Thanks ! Its built for fun really, and to power radio gear, typically all of it. Yet its the amplifier that draws all the power at 100 watts. For future proof and the option to use 250 watts, I don't actually get the RF output rated by the manufacturer, so the 100 watt unit gives me around 80 watts or there abouts. I might never use 250 watt amplifier, but the power would be there if I wanted it. In years gone by I've used 400 watts and purchased a huge smps psu especially to power it. But ive been converting a few ATX units, and old server psu's with mixed results, the power is always good from these. But as its for RF use the noise can become a problem at high currents, the ripple noise.
So having built a couple of low current linear power supply's, nothing exceeding 5 Amps, I thought its about time to build a high current unit. And searches lead me to the voltage regulator emitter follower circuit, its parts count and simplicity looked interesting for what it was. Then my question was.. Does it work ? After building two versions, a single and double transistor version, I discovered it works quit well (the double transistor version in use 24/7) This is still fine 1 month in now.
So its time for the six transistors version now. My searches lead me to many circuits, some using dedicated IC's that look very interesting, and having looked inside retail linear supply's over the years I recognised the circuit in these units.
Yet I was taken with simplicity, parts count, and cost. After trying the two transistor build, and its performance over all, I think it could do the job. After measuring voltage, current, and heat, it voltage drop under load improved with the addition of the second transistor, by a good margin. So looking at this so far, and having tried it, I'm confident its worth a try to build a six transistor version.
From the original TIP2955 transistors, I started looking at more powerful alternatives, that lead me to the MJ11015 and the MJ11033 transistors. I've ordered 6 x MJ11015 transistors now, the MJ11033 transistors where a bit to expensive for additional power I would never use. So back to this thread, that's what lead me to the protection circuit, the mains input poses no real problems, but over voltage on the secondary final output would equal an expensive fault in an over voltage situation. I once had a retail linear go high voltage, instead of 13.80 Volts on its rated output, it developed a fault and put 23.00 Volts into my radio gear destroying it.
After a good look a figured a potentiometer wiper lost contact withcits track, this sent the voltage high, I've since learned if the designer had tied the other leg of the potentiometer to ground it might not have destroyed my radio gear. So that's it really, I got into doing different things with modifying reclaimed smps units and building simple linear psu units.
That's a big transformer and bridge rectifier you have there ! So now a bit more research on the crow bar circuit, and sourcing a decent enclosure. I am a bit of a perfectionist and can't stand ruff and ready final results, its got to be as good as I can build it inside and out. Thanks again for the help.