Hi David,
Been there, done that.
http://qsl.net/wc6w/wc6wamps/index.html?fr63.html
Though the amp didn't end up small nor lite!
http://web.archive.org/web/20010825210138/http://www.angenent.org/W7IUV/wc6w/wc6w_1.htm
The switcher may be just be glimpsed under the Pi coil in the photo on the
left side at the bottom of the page.
What about an SPS for the plate supply? Far greater potential/size weight
savings there!
73 & Good morning,
Marv WC6W
http://qsl.net/wc6w/
--- On Tue, 6/28/11, Dr. David Kirkby <david.kirkby@onetel.net> wrote:
> From: Dr. David Kirkby <david.kirkby@onetel.net>
> Subject: [Amps] Using switch mode power supply for heater power
> To: "'AMPS'" <amps@contesting.com>
> Date: Tuesday, June 28, 2011, 5:57 AM
> I'm looking at building a 4CX1000A
> amp, which I want to make as small/light as
> practical. Using an SMPS for the heater would go some way
> to this, whilst
> offering regulation, since my own supply varies by more
> than +/-5% and a
> generator would vary even more.
>
> The 4CX1000A needs 6.0 V at 9 A, but of course when cold it
> will be a very low
> resistance. I thought of using a 7.5 V 13.5 A switch-mode
> supply, with a 0.17
> Ohm series resistor to drop 1.5 V. But I'm concerned the
> heater will never get
> hot, as the cold resistance of the tube will draw too much
> current, causing the
> SMPS to shut down.
>
> If I bought one rated 12 V at 18 A or more, then dropping 6
> V across a 0.67 Ohm
> series resistor would mean the current would never exceed
> 18 A, even if the
> heater is a dead short when cold. But that's a lot of
> wasted power, and an
> over-specified (i.e. expensive, heavy) power supply.
>
> Another option might be a NTC inrush current limiter. I've
> not looked at what's
> available, but I do know device exist for this sort of
> task.
>
> Does anyone have any ideas on the best way to use an SMPS
> for a heater supply?
> --
> A: Because it messes up the order in which people normally
> read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
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