RCA 3028a opamp?

[soundguy]

Anyone have any experience with an old RCA opamp CA 3028a? Its in a round can, looks like a big transistor. I found this spec sheet which has a schematic of the circuit-

http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=511380

two questions-

1. Can anyone reccomend a replacement, form factor is not important.

2. Is there anyway, looking at that datasheet, to plug in some parts to just build it discrete? Thats definitley over my head, figuring that out...

thanks

dave

 

[bcarso]

It's not an op amp, despite their circuit symbol, just a simple differential pair (Q1, Q2) with a current source supplying the emitter current. A discrete rendition would be easy---they have given you the complete schematic in the datasheet.

About the only advantage of the IC besides the size is the matching and proximity of the two transistors in the differential pair. Otherwise some garden-variety NPN's like 2N3904s could be substituted.

Is the part already in a system and you want to replace it or substitute something for it? The application will determine how important the transistor matching might be.

 

[Family Hoof]

Dude, that'd be totally easy to build. 3 resistors and 3 semis. Piece of cake. Like Brad says, the application should hint as to BJT performance requirements and how closely matched.

What's the context?

 

[soundguy]

thanks for the info guys. The part is on a line amp card I have sitting here, was thinking of making some changes, just wondering what that thing was.

dave

 

[adrianh]

Mr. Dave

National makes a diff pair that is matched to a nat's hair.
http://www.national.com/ds.cgi/LM/LM194.pdf

Just place a transistor current source at the emitter and away you go.
The part is very expensive.

also Thatcorp.com has matched transistors too.

Or just use 2N3904 and match them.