Author Topic: New Power Tube help.. Preconditioning??  (Read 7678 times)

Offline sleepyguy24

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New Power Tube help.. Preconditioning??
« on: November 01, 2013, 08:05:06 AM »
Hi everyone.

I saw this in the Audiogon forum and I think is pretty interesting regarding new power tubes. I think it is from the head guy from Atma-Sphere.

Quote
One way to reduce arcing on otherwise new tubes is to light up the filaments of the tube without applying B+ to it. Leave it in this state for at least 4 days and nights.

This process is called preconditioning and should be done with any new power tube that has not been used before (if it has been used, preconditioning will not do any good).

**Preconditioning will double the life of any power tube.**

It will also substantially reduce arcing failure that otherwise occurs shortly after installation, due to the tube being unhappy about being shipped. You can see that this is a big deal. I may be giving away a little secret here; this may be why the more expensive tubes seem to hold up better. (It appears that the process of preconditioning uses the filament heat to cure the cathode coating, which otherwise can flake off the cathode fairly easily which is the cause of arcing failure.)

If your amplifier does not have a Standby function (Standby on most tube amps is where the filaments are lit up but the B+ power supply is not running), this might be difficult to pull off. But setting up almost any power amplifier with a Standby switch is a fairly simple matter, although one that should only be done by a qualified technician.

Have any of you tried preconditioning your new power tubes? Have you noticed an improvement in power tube life? I'm still stumped as to how pre-conditioning can be done.


Offline Triode Pete

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Re: New Power Tube help.. Preconditioning??
« Reply #1 on: November 01, 2013, 07:25:54 PM »
The good tube companies, especially the now-defunct ones, always burned-in & tested their tubes for quality. Western Electric, Sylvania, RCA, Ken-Rad, Tung Sol, etc. had extensive testing & burn-in rigs. If one failed, they would destroy the entire lot... That's Quality Control!

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mgalusha

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Re: New Power Tube help.. Preconditioning??
« Reply #2 on: November 07, 2013, 12:28:23 PM »
For low mu power tubes like the 6AS7 used in the Atma-Sphere amps it does seem to help them live longer and be more stable. One time I matched a batch of 100 of these, I cooked them in sets of 20 for about 5 days per set, took a month just to prep get them ready for testing.

I did try testing a few that were not conditioned, they seemed more variable than the ones that had been run with no plate voltage for a while. My shop stayed very warm for that month or so. :)

Russian_Glass

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Re: New Power Tube help.. Preconditioning??
« Reply #3 on: August 04, 2014, 07:15:59 AM »
With new-production tubes, it should not be necessary.
With NOS (New Old Stock) tubes that have sat on a shelf a number of years, "re-gettering" these is not a bad idea.  It doesn't take days though.  Usually a matter of hours will re-absorb any air that has leaked in.
I quote Econco (rebuilder of high power transmitting tubes) here:
"Tubes that may have gassed up can be partially
degassed by putting them in the equipment and running them for several hours with filament voltage only applied.
After the initial filament-only degassing, operation for an hour or so at reduced
plate and screen voltages is desirable. This allows the getter to soak up and hold
any residual gasses. In directly-heated filament tubes, the getters are
generally zirconium-bearing materials, which depend on heat to activate the
gettering action."

As it's not always possible to do this in situ, I recommend making a "jig" of a spare socket (for any tube replaced regularly) and a 6V (or 12V depending on filament voltage) laptop power supply - (these typically supply 3-6 amps, enough for even a 6C33C).

If this is still impractical, you can look up the tube's operating temperature on its data sheet - (this can be anywhere from 200°F to 500°F) - and bake it (in an oven) at that temperature for 4-5 hours. (If the tube has a bakelite base, zip-tie a strip of potholder around the base to keep it from cracking).  When finished, shut off the oven and let the tube(s) cool gradually inside the oven.