> Dont know who manufactures these beasts but RFparts sell them....
> I used two as filament inrush limiters in a single 3-500zg 50 mhz amp ....
> One point to consider in using them is that if the supply is switched off
> and them back on before they go cold they no longer limit the current!!!!
>
> 73
> Stephen G7EUW
Unless you use a greatly oversized transformer and oversized
leads and chokes, most inrush worries are a waste of time.
Inrush was a craze in the 70's, like parasitics are today. All the
problems you see mentioned today with tubes and attributed to
"parasitics" were attributed to inrush years ago, when that was the
popular hysteria.
Inrush is more of a problem with large MOX cathode indirectly
heated tubes, like the 3CPX5000. That tube can draw excessive
current for many many seconds at turn on. Inrush is also more of a
problem with series filaments.
The best thing to do is measure the inrush. In most cases you'll
find you are worrying about nothing. The exceptions are generally
when the filament winding is on the plate transformer, or you have
unwisely oversized the filament transformer and filament wiring and
wire sizes in the filament choke.
NEVER use a globar unless you have a way of monitoring the
filament voltage , and if you slow-start a MOX cathode tube be sure
you extend the warm-up time enough to makeup for the delay in
heat at the beginning.
73, Tom W8JI
w8ji@contesting.com
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|