MOSFET magic; a wonderful sounding amplifier. Superb build quality and seems to be reliable. MOSFET amplifiers usually run warm to very warm, They sound better if you switch on and let them warm up for... 10 minutes, or sound improves after a short period of listening. I absolutely love mine. They have 2 (complimentary) MOSFETs per channel, 2sj50/2sk135 pair. Power supply smoothing capacitors were originally 10? small 2000 uf? capacitors (5 in parallel on each side; positive/negative) which gives a very low ESR, so supposedly a better design? I have seen an example with 4 larger capacitors that look as if they were installed from new. See RHS of first picture. The build quality is similar to the earlier A150 model but the component layout is quite different, a completely different circuit board so more than a simple update; also the whole cabinet is larger, wider with the newer A150b.
Update: Time for a little TLC on my A150b, needs new capacitors as during a routine inspection I notice a few with slightly bulging tops! So the mostly 100uf capacitors used in the individual power supply were replaced with high quality Panasonic types. When I originally got this amplifier it was faulty...not working at all. I spent some time diagnosing the problem ...I tried to ignore the possibility of a failed output device, they are MOSFETS and at the time very difficult to buy new, indeed new original Hitachi ones were no longer available, they are also a little tricky to test in circuit unless completely shorted (these weren't)... anyway there came a point where I had to agree that at least one output device was faulty and so removed the two offending in the faulty channel I did determine one was likely faulty (I had no transistor tester at this time I now use a Peak Tester) I managed to find new ones available of another (two) brands, i.e. they had a complementary pair but not by the same maker! I ordered them and put them in place and bingo all was working as it should. Whew! So while replacing the capacitors I decided to also replace the two off brand MOSFET outputs with salvaged Hitachi one that I had since come across. How you ask: well they were widely used in many amplifiers in NZ as MOSFET devices were being marketed as a new product and easier to design with. Fewer components are needed as the MOSFET needs less thermal protection due to a positive temperature coefficient, resistance goes up with heat, so they are less able to thermally "runaway"; c.f. with BJT's). MOSFETS were widely used in Public Address and sound reinforcement amplifiers as well as Hifi amplifiers so I have over time managed to salvage a few pairs from some PA amplifiers, and those are what I have used for the Mclaren A150b! about time I could have done this several years ago.
NO: It's not for sale, this amplifier is a keeper of all keepers! It's FABULOUS.