It's 6.3 volts * SQRT(2) less two diode losses. If one uses a SCHOTTKY bridge with a really low forward voltage, and uses the low-dropout regulators (LM330T) in place of the LM309's or LM340T-5's, one can use a heater transformer just fine. The empty slots won't need much power and, unless you use 16 of the old 4K SRAM boards, your power requirement will fall within what that 12Amp model can do. One shouldn't try to save on the filter cap's though, and, BTW, and should put a very low value (~0.25-ohm) resistor between the bridge and the filter caps to protect the diodes at turn-on. If there's a real need for lots of power, one can parallel two of these heaters provided the phase is correct. I've got one transformer downstairs that is about he size of half a watermelon, weighs on the order of 35#, and has all the requisite voltages plus a few others I decided I didn't need. I also don't look forward to lifting it. Dick ----- Original Message ----- From: "Don Maslin" <donm(a)cts.com> To: <classiccmp(a)classiccmp.org> Sent: Wednesday, August 29, 2001 1:02 PM Subject: Re: S-100 Power Supplies: thanks!

That's a reasonable alternative, but provides less power, since it only rectifies half the available cycles, so q/t is lower, though not halved. Ripple is likely to increase, though. In any case, it's as I often say, "Where there's a will, there's mourners..." If he really wants to do this, a little calculation will tell him how much power he needs, a little more calculation will tell him which of the methods I previously mentioned will be needed in order to reach his goal, and a meter on the transformer when it's loaded with an appropriate load resistor, will tell him what the AC voltage he has to work with under full load is. Different manufacturers interpret that differently, though I suspect that valve heaters are pretty similar. If he has a 6.3 volt output at full load, he'll certainly be able to do the job with a schottky bridge and a series resistor, and may not even have to replace the classic regulators with a low-dropout replacement. Moreover, since it's unlikely he'll be operating at the full load current, or anywhere near it, he'll probably have on the order of 5-10% headroom without objectionable ripple if his filters are large enough. I've got one system with 800K microfarads at 10 working volts as its filter, with just such a low-voltage transformer. The low voltage is high enough to feed the regulators, yet low enough that heat isn't a problem. Dick ----- Original Message ----- From: "Tony Duell" <ard(a)p850ug1.demon.co.uk> To: <classiccmp(a)classiccmp.org> Sent: Wednesday, August 29, 2001 4:56 PM Subject: Re: S-100 Power Supplies: thanks! bridge a resonable alternative, though that wasn't on his list.