Help finding a replacement for obsolete transistors

Thread Starter

John Czerwinski

Joined Jun 19, 2017
44
I'm working on an old monitor. The following obsolete transistors have failed and am trying to find replacements:
2SC1685 - 100mA, 50V, NPN, Si, SMALL SIGNAL TRANSISTOR, TO-92
2SD478 - TRANSISTOR,BJT,NPN,150V V(BR)CEO,2A I(C),TO-220

I've attached the datasheets for both devices but need some assistance to know which attributes I absolutely need to match 100%, and which ones may be ok to go higher/lower. Since there both used to amplify, I'm pretty sure HFE has to match as well as the Ic amp and voltage ratings
 

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MrChips

Joined Oct 2, 2009
23,055
My take is that you don't have to match anything 100% exactly except:
  1. semiconductor type, Ge vs Si
  2. polarity, PNP vs NPN
  3. package
  4. lead identification

Check that the following match or exceeds original:
  1. voltage
  2. current
  3. power dissipation
  4. gain
  5. frequency
 

abrsvc

Joined Jun 16, 2018
62
According to my cross reference guide:

2SC1685 crosses to: 2SC1815, 2SC945, 2SC1740 among others (these are very common)
2SD478 crosses to: 2SC2073, 2SD401A, 2SD1138, 2SC901, 2SD1562A

Dan
 
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