Craigmoates

Good point, thank you! I'll segment things by amp moving forward if that makes best sense. Here is the post for the unit shown:

Thank you for the welcoming words. Looks like i'm expanding the collection to also include additional units: 1x M240, 2x M4060, M4120, M2120, and M2020. Plenty of refurbish, improvements, and probably some diagnostics/repair on the horizon. I've taken the PMA2150 apart for inspection and recap. Comparing it to the M240/M2120 schematics and layouts, it's similar in some ways but a different animal/design, without the more interesting multi-rail commutation and such. Single sided board, it uses TL494N instead of 3524 for switching. Stranded vs solid core coil. Different op amps (JRC2060/4558D/AN6551, not 4136). Looks like MOSFET (YTPF150) on the PS vs older design (MJE2340/50 sub TIP35/36B, both PS and out), with couple of 2SD817/1047 pairs on the output for the later PMA. The PMA2022 looks ultra basic, didn't even open it yet. Just an integrated TA8220H surrounded by passives and terminals. I'd say not much thought was needed for this particular design. Anyways, interesting enough to get me started! I'll be sure to provide plenty of content in terms of photos and details.

Hello folks, I'm chiming in here to say hello. Had an M240 back in the 80s, purchased new. Pushed a few CVs with it, namely a single 18. Ran passive xovers, always wanted to afford biamp/second unit. This amp had brilliant range, very dynamic. Right when portable CDs were becoming a thing. Being a teenager, we burned it up (rectifier/diodes, fets). Bought the service manual and learned a thing or two, repaired and back to goodness for years more. Eventually stolen. Poking at that old amp inspired me in several ways. From hands-on learning about switching supplies and general electronics design/repair to appreciating what it means to put your name behind a product you create, it was a pivotal experience. Now, 40 years later, picked up a pretty much NOS M240 (Ser#2600, early unit, pulled from a Model-T from what I was told!). Then a truly NOS PMA2150 and PMA2022 (from the factory shutdown in the 90s). The back story is half the fun with these. On the hunt for an M4120. Coming through here to learn and share, yall seem like a good crew! Thanks for the welcoming vibe, Craig Moates