[Amps] Switching PS for filaments?

[Ian White GM3SEK]

Peter Chadwick wrote:
>One problem that can arise is if the psu doesn't like providing the 
>excess amps when you first switch because the filament is cold. I got a 
>5v 15A one for my 4CX1000 (yet to be built) amp: it won't start with a 
>cold filament. It's possible some constructive step start or voltage 
>ramping is needed.

Voltage ramping can sometimes be as simple as "slugging" one side of the 
master potential divider with a large electrolytic, but it still doesn't 
guarantee that the switcher will allow itself to start at near-zero 
voltage output. Some will, some won't.

The add-on circuit posted by WC6W yesterday looks like a good solution, 
because it allows the switcher to start up as normal, and then gives a 
gentle ramp of current into the tube.

Nice one, Marv:
http://wc6w.50webs.com/wc6wamps/index.html?fr64.html


-- 

73 from Ian GM3SEK