[AMRadio] 813 question

[W5OMR/Geoff]

Jim Wilhite wrote:

> Don't know about the Russian tubes, but tubes shipped from Eimac had 
> an instruction insert that said to burn in the tubes before applying 
> power.
>
> Since there is no such thing as a perfect vacuum a small amount of gas 
> is left in a tube.  That is the purpose of the getter, to absorb those 
> gasses. If I were installing a very old tube, say a 304 TL or 250TH or 
> high power tube in a circuit, I would burn it in for at least an 
> hour.  As I recall the instructions for the 4-X series of tubes called 
> for about 30 minutes. 


One of the 'ebay special' 250TH's I got, claimed to be NIB... after 
30mins with the filaments on it, I hit the grid drive on the tube, and 
it turned blue inside, like an 866.

If that's the case, in the larger tubes, I'm think there needs to be 
-more- time for 'burn-in'.  30 mins didn't get it, for me.


Then again, the base wasn't loose, either, after 30 years of sitting 
around...

--
73 = Best Regards,
-Geoff/W5OMR