Sony TA-N88B recap and parts selection advice

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#21
ilimzn said:
...getting MOSFETs with such a low input capacitance ... is pretty much impossible.
...fastest switching semiconductor built in silicon...
... about 200pF Cgs...
...Usually this is a switch for radar pulse generation...
Rebuilding the N88 with MOSFET outputs is a HUGE mod.
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200pF! That's nice!!!
As you explained, that makes them very fast indeed.
Somewhere in the eighties, I cooperated in building a submarine sonar (depth-tracking for ships in nasty waters) based on mosfets. During pulsebursts, the rest of the electronics (signal and control) were 'shorted' with opencollector nand gates to avoid saturation and other cruel things.
Still, I would rather use vfets as triodes instead as switches.
A N88 with mosfets as a concept of thinking. Of couse & agreed almost impossible to achieve.
 
#27
Those J28's & K82's are hardly to find, if you find some on ebay, expect to get freshly stamped rubbish. Unfortunately there is no NOS available, I heard that the las units were sold from Sony to Nelson Pass, as he had an Amp-project with those jewels. Ask Nelson Pass, from the restoration precess of mey TA-N88b I know that he has still some, and 2 years ago, he was able to find certain gradings. Send him an email. Good luck! this amp is tricky, do not try to repair it by only exchanging defect parts, think in advance, if your power supply blows up, it may kill your VFETs. That was my big problem.
 
#29
V FETish
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I lol'd


Those J28's & K82's are hardly to find, if you find some on ebay, expect to get freshly stamped rubbish. Unfortunately there is no NOS available, I heard that the las units were sold from Sony to Nelson Pass, as he had an Amp-project with those jewels. Ask Nelson Pass, from the restoration precess of mey TA-N88b I know that he has still some, and 2 years ago, he was able to find certain gradings. Send him an email. Good luck! this amp is tricky, do not try to repair it by only exchanging defect parts, think in advance, if your power supply blows up, it may kill your VFETs. That was my big problem.
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Thank you for the reply and insight. Im waiting to hear back about a source for some vfets if that falls through I will try Nelson. I will also post updates as I start to work on the amp again. I would love to hear more details about what you did for your restoration.
 
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