Getting old transmitting tubes ready for service

[w1vtp]

Well, as construction of my new shop comes closer, I'm thinking of my collection of 813s and how to safely get them ready for service.

This guy has an interesting technique

http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm

So, the way I read this, I should set up a test set where I can apply each of my 813s such that they can be "cooked" using relatively low plate voltage (maybe variaced down) and some positive control grid bias.  Then proceed to cook each tube.  First part of the process would be to let the filaments run at voltage -- say 24 hours -- then slowly bring up the plate voltage until the tube is run as some % of full dissipation.  Metering the control, screen grids and plate current would be mandatory, I would think.

Thoughts?

Al

[WD8BIL]

Bob W2SM has been doing this for years.

[AB2EZ]

Al

Assuming the tube has not developed a leak in its vacuum... the objective is to reabsorb molecules of gas that have been released, during long term storage, by the materials that comprise the tube.

In high power tubes (like an 813) the "getter" that absorbs/reabsorbs these molecules is the plate... when it is at a high temperature.

So, if the tube is usable... after a long period of storage ... you want to get the plate to close to nominal operating temperature by applying a moderate amount of plate voltage (maybe half the rated voltage); and adjusting the DC grid voltage to cause a moderate amount of DC plate current to flow (to get the plate to glow dull red).

Depending upon the tube... there is a probability that the plate will be able to reabsorb the accumulated free molecules inside of the tube; and therefore become usable. For some tubes, like 3-500Zs, the probability is (unfortunately) no that high. If the plate doesn't reabsorb the molecules of various gases that have been released during storage... then the tube will arc over when you try to use it at full plate voltage, with rf applied to the grid.

Stu

[W1RKW]

So what Stu stated but instead just put the 813's into service and beat the pants off them for a period into a dummy load.  That's what I did but it didn't seem to make much difference in the end. They all seemed equal in output and stability.

I have many 813s for my rig that I collected  prior to putting the rig on the air. When I was having problems during construction, I swapped out a bunch of the tubes thinking they were the issue but found none of them made any difference which turned out to be some other problem with my construction.

Naturally, you'll want to screen them for shorts outside of the rig so you don't blow up a transformer or something but if the rig construction is sound, put them into service and run them.