Re: Roister Pb-150 Subwoofer repaired, how to prevent from failing again?
OK, my turn.
Upgrade the drivers, Q47/48. Final gain drops at high output current; driver not only needs to be robust, but also keep its gain up so the previous stages stay linear.
The C5200/A1943 should be driven with something like a MJE15032/33, 15030/31 , or 15028/29 comp pair.
The 028/029 will work since this amp runs ~51v rails; use what's easy to get.
Make sure you transpose the leads; TO-220 is different vs TO-92.
And be sure to put NPN->NPN & PNP->PNP.
These won't need heatsinking beyond the tab.Your PCB is silkscreened for bigger drivers- look close, they cheaped out.
Don't worry about TO-126 for drivers- go right to TO-220.
TO-92 or TO-92(L) is absurd- amazing it lasted this long!
Q45/46 are DC detect monitors, one for each polarity. These kill drive to relay driver when triggered. Pretty low duty, so conductive/corrosive glue or borderline/"second" parts likely.
Q49/50 should be replaced with BD139/140. Make sure NPN->NPN & PNP->PNP and you transpose the leads! Otherwise, you're sending +/-51v into the opamps!

Change the two 47u/25v, across the zeners for the +/-15 regs, to 100u/25v. Make the reference for the reg better vs extra filtering "after the fact."
Change C67 to 47u/50v, 105c, PW, HE, FC, etc. if you haven't already.
Change C66 to 22u/50v, also PW, HE, FC, etc.
If the main filters have been in this long, they'll keep formed at the higher voltage.
Electros are initially formed at a bit more than rated voltage; yours will likely tolerate 54-56v.
The toroidal transformer can/should keep the rails up better than an E/I.
Should make an easy 150w/4ohms, especially with 230 vs 220 in.
Possibly 180-200w peaks if "pushed," but there's only one set of finals; push it only with an external fan on that heatsink.
Don't worry about opamp "rolling," 4558s are just fine in a sub, and besides, those are JRC!

Good luck and "play it loud!"
OK, my turn.
Upgrade the drivers, Q47/48. Final gain drops at high output current; driver not only needs to be robust, but also keep its gain up so the previous stages stay linear.
The C5200/A1943 should be driven with something like a MJE15032/33, 15030/31 , or 15028/29 comp pair.
The 028/029 will work since this amp runs ~51v rails; use what's easy to get.
Make sure you transpose the leads; TO-220 is different vs TO-92.
And be sure to put NPN->NPN & PNP->PNP.
These won't need heatsinking beyond the tab.Your PCB is silkscreened for bigger drivers- look close, they cheaped out.

Don't worry about TO-126 for drivers- go right to TO-220.
TO-92 or TO-92(L) is absurd- amazing it lasted this long!

Q45/46 are DC detect monitors, one for each polarity. These kill drive to relay driver when triggered. Pretty low duty, so conductive/corrosive glue or borderline/"second" parts likely.
Q49/50 should be replaced with BD139/140. Make sure NPN->NPN & PNP->PNP and you transpose the leads! Otherwise, you're sending +/-51v into the opamps!

Change the two 47u/25v, across the zeners for the +/-15 regs, to 100u/25v. Make the reference for the reg better vs extra filtering "after the fact."

Change C67 to 47u/50v, 105c, PW, HE, FC, etc. if you haven't already.
Change C66 to 22u/50v, also PW, HE, FC, etc.
If the main filters have been in this long, they'll keep formed at the higher voltage.
Electros are initially formed at a bit more than rated voltage; yours will likely tolerate 54-56v.
The toroidal transformer can/should keep the rails up better than an E/I.
Should make an easy 150w/4ohms, especially with 230 vs 220 in.
Possibly 180-200w peaks if "pushed," but there's only one set of finals; push it only with an external fan on that heatsink.
Don't worry about opamp "rolling," 4558s are just fine in a sub, and besides, those are JRC!

Good luck and "play it loud!"

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