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Old 12th August 2007, 08:40 AM   #1
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Default adcom 555II part sources

Hello,
Im rebuilding the output stages on my 555II. This is my first refurb on an amp this size. I viewed many threads on diy and found tons of usefull information (thanks everyone). My question is in regards to the sources of parts. specifically transistors. My biggest concern is mathcing the o/ps. (mj15025/15024s ON semi) Is this absolutely nessesary??? Ive been told both yes and no as long as the transistors are from the same production batch. Can any one recommend a source for 2sd1047/2sb817 2sc2912/2sc2240 2sa1210 or subs for these transistors.
Thanks for your help
Steve
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Old 12th August 2007, 01:10 PM   #2
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Matching is nice, but if the transistors are from the same run they'll be fairly close. Plus, the 555II has 0.22 ohm emitter resistors to help with current sharing if gains are off a bit (if the amp blew up, you must check these emitter resistors).

The On-Semi MJ21193G and MJ21194G use a perforated emitter technology similar to the original 2SD424 and 2SB554 transistors, and IMO would be a better match.

On-Semi MJE15032 and MJE15033 will make fine TO-220 drivers, and Sanyo makes the TO-126 2SA1380/2SC3503 predrivers that will do a good job replacing the original 2SA1210/2SC2912 combo (which I think were also Sanyo devices).
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Old 13th August 2007, 07:09 AM   #3
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Thanks for your reply Echo Wars
My biggest concern with the matching o/ps is I would rather not have to buy 30 pairs to get 5 matched up. I see AmpsLab sells matched outputs but for quite a premium +$10 each. Ive also found direct sanyo replacements for the drivers and predrivers from MCM. Have you or anyone else had any experience with this company. Another concern of mine is fakes but thats whole other topic.
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Old 13th August 2007, 08:26 AM   #4
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I buy everything I can from Digikey, Mouser, Newark, and B&D Enterprises. I don't trust anybody else...been burned too many times from companies that don't care (MCM being one of them).
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