I posted a thread a bit ago, asking about replacements for these outputs. I was given a stack of amplifiers that use these outputs. They stopped working, and the person to own them took them to a repair shop and the repair shop refuse to work on them since they couldn’t get parts for them. So he gave them to me. I thought for sure that it would have all shorted outputs, then I would at least have big transformers, and heatsinks if I parted them out. Well, I pulled all 12 mosfets from the first amp and not one was shorted, but they did measure differently on my Peak Atlas DCA75. Some measured as Enchantment mosfets and some as depletion mosfets, yet the specs the meter was giving me was very similar. There was no rhyme or reason as to where the depletion mosfets were. Here is an example, I pulled the 3 2SJ56 from one’s channel and here is how they measured.
The two with the E above them measure at Enchantment and the one with the D above it, well you know. You can see that the measurements the meter gave me are all right in line with the others. Is that just an artifact of the mosfet interacting with the meter? Are they perfectly fine to use?
Thank you,
Dan
The two with the E above them measure at Enchantment and the one with the D above it, well you know. You can see that the measurements the meter gave me are all right in line with the others. Is that just an artifact of the mosfet interacting with the meter? Are they perfectly fine to use?
Thank you,
Dan
Dear Dan,
These J56 measurements seem to correspond with the hitachi datasheet I found. They should all be enhancement. The one indicated as depletion just seems to have lower Vgs.
The last row confuses me though. Should that be Vds being 8.0V instead of Vgs? Vgs of 8V should yield 5 to 10 amps. If not, they might be fried.
I would test those Pchannel mosfets by configuring them as current sinks using a pnp to control the gates. Nice find. They appear to be lateral mosfets which aint cheep these days. Hope they work.
Cheers,
Ruben
These J56 measurements seem to correspond with the hitachi datasheet I found. They should all be enhancement. The one indicated as depletion just seems to have lower Vgs.
The last row confuses me though. Should that be Vds being 8.0V instead of Vgs? Vgs of 8V should yield 5 to 10 amps. If not, they might be fried.
I would test those Pchannel mosfets by configuring them as current sinks using a pnp to control the gates. Nice find. They appear to be lateral mosfets which aint cheep these days. Hope they work.
Cheers,
Ruben
Thank you, that’s good to hear that it looks like they fall in line with the spec sheet. Just found it odd that they were being listed as different devices on the tester. I’m sure the last row is Vds, I probably just wrote it down wrong.
I’ll have to look into that test method you mentioned. Yeah it is a pretty cool find, I got 10 of these amps, hopefully all 120 of the mosfets are good.
Dan
Depends if you have a lab supply and some experience. I killed some transistors by connecting them the wrong way. Would be a shame if you killed some in testing. I think you can probably trust your DCA75 to see if theyre broken or not.
Anyhow I recently used something like this to match for Vgs:
If you indeed use current sources to test tripple or quadrouple check all connections.
Even better is using an opamp:
Much cheers,
Ruben
Anyhow I recently used something like this to match for Vgs:
If you indeed use current sources to test tripple or quadrouple check all connections.
Even better is using an opamp:
Much cheers,
Ruben
The measurement is of on-resistance, not maxmium Id. I.e. the FET is behaving as a resistor in the triode-region, not at saturation (pinch-off).
Its best to measure power devices at the power levels they are designed for, not at 1mA, since that's not necessarily going to spot faulty devices.
Alas high-power curve tracers are not cheap and plentiful!
When we designed the DH-220c amplifier, Bob wrote up a paper on testing and verifying the mosfets
Look at Bobs web site cordellaudio.com under power amplifier design
Look at Bobs web site cordellaudio.com under power amplifier design
