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Pioneer SX-1250 full restoration. Output transistors to replace or not to replace

Kingbleu

Kingbleu

Well-Known Member
What are your thoughts about replacing the 8 output transistors on a Pioneer SX-1250
Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8

Original part numbers:
Q1, Q2, Q5, Q6, 2SB600-R
Q3, Q4, Q7, Q8, 2SD555-R

Replace with
Q1, Q2, Q5, Q6, 863-MJ21193G
Q3, Q4, Q7, Q8, 863-MJ21194G

I am getting ready for a fulI bones, bar none restoration. This unit is unmolested and all the functions work. However there is a issue with one of the channels being weaker than the other. Weaker in decibels, timbre, and bass. This is something that becomes apparent when I switch the balance left to right. I already replaced the big Filter caps with some blue Adcoms but that didn't help the problem.

Any how there is a complete recap list here on AK that was made by mattsd, thank you mattsd. I ordered all the parts on the recap list on April 16, and have received most of the parts but there are a handful of caps that are on back order and they wont be here until the end of June.

I noticed the 8 big metal output transistors Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 are missing from this recap list. Is this one of those things that you don't replace unless its broken? Or should I add them to my order? Thanks
 
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Just because they are "working" doesn't mean that they are in good condition. You need to test them for hfe and leakage. A cheap transistor tester will work fine. I have an Heathkit it-1320 and a atlas dc75. I am currently working on a Marantz 2265B. When I got to the amp section, I pulled the output transistors and although they didn't leak they measured; pnp 56 & 56 good (they match too) and npn 52 (good) & 31 (ugh). Looking at the datasheet, 40 hfe is minimum, out they go and they were replaced. Not the first time and it seems there's is always one, usually an npn, that needs replacement. The lowest hfe on a working amp I've found is 11on a Sansui Au-9900. So yes, they work, but as you start using this receiver and showing others how loud it is, if an output transistor is out of spec, it may blow (short) or just fail (and you'll blame your recap).
I'm saving all my in spec output transistors, hope to one day have a working set (but since even among the same manufacture and same year, they seem to use different output transistors).
 
Save the old ones, and go with new - your future self would thank you - IF they popped.
BUT since you went with new ones (cheap insurance) that time loop NEVER happens!!

The future availability of TO-3 type power transistors is not guaranteed, indeed, it becomes less likely as time moves on, and trying to adapt TO-247 cases to the heat sinks will be a PITA.
 
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