I'm not suggesting that this post become a sticky, but if the our resident experts share valuable information perhaps so. I'm in the middle of searching for replacement transistors for a Pioneer Amp - power transistors to be precise, but it could very well be any transistor in the amp at this point as they are all "obsolete"
Picking other components (caps, resistors, diodes, etc.) seems pretty straight forward, but transistors have quite a few parameters.
I see lots of posts from people asking "I have this [insert nomenclature] but I can't find originals any more, what do I replace it with?" No surprise, I am in the same boat - especially being a novice.
I've read a couple of articles on the interwebs that give the basics like,
Make sure Vceo/Vcbo is = or > than original
Make sure hFE is in the same range (O/Y/P or other designater)
Make sure Ft is equivalent,
and
Make sure Ic Max is = or >
oh, and form factor!
Sounds reasonable to me, but here is the question...
When is close, close enough, and when is close not close enough?
For example:
I started looking for 2SA1104-Y and it's compliment. They are obsolete - hens teeth now.
I found to be what seems a direct replacement: 2SA1694Y/2SC4467Y. They do not appear to be obsolete, but they are basically not in stock anywhere that I can tell or in any great quantity (perhaps covid related shortage?)
Other candidates in the same form factor are 2SA1909 and 2SA1695 (and complimentary)
When do the values of Vceo/Vcbo or Ic Max or some of the other parameters become too far away from the original?
And, what are some of the best sites that allow for searching on these parameters?
Picking other components (caps, resistors, diodes, etc.) seems pretty straight forward, but transistors have quite a few parameters.
I see lots of posts from people asking "I have this [insert nomenclature] but I can't find originals any more, what do I replace it with?" No surprise, I am in the same boat - especially being a novice.
I've read a couple of articles on the interwebs that give the basics like,
Make sure Vceo/Vcbo is = or > than original
Make sure hFE is in the same range (O/Y/P or other designater)
Make sure Ft is equivalent,
and
Make sure Ic Max is = or >
oh, and form factor!
Sounds reasonable to me, but here is the question...
When is close, close enough, and when is close not close enough?
For example:
I started looking for 2SA1104-Y and it's compliment. They are obsolete - hens teeth now.
I found to be what seems a direct replacement: 2SA1694Y/2SC4467Y. They do not appear to be obsolete, but they are basically not in stock anywhere that I can tell or in any great quantity (perhaps covid related shortage?)
Other candidates in the same form factor are 2SA1909 and 2SA1695 (and complimentary)
When do the values of Vceo/Vcbo or Ic Max or some of the other parameters become too far away from the original?
And, what are some of the best sites that allow for searching on these parameters?
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I use datasheetcatalog.com to look up parameters of each industry type. 2SA & 2SC are pretty well documented, also bc-, bd- and 2n-
Vceo can be misleading when they do things like test at 100 ma leakage. Much higher Vceo than rated can come at a cost of much higher cbo, which takes more current to drive at higher frequencies. Like I don't use 300 v rated parts if a 120 v rating will do. I do use 80 vceo rated parts for 25 v originals. Successfully.
Excess hfe can be bled off with a collector to base resistor if the higher gain gets to be a problem. Most modern transistors (from ON, anyway) are much higher gain than available in the 60's & 70's. Much quieter too, no dust or skin flakes floating around the fab facility these days.
Ic max tests the bond wire. soa current @ the voltage used in circuit is much more useful, but mostly not available except from ON and toshiba.
Ft is mostly not specified on replacement parts, NTE central semi NJ semi etc. Even fairchild leaves out Ft on parts like bd139/140 . Original seimens/phillips/telefunken bd139/140s with ft specified are not available to me.
I'm not looking up those obsolete parts you're looking for, but if TO220 case, I usually use MJE15028/29 for lower voltages (lower cbe) or higher voltage MJE15031/32 if necessary. In TO126 fairchild KSA1220 and KSC2690 are sometimes in stock.
Vceo can be misleading when they do things like test at 100 ma leakage. Much higher Vceo than rated can come at a cost of much higher cbo, which takes more current to drive at higher frequencies. Like I don't use 300 v rated parts if a 120 v rating will do. I do use 80 vceo rated parts for 25 v originals. Successfully.
Excess hfe can be bled off with a collector to base resistor if the higher gain gets to be a problem. Most modern transistors (from ON, anyway) are much higher gain than available in the 60's & 70's. Much quieter too, no dust or skin flakes floating around the fab facility these days.
Ic max tests the bond wire. soa current @ the voltage used in circuit is much more useful, but mostly not available except from ON and toshiba.
Ft is mostly not specified on replacement parts, NTE central semi NJ semi etc. Even fairchild leaves out Ft on parts like bd139/140 . Original seimens/phillips/telefunken bd139/140s with ft specified are not available to me.
I'm not looking up those obsolete parts you're looking for, but if TO220 case, I usually use MJE15028/29 for lower voltages (lower cbe) or higher voltage MJE15031/32 if necessary. In TO126 fairchild KSA1220 and KSC2690 are sometimes in stock.
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2SA1805 --"O" or "R" is quite near it .
Of course there are later versions but I am not looking through a whole large equivalents book but its available . I will let somebody else look for others --the "Y" is only a higher Hfe range than the basic one .
Of course there are later versions but I am not looking through a whole large equivalents book but its available . I will let somebody else look for others --the "Y" is only a higher Hfe range than the basic one .
Are any of these equivalents books available on the internet. Perhaps maybe a searchable index?
For this thread, I'm not specifically looking the for replacements of the example above, What I'm trying to do is "pick your brains" for the process or rational for choosing replacements for obsolete transistors. Like which parameters count the most and why.
How its packaged- lead info-maximum voltage -maximum current-gain factor (Hfe ) - its use in audio -type- BJT/Fet/Mosfet /IGmosfet / etc --is it low noise - is it for SMPS- speed in switching this just goes on and on .
Its already out there if you look --free ?-
ECG Semiconductors Master Replacement Guide (1989) : Free Download, Borrow, and Streaming : Internet Archive
Its already out there if you look --free ?-
ECG Semiconductors Master Replacement Guide (1989) : Free Download, Borrow, and Streaming : Internet Archive