using old tubes first time

[Turbon]

I saw in some videos that getter is activated by means of a strong RF filed, as the support is a shorted turn, it becomes very hot when a RF field is near it, as a shorted turn transformer. And it becomes very red, far from 80°C.

So should we bake them in the microwave oven? .

Probably NOT

Regards

 

[DF96]

I believe that in the factory, the heater at higher than normal voltage is used to activate the getter, this process is (was) called flashing.

You are confusing cathode activation (very hot heater) with getter activation (usually via RF induction heating).

My understanding is that getters work better when hot, so a valve which has been unused for many years may need a while to soak up any gas. However, in most cases this happens safely during normal operation in a well-designed circuit; all you get is a bit more grid current for the first few hours. A circuit which has too high values for grid leak resistors may cause trouble during this period, so if worried check the circuit against the valve datasheet.

 

[Turbon]

You are confusing cathode activation (very hot heater) with getter activation (usually via RF induction heating).

My understanding is that getters work better when hot, so a valve which has been unused for many years may need a while to soak up any gas. However, in most cases this happens safely during normal operation in a well-designed circuit; all you get is a bit more grid current for the first few hours. A circuit which has too high values for grid leak resistors may cause trouble during this period, so if worried check the circuit against the valve datasheet.

So, 80C in an oven for a few hours if we do not have an RF heater... What other options do we have?

Regards

 

[rsheptak]

Getters are Barium, right? Barium continues to react with gasses in the tube even after flashing. On heating, some of the metal components of the tube offgas for a while after manufacture, and the barium takes care of that. If the barium flash starts to look thin, traslucent along the edges, or redish brown that indicates the tube has a leak, though has not failed. Heating the tube up to 80 degrees C. only marginally increases the speed of the barium reaction.

 

[JPeitzman]

Tubes use in OTL amp are well known for arching...?

I know somewhere between very little and nothing about OTL amps, but I'll take a stab in the hopes that I can be educated. Is this arcing due to a plate to cathode short from the tubes, already being run near their limits, being over driven? Wasn't this a somewhat common failure mode with 6AS7's? I didn't think that sort of arcing had to do with a gassy tube. If the tube is in the circuit and running, then arc, it should already be hot enough to do the same job as the oven so gas shouldn't be the cause.

As for the drop in transconductance, could this be caused by a small separation of the cathode coating and the physical cathode due to the arcing? This was something (I thought) could happen with tubes used in computers and other pulse applications. I could be completely wrong though, that's the fun of learning

So, 80C in an oven for a few hours if we do not have an RF heater... What other options do we have?

...in most cases this happens safely during normal operation in a well-designed circuit...

I mean, I'm in no way trying to say don't heat your tubes in an oven. Theoretically, if you are trying to speed up the reaction rates of the gases within the tube with the getter flash material I get it. I'm trying to learn and understand if it is necessary when applying power to the filament in a controlled manner seems to me to accomplish the same goal.

 

[Koonw]

If the there is some residual gas (include some inert gases) , arcing is worsen by certain factor. If 6SA7 arcs over at 150V with gas residual, and if the gas has been cleared, it would not happen or reduced to very low probability. Once it arcs, it will not happen again, so the gas must have been consumed somehow, so no or low gas no arcing, more gas more arcing..

The heat alone from heated filament is not sufficient as they said, that is why in the oven, or any external heat source. In other cases arcing damaged the grids, so that turns the tube into a different one, so if not then would be plate and cathode, with damage to cathode coating which lower the current capacity.

 

[petertub]

So, all that is happening is that by placing the tube in an oven at 100C, or there about, you are increasing the rate of reaction of potential gases within the tube with the getter flash material. That is sound, but why would a controlled warming of the filaments not accomplish the same thing?

If a tube is arcing due to gas you likely have a pretty gassy tube, I'd say that tube is done. I would be skeptical that an arcing tube, due to gas intrusion, could be saved by a couple hours in an oven. We are talking real catastrophic arcing here, not ionization.

Heating with only filament will not heat the tube top where the getter is located.
Yes, the tube might have some gas after long storage. Thats why one should
give the getter a chance to suck up that gas before applying B+, sucking up
gas remnains is what the getter is made to do.

 

[grimberg]

A few view points that I have never heard before. Unless a tube is actively leaky, I would think that the vacuum would remain the same. I have never heard of baking the tubes in an oven to reactivate the getter or that the getter "goes to sleep".
Can you expand on this and possibly point out some references for this?
Thank you

BillWojo

In my view you are correct. However, pay attention to these words: "Most or all audiophiles...". That puts what follows it outside the realm of reality. It is a trip to fantasy land, where cables conduct better in one direction than another and electrons are modified by the conductor they have just crossed.

 

[JMFahey]

Baking a tube in an oven is *NONSENSE* .

Neither 80C or 200C or any temperature achievable in a home oven will do NOTHING.

Besides, NOT EVEN THE TUBE FACTORY DOES THAT, for the very good reason that not only will it destroy the tube (making the bulk or all of it reach metal evapporating temperatures) but also needs a *cold spot* so such metal can condense.

Not possible if all of the tube,specially the glass,is at a high temperature.

Flashed getter –
The getter material is held inactive in a reservoir during assembly, then heated and evaporated after initial evacuation, usually by induction heating. The vaporized getter, usually a volatile metal, instantly reacts with any residual gas, then condenses on the cool walls of the tube in a thin coating, the getter spot or getter mirror, which continues to absorb gas. This is the most common type, used in low power vacuum tubes.

Activation

The typical flashed getter used in small vacuum tubes (seen in 12AX7 tube, top) consists of a ring shaped structure made from a long strip of nickel, bent up into a long, narrow trough and then folded into the ring shape ...... an R.F. induction heating coil connected to a powerful R.F. oscillator operating in the 27 MHz or 40.68 MHz ISM band is positioned around the bulb in the plane of the ring. The coil acts as the primary of a transformer and the ring as a single shorted turn. Large R. F. currents flow in the ring, heating it.

“Flash getters are outgassed at temperatures between 600 and 700 C, usually by r-f heating from the outside of the tube, and flashed at temperatures between 900 and 1,300 C.

Try THAT in a kitchen oven