"This V/A 200 (Valfet, (valve & mosfet)) high quality Hi-Fi audio amplifier was brought to me buy a guy (Dave) from Grimsby, UK after a pre-arranged phone call. Dave explained to me that this was one of a pair of these he had and used on his home Hi-Fi system. He had previously hocked this around seven tech men (of whom one had had it for 5 weeks) and all of them didn't, couldn't, or just simply were not interested in, sorting it out! The fact it contained just one valve (tube) was the reason he contacted me via my web-site.
Though it does have the one valve (ECC83) as the main input amplifier, in reality this amp is really, mainly transistor/mosfet. I don't really like doing these things as I find them "no fun". Nevertheless, Dave was in "dire straights" with this so I offered to help him out.
Whilst the performance of this amp is superb, its designer could do with looking down the barrel of a Colt 45!! It is of no wonder that all the other tech guys didn't want to have anything to do with it as it is a technicians night-mare, due to the physical way in which it has been designed.
Once getting to the bottom of things it turned out that one of the two bridge rectifiers had gone short. This had caused a massive EMF flash/surge which not only had damaged transistors/components on the drive board, but had also caused one of the "P" channel 2SJ50's to go partially short! In a situation like this it is not worth risking the rest of the output devices, so after repair/replacement of the bridge rectifier, the drive transistors, and associated components, in went a complete new set of output devices - four 2SJ50 and four 2SK135's. (The original Hitachi devises are no longer manufactured, but Semi-Lab of Leicestershire, UK do a suitable replacement now.)
After a full check up and test it came back to life with a perfect 200 watts into 8 ohms.
Whilst I wanted to show this on my web-site, on the other hand please PLEASE...... unless you have tried every other tech-man in the country to no avail and are really stuck....... please don't bombard me with trany stuff !!
Cheers for looking, John"