Simple circuit, say 9V AC to a regulated 6.3 V at at least 2 amps?

[Chris Wilson]

richard.cs: I have a small 1 uF 50V electrolytic on the output side. As per a spec sheet I was working off. Should I go bigger?

Great info, you have all been very helpful and patient! Next I need 12.6V at at least 7 Amps, the amp guru who specilises in this Russian beast uses Chinese switch mode supplies for this. As richard.cs mentions, I am in the realm where a switcher should be the way to go there.

I am also playing with a 50 volt SS linear, and have bought an HP rack server 50 volts at 50 or 60 amp switch mode supply off Ebay, dirt cheap. Beautifully made, they probably cost a lot of dosh new! There's a small preset pot inside to trim the voltage. I have found someone who has added some RF caps to stop RF getting in, and changed the preset to give a bit more voltage adjustment range. I am wondering if the big 1300 Watt rack server 12 volt power supplies can similarly be trimmed. There can't be a cheaper way of getting a genuine 100 Amp 12 volt supply!  Anyone been inside one? I assume they all must have some sort of regulator device, which can be trimmed with either a preset or a resistor change to a preset? When I look at my Farnell 60 volt, 50 Amp supply, that I can only JUST lift, but not get on the bench on my own, and the HP one that's very compact and light, I can see switch mode is the way to go. The 50 volt HP one I have emits no detectable RF noise, either, certainly on the HF bands.

[richard.cs]

richard.cs: I have a small 1 uF 50V electrolytic on the output side. As per a spec sheet I was working off. Should I go bigger?

These are generally minimum values for which the regulator is stable. There's no harm in going larger. It usually has a fairly small effect on output ripple (but still some effect) and a larger effect on transient response (which isn't really relevent to you with your fixed load).

Many of the fixed 12V power supplies can be trimmed easily within a small range but have overvoltage protection that needs to be disabled before you can go very far. For 12.6V you'll almost certainly be fine but anyone wanting to go to lead-acid charging voltages (13.6V to 14.4V) usually has to disable or modify the overvoltage shutdown. This is common with PC power supplies and I imagine server ones would have similar protection circuitry. With all the tweaks done the 12V ones can usually cover about 8-16V output but possibly not over their full input voltage range.

For a cheap 12V 7A switching supply I would be inclined to go for a small modern PC PSU, the older ones were only a couple of amps on 12V with all the power on 5V and 3.3, the newer ones deliever a lot more at 12V straight into switchers on the motherboard. There are also auxilliary ones availiable meant for graphics cards that are 12V at 10-20A without the other outputs.

[dr_p]

The valve data sheet says 0.55 Amps each filament, so I am playing a bit safe on speccing 2 Amps. Cheers!

LM317 can supply 1.5A (min) to 2.2A(typ) if you have a low input-output differential, so that's a choice as well.