One problem in designing such a power supply is the short-circuit current-limiting aspect of the design. BJT's have a horrible 2nd- breakdown effect that will greatly exacerbate your design problems. To get an idea of the problem, study the BU508's SOA curves. Ouch! For example, at 40 volts, you're allowed 120 watts of dissipation, but at 400V you're allowed only a wimpy 36 watts!!! These are 25C values, which have to be derated as the transistor's case heats up. I recommend that you use high-voltage MOSFETs as pass elements, and avoid the issue.
The Heathkit supply is nowhere near the quality of the Lambda and Kepco supplies that are available just as cheaply. However, with refurbishment, the Heathkit will do okay.
Glass Audio ran an article by Bruce Rozenblit on a very nice bench supply you can build some time ago.
I prefer using a homebuilt HT supply which consists simply of a off the shelf power transformer-mine is that of a Fisher receiver whose OPTs went into Fender guitar amps-with diodes and caps I can just plug into a Variac or into the wall for rated voltage, with nice recessed test ports. I have a (shortable)light bulb socket in series with the primary. I only use the HT winding, I use, and you should own, a variable DC low voltage supply. Mine is a commercial Asian made one, but older HP, Sorenson, Behlman Invar, Tek, or Lambda ones are hamfest constants, or you can build one. Joe Carr has a good book with nice plans. A Schauer or Schumacher garage sale battery charger can be salvaged for a power xfmr and case.People throw them out all the time when the leads are bad.
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I would very much like to have some ideas, schematics, tips on how to design a lab power supply for experimenting with tube designs. The specifications could be like 0-500V 0-100mA... (+/-?)
I would like to build a good regulated power supply. Could i just design it like a normal low voltage PSU? like a opamp, voltagedivider, a BU508 as seriesregulator, and a couple of high voltage caps.??
Please mail me any kind of schematics and give me some help and hints about this project...
Yes, I have seen it a couple of times when I was browsing around the net, but it is fun to make and design these things, and I have all the parts I need for this kind of project. I just want to read som experiences from others.
Do you have a link, pdf, scan..? I would like to read it.
Hi
Yes, I have done this for some time, but now I want to make a real HV power supply instead of the HV transformer/variac method. I have several HV transformers from 500-2KV. The real supply will of cause have a 6,3V output on the same box.
It will be helpful if you can include some other supplies in the same box:
6.3V AC (with tappings for 4v if you want to use really vintage valves). A couple of tappings at + and - 15% will be useful to check if your design is unduly sensitive to emission and mains supply variations.
A negative low-current supply for grid bias. O - 10 v for signal valves or 0 - 30v for power valves. It may help to have several supplies available on potentiometers from one stabilised line, so you can test several stages at once. They may need to source or sink small currents, so a potentiometer is better than a stabiliser chip for these.
A second high voltage low-current supply for screened grids or beam plates. Again it should be potentiometer derived because it may have to sink current. A hefty rotary switch and a string of high wattage resistors is the way to go. A two-bank switch with staggered resistor chains and a separate rotary potentiometer connected between the wipers will give coarse and fine control if you need it. <
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It can either be connected across the main HT supply before the stabiliser or it can have a small supply of its own. It doesn't need to be particulary accurate, but it should be smoothed with a hefty electrolytic capacitor. If it uses a small dedicated supply, this can also be heavily smoothed and usefully brought out to another set of terminals for powering the earlier signal stages.
It helps to have the HT switchable independently of the LT, that way you don't have to keep switching the heaters off and on while you make adjustments (and you don't get tempted to save time by leaving the HT on while you fiddle). Use a big obvious switch - label it clearly - and have a large, bright, red panel lamp to indicate when the HT is on. Always try to work with one hand in your back pocket, you will reduce the risk of a shock across the chest.
*** All storage capacitors must discharge rapidly when the HT supply is cut - otherwise you will get some very nasty shocks.***
See if you can get hold of wireless constructors magazines of the 1950s or 1960s, they often had articles on HT and LT PSUs. Another source would be radio amateur handbooks of that era.
Get hold of the valve manufacturer's data books and read them - they will save you a lot of expensive trouble and anguish.
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Is that the one with the off/standby/on switch on the front? If so, never use it with transistor circuits. When you switch from standby to on, it overshoots about 80 volts!
Does the PS need to be SS? There are many bullet proof tubed designs.
And why go down to zero volts? That really complicates things & many practical regulated PS's are not that stable, zero to 100 volts. My own preference would be two supplies. That would be a zero to 150 SS & a 150 to 500 volt tubed version. That way one can do the biasing while the other handles the B+.
Either way it's actually the die temp that ultimately matters. Case temp simply factors in the junction to case thermal resistance making the calculation easier for the novice. If an insulating washer is used then you need to go back to die temp and add the washer's resistance in the thermal circuit.
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