jazbo8; 4th November 2016 at 03:40 PM. Reason: spaces
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Old 31st October 2016, 11:50 PM   #2
BinaryMike is offline BinaryMike  United States
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Looks like fun. Tell me more about this "simple induction heater."
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Old 31st October 2016, 11:50 PM   #3
TheGimp is offline TheGimp  United States
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How much power does it take to reactivate the getter?
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Old 1st November 2016, 02:48 AM   #4
ashok is offline ashok
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Re-activate getter/save gassy tube
Zyt, any details of your induction heater so that we could build one ?
Thanks.
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Old 1st November 2016, 03:02 AM   #5
PRR is online now PRR  United States
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> details of your induction heater

Google is your pal.

First page has many links to eBay for coil-things just like in his picture.

They are apparently used to harden steel knives or to melt gold.

It is the same technology the tube factory used to boil the getter-ring.
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Old 1st November 2016, 07:47 AM   #6
zyt is offline zyt
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Hi guys

I use this circuit:
(you do not need to by one, forced air cooling will be sufficient)
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


the critical thing to make this thing work is:

1. choose the right capacitors. I use 4x 22nF 50V NP0 ceramic capacitor in parallel. I have tried various "plastic" film capacitors (MKP etc.), they got very hot and bulged after 5 minutes. any class 2 ceramic capacitors (X7R etc.) also not work well, I have tried 220nF 250V X7R capacitor, again, very very hot, and they cracked after several time use.

2. coil, use some large size wire.

3. increased voltage --> 25V on L2. (standby current is about 0.8A, loaded current is about 2A)

4. find a good fan (hair dryer in cool air) for it.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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Old 1st November 2016, 10:48 AM   #7
hpeter is offline hpeter  Slovakia
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i thought you will heat the getter on glass


ZVS Model Low Voltage Induction Heating Machine High-frequency Heating Machine | eBay
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Old 2nd November 2016, 02:58 AM   #8
Retrovert is offline Retrovert  United States
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Re-activate getter/save gassy tube
First, thank you for posting that simple example of an induction heater.

Here is a question about the effects upon otherwise good tubes.

Over time the heat bakes adsorbed and absorbed gasses out of the metal elements, the mica, and can break up the alkali oxides on the cathode. These ions then cause grid current, among other problems.

Have you tried baking any obviously non-gassy tubes to see if the performance characteristics change when these ions are bound up in the getter material?

A decent tube tester should be able to measure grid current and that is usually an accurate indicator of how many ions are present in the tube.
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Old 2nd November 2016, 09:06 AM   #9
Chris Daly is offline Chris Daly  Australia
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Glad to see the humble clothes peg serving good purpose. Just watch that diode does not touch the heat sink.
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Old 2nd November 2016, 09:38 AM   #10
zyt is offline zyt
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Quote:
Originally Posted by Retrovert View Post
First, thank you for posting that simple example of an induction heater.

Here is a question about the effects upon otherwise good tubes.

Over time the heat bakes adsorbed and absorbed gasses out of the metal elements, the mica, and can break up the alkali oxides on the cathode. These ions then cause grid current, among other problems.
thank you,
the induction heating is only targeted for getter. the plate and grid are not effectively heated to a temperature can release gas. and, mica is not metal.
for the new tubes the grid current can only be generated by the gas ionization in the tube. for heavily used ones, particular high Gm tubes (first grid is very close to cathode and heated by cathode), the first grid had been contaminated by the vaporized cathode coating, make it become "cathode" too, which, obviously results negative grid current.

Quote:
Originally Posted by Retrovert View Post
Have you tried baking any obviously non-gassy tubes to see if the performance characteristics change when these ions are bound up in the getter material?
Yes, for those non-gassy tubes, no change on emission or grid current after getter activation.
note, the induction heating is affect to the getter ring, not the "mirror", because the "mirror" is a layer of amorphous metal, the conductivity is relatively bad.

Quote:
Originally Posted by Retrovert View Post
A decent tube tester should be able to measure grid current and that is usually an accurate indicator of how many ions are present in the tube.
it's difficult to say.
with a current / voltage meter connect to a operating tube between first grid and cathode. for those good tubes, the first grid current is positive ( current flow into grid, negative voltage potential to cathode). gassy tubes, the first grid current is negative ( current flow out grid, positive voltage potential to cathode), this is also the reason of theme-runoff happen to some gassy tubes.
make a comparison between known good tube and test subject is the better way to determine how good / bad it is.
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