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my new psu
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Hi all, I have just brought this psu,
its o-30v 0-1a,its made of discrete components with no ic's, its transfo has a center tap then +50v,+40v/-50v+-40v taps with a seperate 6.3v winding , the main voltage pot is a 1k with just the center and one outer leg used,its 1k at max volts,would it be possible to mod this for say 2amps and 70 ish volts output? would anyone have any ideas ie schematics etc,or an explanation of its circcuit topolagy,it has a wirewound resistor of 1 ohm,i assume that is a current sense resistor,i have uploaded some pics of it in the photos section called my psu,cheers in advance 73 Paul de m3vuv. |
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On Saturday 30 November 2024 04:29:03 pm paul larner via groups.io wrote:
the main voltage pot is a 1k with just the center and one outer leg used,In a situation like this, it's really best to tie the unused leg to the center one. The reason for this is if there's any intermittent contact, the effective resistance goes from wherever it's set to effectively an open circuit, where if you have the unused end tied to the center then an intermittent contact will at worst give you maximum resistance. This goes for trimpots, too. It's common practice, or should be. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin |
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?Has anyone have any ideas on this? On Sun, Dec 1, 2024 at 6:20?AM paul larner via <quadzillatech=[email protected]> wrote:
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Probably not. Max voltage typically set by regulator itself, inconjunction with raw DC being supplied off transformer.
If you find that output isn't what it should be, look at rectifiers and filter circuitry between transformer and regulator input. In addition, look at heatsink on regulator (s). Excess ripple (leaky rectifier, cap) can cause ripple rejection to limit output of regulator(s). If heatsink is loose, or compound dried out, that can cause regulator to run hotter and possibly reduce output. For a higher voltage, at near same power, consider use of single ended or variable boost converter. ~SD |
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Found your pics in photo section. Labeling on transformer yields 1A across all windings, likely because
they are all a common center tap. I would expect the 6.3v winding to be around 3Amps? Is there just the single 6.3, or is it split into 5 / 6.3? In a couple of the pics, 20241129_160556.jpg and 20241129_152617.jpg, the transformer appears to have been stressed. Appears that there is some discoloration already, though may just be a light artififact when pic was taken. Bear in mind that that transformer has a lot of windings on it, and 1 intended (main) to be used at a time. You draw double the current, and you may end up saturating the core. Not good. You might get away with drawing greater current at a lower voltage winding, but looks like you are already connected to the 45v tag. Higher Voltage? No way would I do that as the supply sits. Pass transistors exhibit wear on cases, hope surface of the mica insulators is not compromised. 1 transistor likely for voltage, other for current. If supply set for 5, and transformer is connected at 45, with a 1A draw, the voltage pass transistor is going to be dissipating ((45-5)x1) 45 watts of heat. Doubling that to 2amps and you likely are going way outside design specs and looking at a much higher junction temperature in the transistor. Plus, you don't know how close the main caps and such are in relation to working voltage rating compared to actual voltage. If a diode has become 'leaky' and allows excessive ripple to pass, working voltage rating may be exceeded. Similar for the (National Semi?) old plastic pill style transistors. Had a bit of a time dating that power supply, was going to peg it around 1978 to 1980 based on component and wiring styles. But, I saw that one of the meters has a 0272 date code, translating to 2nd week of 1972 if the meter is original. Ultimately it comes down to are you willing to stress the supply given its age by exceeding ratings that are present on at least some of the components? If it were me, that would be a NO until I can slowly check it out. I am quite curious, as to what is connected to the 6.3vac windings? Are they supplying the heater for a valve rectifier? If so, got a part number? The meters are likely going to be a 50uA moving coil variety. Have you considered scrapping the internals, then retrofit with off the shelf variable Boost / Buck regulator supplied by a larger transformer, possibly a 100w laptop power supply (20v @ 5A)? I would think would be much tighter on output than a supply that is 52 years old, despite its brethren (like 5002) having excellent characteristics. ~SD |
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thanks,it has no valves in it,,so dont?know about the 6.3v windings,what is the 5002 you mention?,cheers paul. On Fri, Dec 6, 2024 at 5:59?AM SheldonD via <68696465=[email protected]> wrote: Found your pics in photo section. Labeling on transformer yields 1A across all windings, likely because |
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The 5020 is s Zaurie power supply model that was heavily pushed / reviewed in early 1970s. I got mine in 1978, used, from a garage sale. Heavily abused, and if memory serves, used a selenium stack for rectifiers. May be getting mixed up with another supply. Hard to remember 40+ years ago.
How many 6.3 windings are present on transformer? Mine had 3, i think, and were used to make an aux high voltage output. ~SD |
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wn4isx
If the power supply in question has selenium rectifiers they need to be changed.
They weren't great to begin with, very high internal impedance, and they don't age well.
If the paint protecting the selenium crinkles from age or heat, the selenium will degrade!
Replace with silicon rated at 4 times the current and at least 2 times the voltage.
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