3-500 filiments

[James Hill]

I can not recall what the problem was with leaving the filiments on without high voltage.  I first heard of this many years ago when I was working for a television station.  We wanted to use our old transmitter as a hot standby but the tube manufacturer recommended against leaving the filiments of the power tubes on without high voltage.  We had to rig up a dummy load for the IPA with a Dow Key relay to switch between the dummy and the PA.   Unfortuently the fellows I worked with have all since passed away and I just don't recall much other than some of the power tubes in the transmitter could not have filiment voltage only, per the manufacturer's warnings, for extended periods of time.  I am sorry my memory is so bad as to the reason. 
I doubt that the little 3-500 would have the same issues, but I don't know.  However the manufactures spec sheet would tell us.   Jim

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