The AM Forum

I read on aVT-4-C GE tech sheet about running a filament without any plate voltage applied is good for overdriven tubes. Is this a requirement for tubes that have been sitting for years also?

I would think that this would be a consideration if I want to further test these.... outside of an ohmmeter test of a filament?

Thanks,
Bob

http://www.tubecollectors.org/archives/vt4c.pdf

Page 3 of 4 specifies this procedure for this specific tube for a specific situation.

Many later tubes used a zirconium coating or a zirconium plate alloy for gettering, so I wouldn't think this procedure applies to all tubes.



Phil

Thanks Phil, I had been looking at that sheet.

I've Google'd and found someone calling for 24 to 48 hours of burn in time of the filament to remove gas from old tubes before testing of the tube.
So could the tube be damaged ( filament ) if this isn't done?

Running the filament in a graphite-anode tube won't do much in terms of gas.

If the getter flash is shiny silver with no rainbow, it is 99% good.

I have successfully de-gassed many vintage transmitter tubes via an ion-pumping scheme worked up in the 50's by the engineers at WOR-AM.

It involves high voltage AC and NO filament lighting.

73DG

Is there any chance that would work for an Eimac 250TH that glows like a VR tube with 150 volts DC on the plate?  I would like to hear more about the procedure.  Or should I just move on to more scroteful external anode Eimac triodes and tetrodes?

I'm trying to determine if a vendor with an Amplitrex tester had done something wrong or if the filament exploded in transit. I packed six of these and shipped to the guy. Got a compliment from him for the packing and then came back in the same box. Two out of the six sustained filament damage.
The report recorded a heater run time of 13 minutes. 500 volts on the plate.
So that is why I was inquiring about a proper burn in time for a tube that hasn't been lit for at least a decade.

I had a vision of a heated tube being pulled from the socket and laid flat possible causing stress of the filament.

He also doubled the testing price after he did mine, and wrote to me that "they take way too long to test" which also made me wonder if he was forced to rush thru the testing because of profit considerations.

Probably more like shipping damage and a tough lesson learned, and I'll never prove that he may have done something wrong!

Bob

It is amazing that those bottles were once thrown away or sold for less than 75 cents each...
They are listed on this TAB tube sheet from 1957. Tab never advertised them after 1960! They were not worth shipping!

They are listed here can you find them and the price?

VT-4-C  = 211

If the 2LL on the sheet was a misprint and should have been the 211 then it was listed for $0.45

I'll take 1000

Beautiful.