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Help with transistor equivalent

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texaslonghorn

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am looking for current replacements for 2SD555 and 2SB600 complementary pairs. I am getting confused by the xref info I have found. Any specific info/suggestions greatly appreciated. Thanks.
 

k7elp60

Active Member

mneary

New Member
Replacement xref guides are only guides. There's no real substitute for knowing the transistor requirements.

Are you repairing something, designing, or building?
 

texaslonghorn

New Member
Hi. I am updating a 1970s Phase Linear amplifier. The original output transistors are obsolete, but some are available on ebay. However, research indicates there were quality issues with them, so I would like to upgrade to a suitable current transistor. Hope that helps.
 

mneary

New Member
Was there a quality issue with the transistors themselves or with the amplifier design? The 2SD555 and 2SB600 look like an ordinary (but old) high power complementary pair. As noted on many web sites the MJ15022-MJ15025 family look like they exceed the specifications. Other suggestions are made for using MJ21193-MJ21196 which also look good.

Are you confused that many different transistors look suitable? It's not uncommon, because for the most part you're just trying to exceed the ratings of the original 1970's transistors. Check voltage and current rating, gain, and bandwidth.

Plenty of voltage and current rating is good. For gain and bandwidth, you shouldn't have too much or too little. Second breakdown performance is new since the 1970's, and could be why the old devices had a bad rep.
 

texaslonghorn

New Member
You hit the nail on the head. Yes I am confused. There is such a thing as too much information and too many choices. But after more research, I think I settled on the MJ21193-MJ21196 pair you mentioned. I had a great experience with MJ21193/94 pairs recently on another project and am quite pleased. Thanks.
 
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