I finally received the unit pictured below and here's initial impressions.
Buying from Mastech was a good experience, but email that unit is in stock before purchasing as the website inventory count maybe inaccurate. Sean is very responsive to email; you'll get an answer < 1 hour. We've had several exchanges before payment. The website has some errs, but the picture of the device below is true.
It shipped via Fedex, from CA. It took a week to arrive to me.
It was a sealed box original from China. It was packed well, and interestingly the styrofoam mold was hand cut and assembled with glue to fit the unit.
I haven't had time to photograph anything, but build quality and design is
good for any design, but excellent given the cost.
The unit is about the size of a shoebox on its side.
The design is like an old IBM PC case, all sheet metal held down by screws. 5/6 sides are all metal walls, the front face is plastic attached to a metal frame. The machining, fit, knobs, buttons, jacks, paint and finish are all well made, like a good Heathkit circa 1980s, very solid feel. Plastic is thick and hefty, a dull off white finish.
Dials turn nicely, panel meters are evenly lit.
The manual is chinglish and not helpful. None of its advertised features, and more, are mentioned. Using it is fairly straightforward, and I am putting together what it does by reading other Mastech and the GWInstek manual. For example, it does not describe what the hi/lo amps switch does, the adjustment screw beneath the volt or ammeters, whether it had short circuit protection, or how to remove the ingeniously placed fuse holder.
The fan is strong, makes for noisy fan like sound. You can feel the suction from the vents cut into the sides of the unit, making for palpable airflow, exhausting from the rear. Older Mastech designs had a large heat sink in the rear which made the unit bulkier, so the fan makes the unit much more compact. The noisy isn't any more than a PC would make.
The output voltage/current is fairly stable after 3 hours of testing, no drift. The meters are at least accurate to 0.3%, but I haven't completed more thorough electronic testing, and follows later. Fine adjusts about 10% of coarse, so at 30 fine is 3, at 3 fine is 0.3 etc.,
Hi amps is 1.5-3 A, Lo is 0- 1.5 amps.
It will work down to 0 volts.
It has short circuit protection.
Constant voltage and current lights work when the modes engage.
Opening the case is easy. Sheet metal screws. Rubber feet screwed to bottom. The PC board is built like the photo from RC groups, clean, widely spaced, through hole parts typical of 1980s style design. Easy to fix if needed. My prelim scan confirms many easy to find generic parts. Well assembled, clean, good quality hand soldering. Wires cleaned routed and bunched. Nothing unsafe needed fixing.
Main transformer is laminated core. Full wave bridge is screwed into the metal floor to heat sink it and the leads are insulated with shrink wrap tubing. Main power transistors are bolted to an aluminum heatsink the size of the entire rear, and faces the fan.
In toto, very well made linear PSU. As mentioned earlier, well worth buying and modding as you see fit. You may not be able to get a replacement transformer if it blows, but its easy to fit a substitute in here. The overall look is very professional.
To follow: load regulation, drift under load tests, and more on DVM accuracy.
I purchased one, and should be able to examine the guts to describe it, in 2 weeks or so. But various older models have been dissected in other forums such as RC group. If you feel the regulator design is inadequate its design is simple and easy enough to modify.
If you total the costs of buying parts to build: dual LED DVM, transformer, casing, knobs, PCBs etc., I doubt you can match price nor obtain a polished look by buying a Mastech and modifying it as you see fit.
Although I cannot be dead certain, there are so many other PSU's that look, and spec-a-like the Mastech's to suggest the principle ODM provides PSU to other brand names, such as the low end Instek models, that suggests the fundamentals of Mastech's product are sound.
A $90 Mastech Model GDS-3030D versus an identical Model numbered Instek for $180 with similar power supply specs, but with differences such as handle, the single LED readout and in the manual, there are addition controls in the back of the Instek absent in the Mastech.
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