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Mitsubishi M-A04? Anyone Know Anything?

AlexHempel

AlexHempel

AK Subscriber
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So I got kicked out of the dorms (coronavirus) and decided to restore an amp to help pass the time back at home. Also to drive my Stax headphones (had to leave my beloved Pioneer M-22 behind in NYC).

I was browsing eBay and stumbled across this thing: https://www.ebay.com/itm/Rare-Vinta...321910?hash=item48deb928f6:g:680AAOSw0j5eMcXO

There's not much on the internet, but I love the form factor, and I'm a sucker for external heatsinks. Was wondering if anyone has ever heard or worked on one. Manual indicates it has four ICs, which is giving me pause -- I'm assuming they're unobtainium.
 
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G'day..
If you're referring to STK's .. the unit doesn't have them. Pdf page 8 in SM bottom right corner shows relevant transistors.
However I'd be cautious buying off the bay.. assure unit is working or not and get seller to reveal as much info as possible. You can always send an offer considering any faults. and assure gorilla proof packing /shipping.
----------Pdf page 8 in SM bottom right corner shows relevant transistors.
Service manual for gentle readers:
https://www.hifiengine.com/manual_library/mitsubishi/m-a04.shtml
 
@Binkman I'm referring to these ICs:

Mao4ICs.png
ICs.png

I know they're not STKs, but I try to avoid all ICs when possible. And I do assume everything I buy off eBay is broken, even when the seller claims it's working.
 
@Binkman thanks for those suggestions. I was also worried about Q101 and Q201, which are 2SK109 dual JFETs, but it appears the DIYaudio store has matched discrete JFETs that can be used to fashion a replacement.
 
Binkman said:
Yes your concern is valid these 2sk109's are potential issue and likely will fail or can be erratic and maybe circuit dependent. I just don't have the experience to make a rock solid answer. soo.. Paging: @avionic @dlucy perhaps can chime in.
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did dig up a couple threads.
https://www.diyaudio.com/forums/parts/172347-2sc2631-2sc1953-2sk109-equivalents-2.html
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=5073
Click to expand...

thanks for the nod, but I have to draw the line of what I know at JFETs and let someone who actually understands them respond.
 
AlexHempel said:
DIYaudio store has matched discrete JFETs that can be used to fashion a replacement.
Click to expand...
Arrange to go back and get your amp!
Right there; these ic's may be the deal killer and costly.. some direct replacement originals upwards of $45 ea. much cheaper in bulk where available. There are alternatives however these act in some cases on NFB and or auto biasing circuits You can get ic's and the adaptor pcb's, I've read on a.k. used on two Sansui models. You can get away using a DMM but a Scope would be much better. I have not studied the SM so you would have to determine if these are a common complimentary amplifier application or used in a self biasing circuit.
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Pretty obvious reason the selling is selling it. But no way pay the asking price plus shipping.
 
@Binkman thanks for the advice. I think I'm gonna go with a Sony VFET amplifier instead. That also has unobtainium but the seller assures me it's working and offers returns. Cheers!
 
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