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Motorola Transistor Equivalents? MPS1761/SPS1761

T

the groke

New Member
Hi,

Would anyone be able to provide me with the specs and a possible substitute/equivalent for an old, 70s Motorola NPN transistor - MPS1761 aka SPS1761. It is in a TO-202 case.

I checked Towers (and Google of course), but I can't find any info on this particular transformer. I know some members have old transistor equivalent books... I'm hoping one of the 1970s Motorola books might list it.

This is the circuit it is in (Q3):

http://www-personal.umich.edu/~damont/MartiCA-40.pdf

Thanks - DT
 
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Hi. That's a good point. I doubt they will have the datasheet specs, but they might have a cross-listed replacement part. I know they still have info on at least some of their old part numbers on file...

But if anyone has access to an old Motorola cross-listing, please still let me know.

Thanks - DT
 
That must have been a house number or in production for a week and a half. Or maybe another company decided to use the MPS series to number it. None of my early Motorola books list it, nor do any of my cross references. MPS was invariably small signal, not power. I'd determine if it was Ge or Si (DMM on diode check across a good one), then use something more common, maybe in a TO-220 case. The TIP series might work, maybe TIP-30 or TIP-32?
 
Hi ConradH,

Thank you so much for checking. It definitely has a Motorola symbol on it, and it uses a very unusual (to me) TO-220 style case (I think the case style is actually called 152-02). The same case as is seen here:http://www.abra-electronics.com/products/MPSU01-Transistor-Audio-NPN-2A-30V.html

But I don't really understand the function in the circuit (I'm a bit of a hack). It's feeding the lamp end (not LED) of an optocoupler. I thought it was part of a detector circuit? Any thoughts on this? The schematic is in the link in my first post.

Thanks - DT
 
There were various devices with small non-standard tabs for a bit higher power dissipation. I don't know much about the circuit as there aren't any resistor values and I don't know what it does (effect pedal?). Because it's driven by another device the way it is, almost anything should work. It just needs to have a higher voltage rating than the supply and be capable of the power of the original device. The TIP is certainly a higher power device and I assume the voltage is quite low. Man, I hope nobody is actually paying $9 for obsolete low power audio transistors!
 
Hi Conrad,

Thanks for the info. It's a compression module. The schematic is followed by a list of resistor values (scroll down to the next page). But, I think you made your point. I will try the NPN version of the TIP you suggested.

Regarding old transistors. The whole process of substitution is a mystery to me. I've encountered some stuff where 3904/3906 can replace the old, obsolete part without issue or adjustment, but I never really know if and when I need to be more exact. and I know I'm not alone in my confusion (amongst newbies at least). Perhaps I should start another thread asking people to contribute tips for determining whether an exact substitute or a general substitute is needed...

best DT
 
Hi.. Just thought I'd poke this old thread.

I have the same transistor (MPS 1761), in the same Marti CA40 compression module that seems to be dead. Base voltage varies, but the collector (which drives the Vactrol) just sits there. It's not drawn as a Darlington on the schematic.

Just wondering if The Groke found a suitable substitute? It does not show up in the NTE cross reference BTW. I've never understood manufacturers using custom numbered transistors...especially to drive a light bulb.

Thanks,
Dave O.
 
Update MPS 1761 transistor

Just in case someone else gets into one of these compressors...

I did some experimenting with different NPN transistors today. The one that seems to most closely match the performance of the original Motorola MPS 1761 is the NTE128. Still (thankfully) quite available.

This Marti compressor/limiter has been playing happily for several hours now with no problems.

Dave O.
 
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