restorer-john
Grand Contributor
1) Sure. If I owned it already and it was working. Why not? In one of my systems I use an amplifier that was designed by Dave (and Ed Laurent) from the late 50s. It works fine. Pretty much stock (no new board design, however with new tubes and other discrete components)--the original stuff probably isn't going to work well, electrically). FWIW I owned both the Hitachi amplifer and Strickland's TNT 200. The latter was excellent at driving the rather difficult Acoustat lousdpeakers of the day. The Hitachi was less powerful, and succumbed to a Central Florida electrical storm one evening.
2) Erno designed Hafler's early amplifiers, so I did mention Hafler, just didn't use the name. Also, Jim Strickland (Acoustat) was responsible for later Hafler designs. Julius Futterman is said (by Harvey Rosenberg) to have been working out an idea to use MOSFETs for tube based amplifiers, and I believe that design was 'finished' by George Kaye.
3) I would never recommend a used amp over a new one. Unless you are able to fix it. Where are you going to get Hitachi MOSFETs now? Or Sony VFETs? As to current amps? To tell you the truth, I don't even know what 'high end' is supposed to mean anymore. @ShadowFiend mentoned Halcro. The Bascom King hybrid amp uses MOSFETs. I suppose those names are 'high end'. I'm sure their are others, but I don't follw that scene closely.
However, to be square, one must specify what MOSFETs one is talking about? What is available today? I'm sure someone like @restorer-john would know. But I don't.
For those who can 'hear' differences (I can't) the following is from an interview with Erno:
EB: So, we moved back to the States in 1978 and I worked for Dave again at the David Hafler Company. I designed the DH101 preamp and also the DH200 (Fig. 1) power amp, which was the first one to use MOSFETs in the US.
JD: These were the Hitachi lateral MOSFETs?
EB: Yes, for me these sound the best of all MOSFET types. At low bias they sound kind of soft, and come very close to tubes. They have relatively
low Gm but the negative tempco is a plus. Vertical types such as the Toshibas have higher Gm but a positive tempco, which makes it more difficult
to stabilize the quiescent conditions. They can sound quite good as well, especially in the bass department, although for full-range I would always
prefer the Hitachis. And the Hitachis can sound good with only 100mA, while the Toshibas would need at least
double that.
I don’t like the IR-type power MOSFETs, although they have a very high Gm. When I used them I had an extra identical device on the heatsink as
the bias regulator to keep the positive tempco under control. They measure well but they are not my favorite for sound quality, unless you go to very high bias currents or other topologies such as Nelson Pass is using.
The Hitachis are only available on the secondary market and only then, through pulls from big commercial/PA amps that used them through the 1980s. You can pick up amps that use them for very little money and maybe get a few dozen or more depending on the models. I picked up a 200+200W Australian built PA amp with 8 Hitachis in it for $5, just for the MOSFETs to fix a big Perreaux.
The Toshibas used in the amplifiers above are NLA, but my Japanese supplier has plenty of NOS. The Exicons were good, but again, NLA. But I've got a ton of most of the MOSFETs I'll ever need I think.