Quote:
Originally Posted by dslknight
Could you recommend any references for a beginner so that something like this could be made later on down the road? I'm willing to do anything short of obtaining an electrical engineering degree to learn.
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This
PDF from Hammond outlines much about figuring capacity and approximate outcome of various bridge and transformer combinations. Very useful, though it does not cover losses to specific tubes.
The other tool that is valuable is as motherone pointed out- Duncan's PSU Designer II. It covers both SS and VT rectifiers in various configurations, though there are no models for a hybrid bridge. I got my model as close as possible using a SS bridge model, figuring in V losses to a 12X4 rectifier. Then I built it on a slab of plywood...
...and measured the actual results, making a slight adjustment to the dropper resistor to tweak the loaded output reading. It was pretty close though.
I have no specific qualifications regarding EE myself, I am just an avid hobbyist, who also learns from his mistakes.
If you understand the data in the Hammond PDF, and understand Ohm's Law, then you can cobble something like this together. I did spend a few weeks worth of spare time swapping parts in and out of the simulator, comparing ripple, rise time, loaded and unloaded output, etc. It's not infallible by any means, but it is an excellent tool to aid in visualizing 'what if...'. Way faster than breadboarding, but as you can see, it is not a replacement for it. It is a great preliminary supplement to it.
So while I can highly recommend a tool like PSUDII, I do not think it should be used in place of physical testing. Even programs like SPICE sometimes offer results a bit different than actual solder and wire will show, coupled with components and conditions being somewhat inconsistent. It's always good to break out the parts and build it, without worrying about casework at first. It goes a LOT faster when you remove that factor, and the results are tangible. Just be careful (obviously) when working with either tubes or mains power, as you can be dead in a heartbeat if your hands wander. It's safe enough if you treat exposed circuitry with the respect it deserves.
I've done this already, but I have to credit Lloyd Peppard for his help as well. I was up front in asking his assistance, and outlining my plans. I even bought a kit from him without the chassis, which he was happy to do. I have to support him, too. He couldn't be a nicer guy. He, as well as Pete Millett, and Andrea Ciuffoli have all developed projects utilizing a hybrid VT/SS bridge rectifier, and all seem to enjoy the result. In fact, the original Mapletree Ear amp had a hybrid tube rectifier setup, as you will see the fourth tube. A lot of folks assume that it was the extra tube for a preamp output, since the hybrid setup is not available anymore. I went ahead and configured the added choke and cap filter on my own, using PSUDII to see what it looks like.
Motherone: Thanks a bunch... I am really happy with it. I was quite reluctant to do this, for fear of ending up with an amp that did not sound as good as the original, which I liked very much. The initial project was mainly to accomodate a switched input, and a nicer chassis. Then it expanded to include room for a better attenuator in the future. And what the hell, I had room for a better PSU, so why not try to do that, too.
