Punch Line First: I am starting this thread to elicit input from interested members, if there are any, about the 'best' option for replacing and/or updating output transistors on vintage Germanium based audio products.


I was given a JBL SE401 as a 'gift.' I spent a lot of time during 2019 'restoring' it. I was fortunate to have had a lot of help learning how to do that from several gurus. I heartily thank them. It may lead to another thread.


I started out 'lucky' that all of the original transistors tested 'good'. When I finished, a month ago, it worked, sounded and tested OK. I listed the SE401 on eBay.


Sadly, I continued testing with Ch B of the SE401. The original 'protection circuit' consisted of four self-resetting circuit breakers ['CB'] and a fuse. When two of the CB 'lit up' (who knew?) I guessed that I had a problem.


It turns out that the CB don't protect the 2N2147s. Two of the four on Ch B now have a dead short from collector to emitter.


I have several choices:


1) Give up - chalk up the losses - 'A Good Choice.'


2) It seems like there are no new 2N2147 actual replacements available at any believable prices. Perhaps, it might be possible to buy some old, expensive ones. They could 'go bad', too. This is 'A Sketchy Choice.'


3) Replace the 2N2147s with modern, current production, Silicon TO-3 output transistors. Revise the bias network to make that work. For example, ON Semiconductor MJ21193G TO-3 PNP are $6.71 each on DigiKey. They should do the job, and only two per Ch are actually needed since the MJ21193G seem to be a lot more powerful. This is a 'Decent Choice.'


4) Convert the output stage to 'Full Complementary' with a revised bias network and some re-wiring. ON Semiconductor offers the MJ21194G TO-3 NPN for this purpose - those are $7.06 each on DigiKey. This is another 'Good Choice' with some upside potential.


Since 3 and 4 will will require another total disassemble, this is a tough decision.


I will appreciate all responses.