Thank you all!! That was exactly it, the LM-1877!
Actually, now that you mention it, I recall seeing it in my Forest Mimms books from Radio Shack years ago. And Mike, thanks for confirming the details of the circuit operation for me. Thanks again! Albert BTW, I thought I posted a reply earlier this evening but I haven't seen it yet. If two messages pop up from me it is because Yahoo is retarded. --- In Repeater-Builder@yahoogroups.com, Mike Morris <wa6...@...> wrote: > > At 01:19 PM 07/23/10, you wrote: > >Hey Guys. I was looking at the schematic for the above mentioned > >speaker (thank you repeater builder site) and I had a few questions. > > If anybody's interested it's here: > <http://www.repeater-builder.com/motorola/genesis/pdfs/nsn6054a-68p81108c39-o.pdf> > > >First, does anyone know where to find a replacement for the > >5184320A99 dual op-amp labeled U1? > > I'd look in the National Semiconductor products manual > that covers automotive audio products. > That schematic resembles what I saw in an early 1980s app > note for a car stereo receiver. LM187something. > > >Secondly, Is this op-amp basically being used as a buffer, preamp, > >and inverter? > > Both halves are being used strictly as an inverting buffer > for out-of-phase audio. > > Look carefully at the schematic and remember that > nothing in the input circuit is ground referenced - the > audio input (from the radio) is balanced audio (both > are sides hot, 180 degrees out of phase with each other, > and there's an implied / virtual audio ground) in the > middle. > > Each side of the circuitry driving the speaker is a mirror > image of the other, just like the incoming audio is a > mirror image compared to the virtual ground. > > >Thirdly, what on earth are pins 3, 4, 5 and pins 10, 11, 12 doing? > >I have never seen so many pins on an op-amp tied together. > > If that chip is the one I'm thinking of its capable of about 2 watts > per channel on it's own. That takes some heat sinking. > Probably a heat sink for the final transistors inside the opamp. > And if you look closely, pin 1 is audio ground, and pins 3,4,5, > 10, 11 and 12 are power ground - and those are switched to > ground by Q3, which is driven by the squelch circuit in the radio. > > >Thanks! > >Albert > > Mike WA6ILQ >
