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Old 28th August 2012, 11:11 AM   #1
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Default Burn in procedure for NOS necessary?

Dear Folks,

I have some small signal russian NOS tubes ( 6N1P,6N2P,6N6P,6N14P ... ) and would like to use them for small audio projects. In some articles out in the space I read that it is mandatory to "burn-in" alls NOS tubes before use. The reason why to do this is mostly a little bit mystic for me. Someone told: "a certain amount of the gases trapped in its materials is "leached" out into the vacuum of the tube"
The procedure to inspire a tube is fairly complex and take several days. First increase heater voltage over serveral hours/days, grounding grid and no HT voltage. After that do the same with HT voltages and heated tube, grounded grid. At least run the tube a few days/hour well biased but no signal.

I would like to ask you if this is realy necessary or itīs one of the mystic things round about tubes?

Best regards
Karsten
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Old 28th August 2012, 11:15 AM   #2
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I usually burn tubes like those for 24 hours, starting with 3.15V for 6 hours, 5V for 12 and 6.3V for next 6 hours.
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Old 28th August 2012, 11:19 AM   #3
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Hi radiostar,

O.K. you do it but let me ask for the reason. Itīs why "every one" do it, or is there a real physical reason. Or does the manufactor advised this to do before use after long time in stock?

Regards
Karsten
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Old 28th August 2012, 12:46 PM   #4
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Hi!

I don't see a need for a special procedure to burn in tubes. I use many NOS tubes. They do burn in and improve after a while, but I do that in the actual amp.

I would discourage a burn in procedure with heater voltage and no plate voltage for indirectly heated tubes. Many indirectly heated tubes can develop a interface layer when they are operated without plate current unless they are designed for that.

If you insist on a burn in, I would use the nominal heater voltage and start with a low plate voltage and increase that step by step, but don't run them without plate voltage.

Best regards

Thomas
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Old 28th August 2012, 01:29 PM   #5
Doz is offline Doz  United Kingdom
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I burn in EF86's. Half heater volts for a day ... apparently the noise floor drops. Damned if my tin ears can hear it though !
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Old 28th August 2012, 01:30 PM   #6
TheGimp is online now TheGimp  United States
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For noval tubes, I bake them in an oven at 350F for four hours, and allow to cool before using.

Prior to this I just plugged them in and ran them. I experienced several failures (6F4P specifically). Since baking them I have experienced no failures.

The theory behind this procedure is that heating them helps to activate the getter to remove trace gasses.

ymmv.
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Old 28th August 2012, 01:32 PM   #7
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Morgan Jones suggests an oven bake and has some data to back that up. I run the heaters for an hour or so, then apply plate voltage. That's not long enough to poison the cathode (a real issue) but long enough to get everything nice and warm and encourage outgassing and gettering.

Nothing wrong at all with what Thomas suggests, and it may even be theoretically better, it's just a bit of a PITA.
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Old 28th August 2012, 03:00 PM   #8
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Try running them whit some alummina foil over them. to make sure the getter spot gets Hot


A lot of tubes are just burned in at the factory whit AC on the tube and a lightbulb to limit the current. Works fine and keeps the equipement used simple.


cathode activity on poor tubes can be brought back to usable if you run the heaters Hot (not only for thorium coated tubes)

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Old 28th August 2012, 04:20 PM   #9
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I haven't found it necessary at all with small signal tubes, but have found it necessary with 6C33 for best reliability, and for some large DHTs as well.
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Old 29th August 2012, 12:18 PM   #10
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Hi all,

Thank you for your comments and knowledge.
For my little understanding of physics and chemical reactions the getter should do all things well. After manufactoring the getter absorbes any gas influence of the vacuum. This can only be some rest of gas inside the tube, gas particles from internal structure ( desoprtion ) or very small ( a few molecules ) from outside of the tube ( permeation ). So far I understand all relevant gas parts of internal material is set free by heating the tube extremly while evacuate ( create vacuum ) on manufacturing. Fireing the getter later will bind the rest of gas. All tubes, especial the military ones, are burned in to verify thier parameters.
For that I see no really physical reason why a NOS tube should burned in. Nevertheless I will run the tubes in circuit for 24h to reach the operating temeratur of all components and measure if I inside the given parameters.

Thanks a lot for this enlighting discussion.

Karsten
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