As you saw in my later posting its not all good, it does have its warts as well, big ones. It's as bd139 pointed out, if they only spent a little more money putting it together safely, it would be spot on. If it put another £2 on the price, it would still be a good bargain and would compare favourably against the big Western names costing many more times the price. Why oh why do do these companies not see the errors they make and put it right. Who knows what heights they could reach if only they paid a bit more attention to the what the global market demands in terms of safety?
This is the frustrating bit. Some of the designs are spot on bar a few mistakes and cost cutting. Excuse the rant here but it annoyed me...
One of the really annoying things is the cheap Mastech power supplies. When they work they are absolutely spot on bits of kit, up there with even HP and TTi believe it or not on the transient and noise front. Problem is that every part is pushed to the line if not slightly past it failure is inevitable eventually. I had an HY1803D a few years ago. 3A out, 18V, fully linear. CV/CC mode. Great for radios. Noise was good. Transient response was good. Really cheap bit of kit - was £50 or so from Rapid.
That was until suddenly I got 27V out of it which ruined my day at the time as I was playing around with sensitive low Vce RF transistors which promptly ejected their souls. So what happened? Well they use a relay to switch taps on the primary transformer so that the main power transistor doesn't have to dissipate to much power which keeps VCE down as VCE*IC=PD. However the damn relay fails after about 6 months and then the entire thing starts burning off a lot of power. This blows the arse out of the hooky 2n3055 they use as the main transistor and then it goes VCE short so you get the full voltage out.
Comparing the implementations between a £50 Mastech and a £627 Keysight/HP supply (yes thats full retail difference) ...
Mastech. Simple comparator using a left over LM324 and transistor to sample the output voltage and switch the relay on and off to select taps if it goes more than half of the power supply range. Blows up after 6 months.
HP. Simple comparator using a left over LM393 and a transistor to sample the output voltage and switch a couple of SCRs on and off to select taps if it goes more than half of the power supply range. Still works after 23 years.
Hang on a minute? That HP one is entirely solid state! Nothing mechanical to fail! How much does an SCR cost? sweet f-all! There's no patent on this idea, not that anyone cares in China. Price differential is at most half a dollar.
The BOM cost of the HP and the Mastech are actually about the same per channel. There's bugger all in either of them. Just some better quality pots and some marginally better quality components in the HP.
So close but so far
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
... and this is frustrating because I'd rather spent the price of a Mastech power supply than an HP one! In fact despite the explosion, the mastech one is easier to maintain. Also the comedy bit is the metering on the mastech is less crap.
Perhaps I should build an aftermarket "mastech power supply engine" which you can just rip the one out in it and stick a decent one in.