Hi,
Always thankful for everyone's time and interest. I have received a part that I'm not sure is genuine. Can a part that tests as Darlington with Rshunt and w/ Protection Diode features be used in place of a standard TO-3 device? In my application - class AB power amp, where only the PNP's are Darlington - I think not, because the Vbe is double on the Darlington devices, so class AB signal switching won't line up properly.
I am repairing a Pioneer SX-1250, which has been blowing the main 12A fuse on startup. After testing the output devices, one bank of TO-3's has been found completely shorted. There are 4x total TO-3 devices per side: Parallel pairs. Neither side appears original. The good side has been tested with sig/scope and music, by disconnecting the power supply and driver board for the bad side. As it stands now, the working good side has 2SD555 and 2SB600 pairs (NPN and PNP, respectively), while the blown side has NTE87 and NTE88.
I have purchased 5 pairs of 2SD555 and 2SB600 parts from a vendor on eBay. The 2SB600's are the ones that test as Darlingtons, and so these are the one's I suspect to be questionable, as the datasheet for this part does not show either a Darlington schematic or mention of this arrangement. Tonight I pulled the known, good 2SB600's from the working side and they tested as standard ~.602 Vbe.
Equipment used for testing: Peak Atlas DCA75.
*Since we're on the shared topic of transistor matching, can I get a quick confirmation that Beta/Hfe testing is of primary importance when matching individual/solo (stereo) pairs of preamp/power devices, and Vbe testing is primarily important when matching parallel pairs? Thanks.
Always thankful for everyone's time and interest. I have received a part that I'm not sure is genuine. Can a part that tests as Darlington with Rshunt and w/ Protection Diode features be used in place of a standard TO-3 device? In my application - class AB power amp, where only the PNP's are Darlington - I think not, because the Vbe is double on the Darlington devices, so class AB signal switching won't line up properly.
I am repairing a Pioneer SX-1250, which has been blowing the main 12A fuse on startup. After testing the output devices, one bank of TO-3's has been found completely shorted. There are 4x total TO-3 devices per side: Parallel pairs. Neither side appears original. The good side has been tested with sig/scope and music, by disconnecting the power supply and driver board for the bad side. As it stands now, the working good side has 2SD555 and 2SB600 pairs (NPN and PNP, respectively), while the blown side has NTE87 and NTE88.
I have purchased 5 pairs of 2SD555 and 2SB600 parts from a vendor on eBay. The 2SB600's are the ones that test as Darlingtons, and so these are the one's I suspect to be questionable, as the datasheet for this part does not show either a Darlington schematic or mention of this arrangement. Tonight I pulled the known, good 2SB600's from the working side and they tested as standard ~.602 Vbe.
Equipment used for testing: Peak Atlas DCA75.
*Since we're on the shared topic of transistor matching, can I get a quick confirmation that Beta/Hfe testing is of primary importance when matching individual/solo (stereo) pairs of preamp/power devices, and Vbe testing is primarily important when matching parallel pairs? Thanks.
Definitely fake. I would also suspect the 2SD555 as well. Demand your money back. Ebay sellers dont always sell genuine parts.
Mj15024 and 15025 also MJL 21194 and 21195 will work fine and not forget to readjust Bias
Dont buy fakes
Dont buy fakes
Vbe matching is most important for matching the BIAS at idle. The closer they are the closer you get. If the amp uses 0.22 ohm or higher emitter resistors, units from the same batch will generally be close enough to share current properly under LOAD even if bias is off by a couple mA at idle.
Matching hFE is important IF the amp is capable of extremely low (.000x %) distortion. hFE differences will show up and distortion may not get that low. No-feedback amps can also be sensitive to hFE differences between the two halves. With amps that use global feedback and are only capable of the typical .05%, hFE differences will be swamped and you’ll never notice whether the outputs are matched or not. And amps with EF3 output stages are less sensitive to hFE, matching, or anything else except temperature. In those cases, use stock ON semi MJ2119x and be happy.
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