[Amps] Burn in Question - 811A tubes

[pegasus at mho.net]

Hi Dan...
    I have a "sense" of what is common practice among seasoned hams who
have learned through experience on such matters.
  Generally with new tubes you don't have to do a "burn in".  They are run
at the factory before release.  Eimac runs the filaments extra hot at
the factory  for some time before releasing them.  I'm sure 811s go
through a similar process.  The only time where a burn in seems to be
useful is when powering up a tube which has not seen service for a long
time.  If some gas has leaked
 around the seals from years of sitting unused and high voltage is
applied, they could arc internally and destroy themselves.  The solution
(if the gas isn't excessive) is to run the heaters (without HV applied!)
for some 20-30 hours.  This "getters" the gas and restores a more perfect
vacuum.  I would also do this run-in on a "new in box" tube that is more
than a year or two since manufacture.
   Another cautionary note applies to used tubes.  New tubes can usually
withstand the rigors of shipping.  But after considerable time on the
tube the filaments become thinner and somewhat brittle thereby more
suseptible to damage from rough handling.  I've shipped a perfectly
good 4-400 in a well packed cushioned container only to have the
filament in pieces at destination.  So it's wise to handle used tubes
even more carefully.
  These are opinions based on discussions with Eimac personnel and
hams/engineers with far more experience than myself.  But we're always
ready to hear more.
Good luck and let us know how the 811s work.
Dennis


> I am installing a new set of 811a tubes into my Ameritron 811H (4 tubes).
> When I did years back I did do a tube burn in. Does the group still feel
> that is good practice? If so I can not remember how long I let them just
> sit seemed like 8 to 10 hours. Does that sound right or where can I look
> for the proper length of time to burn the new tube in on the amp?
>
> Thanks
>
> Dan