[Amps] 3-500 burn in

[Rob Atkinson]

Not sure if this applies to your tubes but I think RF Parts recommends
a few hours of time with the amp on standby with the filaments lit if
they are thoriated tungsten.  I usually let my amp sit with the
filaments lit for 3 to 5 hours (I just turn it on and go about my
business for a morning) if I have recently purchased tubes in it and
I'm firing them up for the first time, or tubes that have been sitting
for a few years and I have just swapped them in.  You don't know how
long your new tubes have been boxed on a shelf somewhere do you?
Anyway, go to the link below and read the part about Tube Burn-In.


http://www.rfparts.com/tubeapp.htm

Here's the pertinent part for hams:

It is well advised to allow tubes to operate in standby mode
(filaments on, no transmit) for 2-3 hours before tune-up.  The 811A,
572B, 3-500Z, 4-400, etc. utilize a thoriated tungsten filament, which
is highly dependent upon sufficient filament temperature to provide
adequate electron emission for normal operation. Emission increases as
the thorium migrates towards the surface of the filament wire. This is
why it is recommended to "burn in" these tubes before operation.

73,

rob / k5uj