I've tested the filament on the 3cpx5000a7 without air flow but with
filament running less than 15 seconds. I personally would not fret over
hooking the 8877 filament up without air flow for a very short time, say 10
second, maybe a little longer. Jim has pretty much proven that it will not
damage the tube. I would allow for a substantial cool down period before
doing it again.
Larry N5BIP
Jim Wrote:
I just checked fil voltage on my 8877 here (No blower ) watched it ramp-up
to 4.9vac in less than 10 secs and then pulled switch...No heat felt on tube
base in this short time interval...What`s the big deal unless you want to
test with rf conduction?(I do that too but with blower running&safe
connections) Jim K7RDX..
> Rick Stealey wrote:
> >I will soom be ready to apply power for the first time to a homebrew 8877
> >amp. I need to make adjustments under the chassis with the tube filament
> >lit and was wondering how long I can run the 8877 with just filament
voltage
> >applied and no air flow? I don't see the subject addressed in the Eimac
> >spec sheet.
> >
> I can't answer that question directly, but how about stretching clear
> Saran wrap over the base of the chassis?
>
> It balloons up alarmingly, but it keeps the air in, lets you see what
> you're doing, and it's no problem to poke screwdrivers and trimming
> tools through it (the small holes they make don't affect the cooling).
>
>
> --
> 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.co.uk/g3sek
>
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