> From: "Ian White, G3SEK" <G3SEK@ifwtech.demon.co.uk>
> Subject: Re: [AMPS] two questions
To: <amps@contesting.com>
> Date: Sat, 6 Sep 97 07:43:25 +0000
> A number of VHF mountain-toppers are using modified computer switch-mode
> supplies for 6V heaters, to avoid problems with generator sags and
> surges. Apparently the fully-enclosed and filtered units work well, but
> I'm sure an open-frame or unfiltered switcher would be a disaster on
> receive. Also, this is information relates to VHF - suppression of
> switching transients may not be so good at HF.
>
> Bottom line: it's worth a try.
But be careful!
The LAST thing you want at turn on is a stiff voltage regulated
supply! It would be inrush city for the filament.
Also, many supplies have fold-back current limiting. Those supplies
will often NEVER come out of limiting and run a filament!
Finally, if the supply does come out of limiting slowly, the filament
warm up time is increased. If you use a MOX cathode tube you could
strip the cathode from insufficient warm up time with a fold
back current limited supply, IF it ever comes up at all.
By the way, the largest failures in amateur PA tubes are NOT related
to excessive filament voltage . The most common
non-tube-manufacturing related defects are gas or dissipation
related damage, not low emission or open filaments.
73, Tom W8JI
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|