Hello People, I am repairing a Crown model CSL800 power amplifier, it uses a 100Vdc power supply with floating ground. I can't get data on the original output transistors (4 per rail), although I saw on some forums that they have used MJ15025 and MJ15025 as replacements. Unfortunately, in my country, it is very difficult to obtain original transistors, I decided to buy some and when I received them, visually they already seemed like bad copies. I measured the breaking Vce and they barely reach 140V. My query is as follows, I have a sufficient quantity of MJ15003 and 15004, of good and proven origin, and although these are 140V against the 200V of the 15024/25, as I see it, in the SOA curves it could work well, what's more, the 15003/4 looks a bit better. If I consider an increase in VCC of 20%, I still have a safety margin. Any suggestion, much appreciated.
I’d want to see the schematic or measure things myself to confirm it’s only 100 volts rail to rail before using 15003/4. 15003/4 are normally suitable for +/-50 volt operation if that’s what’s really going on.
Perhaps if you use a distributor with a warehouse in country you can access real ON semi MJ15024/25 . Then pick them up in capital city yourself, don't use a freight service. Pilfering used to happen here with the biggest package delivery service before they put cameras on all the trucks. Bad things happen at the border. For an individual, the government can always delay your court case until you run out of money and go away. A business like farnell or RS has to come some arrangement with the border guards to get their inventory in regularly. The cost may be less than 100% of the value of the shipment.
I would attempt to get real MJ15024/5, but if it’s a choice between fake 15024 and real 15003 I would take the real 15003. This circuit is only running on +/-51 volts. It’s the old grounded bridge topology - Crown’s old trick for getting around the SOA limitations when making high power amps. 15003/4 are suitable it this circuit. The original type might have even been the 2N5630/6030 which were used in the latest rev of the DC300A when RCA dropped the old hometaxial version of the 2N3773. And those had at least two viable sources (Motorola and Fairchild for sure - maybe more) back in the old days.