I need a 45 volt DC power supply for a tube regenerative radio, but don't like the idea of using 5 9 volt batteries. I found a transformer I was thinking of using two in series, but I'm not sure how safe 45 volts is at 500 mA. The transformers are AC/AC so I'll also have to use some 1N4007 rectifiers. Transformer is Cat# M2860 at
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I'm going to use the 30 volt tap on one and 15 volt tap on the other and wire in series. If I also use a 4.5 or 6 volt transformer for the tube filament, what resistor value would I need to get it down to 2 volts. The tube is a # 30 type with 60 mA filament.
For the filament, as I recall the LM317 will go down to 1.5v, for your HT why not use a voltage doubler cct with the 30vac tranny ? Since the upper limit for the 317 would be above 30v you could use the one tranny.
I would like more info on this voltage doubler. As for the filament, will probably run it on one or two D cells, don't mind replacing them, and with only 60 mA current draw, will probably last quite a bit.
So I can use an LM317 chip powered from the 30 volts for the filament? How do I wire this up? Closest I can find is the LM317t which handling 1.5 amps. If I use a voltage doubler, the voltage would be around 60 volts. This radio wasn't cheap to buy, and I don't want to damage it with to much voltage. Perhaps my 1 amp 23 volt DC switch mode wall wart would be better instead of the transformer. It would be cheap, just install the voltage doubler circuit in a plastic box, with a DC plug at one end, and binding posts at the other.
Perhaps I can get another switch mode wall wart and wire the two in series, both set at 23 volts. That will provide 46 volts DC. I believe the one I already have is category # M9926 @
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Would probably need some sort of filtering to remove hum. I seem to remember this is done with a large value electrolytic cap across the secondary output.
I'd recommend that you do first try the 5 9V batteries, and some D cells with a resistor for the filament. This will be the most hum- free arrangement. Then when you build your supply you can compare the level of hum with the battery arrangement to give you a performance level to shoot for. One thing to make sure you do is put small (0.01 uF) capacitors across your rectifier diodes - otherwise when they go into and out of conduction they can generate 120 Hz RF noise.
Have you looked at the M0144 transformer? I don't think the taps you are proposing can be used in series. Your filament current needs a separate transformer.
Might be the best way to go. Hell, if the batteries last long`enough, I'll leave it like that. I can't see a one tube regen consuming too much current anyway.
"Dave.H" wrote in message news: snipped-for-privacy@s37g2000prg.googlegroups.com...
You might consider a switching boost power supply such as LT1268 which can provide a regulated 45 VDC supply from 3 volt batteries, which can also be your filament supply if you drop it down with a diode to 2.3 VDC. The LT1268 is $8 from
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but it will be cheaper in the long run than 5 9V batteries, and the additional parts are only a few dollars. You can also get less expensive switchers that might do the job, especially if you use an external MOSFET. The 3 volt supply can make gate drive tricky, but you could use a bipolar switch.
Other monolithic switchers that should work are LT1170HV, LT1070HV, LT1073, and LT1072HV. The LTspice circuit follows:
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