HexFETs would be a different world and you'd need to think about several changes, especially biasing mechanism. This would be a head scratcher with a little hifi amp, let alone a monster that has 86V rails... I say choose life.
You can scour Ebay for broken amps that used laterals. There are some pretty cheap ones (Soundcraftsman, is that one?) out there. Obviously, you'd need the variant that can take the voltage...
edited, as I posted a link to some for sale, but I do not think they will work as your rails are too high
You can scour Ebay for broken amps that used laterals. There are some pretty cheap ones (Soundcraftsman, is that one?) out there. Obviously, you'd need the variant that can take the voltage...
edited, as I posted a link to some for sale, but I do not think they will work as your rails are too high
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That's a very good idea.
Another option I found would be getting used components recovered from old boards, I have tried this method before with 2sc5200/2sa1943 and 2sc3281/2sa1302 and they turned out to be authentic (I even opened a few up to inspect the die).
@Mimiragon I would not buy used J162/K1058 at that price, you can get new Exicon 10N20/10P20 for the same price.
If you change to plastic package Lat-FETs, be aware that stability could take a hit. Lat-FET amps can be very picky about impedances around the Source connections - as well as capacitance around the gate wiring.
That's a very useful piece of information, but the original are indeed plastic lat-fets, I posted a picture of the amplifier a few posts ago in this thread.
After a few measurement on the working unit, the factory values of the current are
V+ Channel 1: 0.6A
V- Channel 1: 0.6A
V+ Channel 2: 0.55A
V- Channel 2: 0.55A
and they slightly increase with time.
The heatsink gets warm very quickly. I haven't tried for extended periods of time.
(Each channel has 4 pairs of 2sk1058/2sj162)
V+ Channel 1: 0.6A
V- Channel 1: 0.6A
V+ Channel 2: 0.55A
V- Channel 2: 0.55A
and they slightly increase with time.
The heatsink gets warm very quickly. I haven't tried for extended periods of time.
(Each channel has 4 pairs of 2sk1058/2sj162)
@thermionic @twister1264 @jacques antoine
Just an update on the situation, both amps have been repaired and they are in perfectly working condition now.
There were only 2 busted mosfets in total so I ended up getting a pair of the used ones for 10$.
The bias current has been adjusted to 400mA per rail on each channel, (since the factory adjustment was well above 600mA) the temperature stays close to 45-50 degrees with fans at minimum, no sign of distortion from 5Hz to 25kHz. Thank you everyone for the help and for the Hitachi application manual data.
Just an update on the situation, both amps have been repaired and they are in perfectly working condition now.
There were only 2 busted mosfets in total so I ended up getting a pair of the used ones for 10$.
The bias current has been adjusted to 400mA per rail on each channel, (since the factory adjustment was well above 600mA) the temperature stays close to 45-50 degrees with fans at minimum, no sign of distortion from 5Hz to 25kHz. Thank you everyone for the help and for the Hitachi application manual data.