Sony VFET...tragic...

[EchoWars]

Nice little 4650 integrated, with one dead 2SK60.

What's the chance of finding one?

[jocko_nc]

Echowars:

I know a dumpy pawn shop that has an allegedly-working 4650. I could go get it and pass it along for cost. I'm thinking $50.00. Is it worth for parts? I know VFET's are increasingly rare, is this a good find?

I passed on buying the unit a while back. If I could make someone else's day, that would be cool.

jocko

[paulb]

I think these are all toasted too, although I haven't tested them.

[EchoWars]

Do you know how to test them? I'd love to bring this amp back to life...

[anatech]

Hi Glenn,
They should have high impedance between the gate and other electrodes. Put an ohmmeter probe (low voltage) between source and gate. Measure the drain - source resistance. Reverse the charge from gate to source and measure drain - source again. One way should be low impedance, the other open or high impedance.

Quick and easy with nothing but an ohmmeter.

-Chris

[EchoWars]

I know how to check them...since he hadn't done so yet, I was wondering if he did...

[anatech]

Hi Glenn,

Yes, I know...... but you did ask.

-Chris

[EchoWars]

Rgr that...

I HATE tossing anything onto the junk pile for want of one bloody transistor. There's just something very wrong about it.

[ilimzn]

Originally posted by anatech
Hi Glenn,
They should have high impedance between the gate and other electrodes. Put an ohmmeter probe (low voltage) between source and gate. Measure the drain - source resistance. Reverse the charge from gate to source and measure drain - source again. One way should be low impedance, the other open or high impedance.
Quick and easy with nothing but an ohmmeter.
-Chris

Chris, this would be true for MOSFETs, these are VFETs.
gate to drain or source will show a diode one way, open the other. Drain to source will show about 1 ohm, perhaps a bit more if gate-drain or gate-source were polarised in the depletion direction by the previous measurements. VFETs have a very high pinch voltage, plus have rather interesting modes of failure, so as simple as these measurements are, they are not conclusive, though.

[paulb]

Originally posted by ilimzn

.. VFETs have a very high pinch voltage, plus have rather interesting modes of failure, so as simple as these measurements are, they are not conclusive, though.

Right. So I haven't tested them. If somebody can dig up a datasheet I'll have a go at it.
I can contact the owner and see if he wants to give them away. The Sony amp I got them from now has an LM3886 amp in its place. The amp layout was such that it was pretty simple to drop it in place of the original boards. Runs much cooler now.