Hello all,
I've read most of the posts I've found about this amp and power transistor matching in general. I bought this ARC D100B on ebay (paid more for shipping than the amp itself) and I'm re-repairing a lot of previous repairs and shorted transistors. I'm replacing them all and have purchased enough OnSemi MJ15024/25 to get Vbe-matched groups for the outputs but I'm having problems with the drivers. Based on the topology I would guess that these need to be gain matched pairs rather than Vbe matched since they're not paralleled. If I have this wrong, please let me know. I'm trying to use MJ21195/96 and while I can get some decent Vbe and gain groupings within the NPN or PNP lots, all the gains are higher for the PNP lot than for the NPNs. My matching PNP groupings were about hFE 115 where the NPNs are about 98. This is measuring Ic/Ib at Ic=85mA, 550mA, and 1500mA. Vbe between them is about 10% higher with the PNPs. Any guidance is appreciated...
Questions:
Matching? Vbe? hFE? Both? NPN=PNP? Will it matter to have the NPNs and PNPs this far apart in gain?
schematic excerpt is attached, whole thing is on the arcdb.ws site
Thanks in advance!
Russ
I've read most of the posts I've found about this amp and power transistor matching in general. I bought this ARC D100B on ebay (paid more for shipping than the amp itself) and I'm re-repairing a lot of previous repairs and shorted transistors. I'm replacing them all and have purchased enough OnSemi MJ15024/25 to get Vbe-matched groups for the outputs but I'm having problems with the drivers. Based on the topology I would guess that these need to be gain matched pairs rather than Vbe matched since they're not paralleled. If I have this wrong, please let me know. I'm trying to use MJ21195/96 and while I can get some decent Vbe and gain groupings within the NPN or PNP lots, all the gains are higher for the PNP lot than for the NPNs. My matching PNP groupings were about hFE 115 where the NPNs are about 98. This is measuring Ic/Ib at Ic=85mA, 550mA, and 1500mA. Vbe between them is about 10% higher with the PNPs. Any guidance is appreciated...
Questions:
Matching? Vbe? hFE? Both? NPN=PNP? Will it matter to have the NPNs and PNPs this far apart in gain?
schematic excerpt is attached, whole thing is on the arcdb.ws site
Thanks in advance!
Russ
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After more researching on this, I think I'll just go with what I have... Based on the circuit, the PNP drivers are in front of the NPN output group so if one type is inherently higher in hFE than the other than this should help even the symmetry out and besides, the numbers are fairly close anyway based on some other posts I've seen.
I'm also replacing all the emitter resistors with 1% noninductively wound wirewounds since there were some that were out of spec. Note that the schematic shows 1 watt and the parts list shows 2 watts but based on the size of the originals these appear to be 3 watts.
Russ
I'm also replacing all the emitter resistors with 1% noninductively wound wirewounds since there were some that were out of spec. Note that the schematic shows 1 watt and the parts list shows 2 watts but based on the size of the originals these appear to be 3 watts.
Russ
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