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It is a well-known construction of laboratory power supply 0-30V 0-3A from: LINK. In this version, two identical separated galvanic power supply modules were used. Transformer is rewound Zatra TS 200/0412. Two 24V and four 5V windings to power the meters were wound. Meters work just after assembling, you only have to select the divider for ammeter. The accuracy of the power measure is up to 0,01A and drop on resistor R7 is measured. When the power supply is unloaded, voltage of about 4mV is present on it, but it does not affect the meter reading. Power transistor is 2N3055 from an old guitar amplifier. Tunnel cooling was made of two computer fans powered from a separate transformer. Fans were assembled at the end of construction, so there is no additional winding wound to the main transformer. Temporarily, cooling is powered directly from 12V, but you can add a temperature controller. The bottom cover is plywood reinforced with slats under the transformer and heat sinks. The front is made of thick plastic, screwed. Holes for the displays were cut with a saw blade and smoothed with a file.
Link to original thread (useful attachment) – Zasilacz dwukanałowy 0-30V 0-3A.