Upgrading a Dynaco PAS tube preamplifier.
Mcintosh mc 250 schematic update#
Mcintosh mc 250 schematic manual#
Next time I'll bypass the main reservoir capacitors and replace the other aging electrolytics mounted on the PCB boards.įor schematics and part values the McIntosh MC-250 service manual is available here. Of course old electrolytics should be replaced anyways as a safety measure. Some people may prefer the vintage sound - so keep this in mind if you are thinking of upgrading any old amplifier. There appears to be more detail too - but I'm doing comparisons by memory so you can take this observation with a grain of salt. The original capacitors are over 30 years old and must have drifted in value since then. So how does it sound after the changes? It definitely makes the MC-250 sound 'less vintage' with a more modern representation. 47uF capacitors were tight fit and needed to be raised off the board a bit in order not to interfere with nearby components. Here you can see the new capacitors are mounted. It certainly would help to have a 3rd hand - one hand to hold the board still, the other hand to pull on the leads of the old component and another to handle the solder iron. Also be sure not to bend the attached wires too much as these can also break. If you do this yourself, be sure to work carefully since these vintage PCB boards are fragile. I applied my soldering iron and removed the old parts. Once the two bolts on top have been removed you can see the bottom of the PCB board. The input capacitors are replaced with Ero Metallized Polypropolenes and the output capacitors should be replaced with bipolar electrolytics. Here are the parts (circled in red) that I am going to be updating: the main input board power power supply capacitors will be increased with 1000uF Philips units. I wondered if anyone has a recommendation for a preamp. I think I can run it through the preamp section of one of these for now. I have two scotts, a 233 and 222, and a H/K 730. I decided to give my McIntosh MC-250 a much needed update - here is the input board: I just bought a MC 250 from fellow forum member Kevin in Chicago.
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