Replacing multi-caps.
Referring to the power supply schematic in the MC250 SM, capacitors C29A, B, C and D provide filtering for the 93 and 82VDC rails. These are sections of a multi-cap that's located on the top of the amplifier chassis.
Rather than removing and restuffing the cap can with individual electrolytics, I have found it significantly easier to add a solder terminal strip as shown below and rewire directly to the strip. The supplier of the terminal strip is Abbatron. The terminal strip is mounted on aluminum standoffs that are screwed to existing standoffs on the amplifier power supply board.
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Replacing the mains filtering caps.
There are no equivalent replacements that are the same height. Terminal spacing a can diameter is same as original. As is shown below, if you use a wooden case, you have a fit issue(!). Note PN of replacement cap in photo, supplier Mouser.
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Replacing the preamplifier board.
The customer requested replacing the stock preamplifier board with the North Reading Engineering replacement. The OEM unit is shown, last photo.
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Replacing output transistors.
OEM transistors replaced with MJ15003G ONSEMI. Be wary of counterfeits, purchase from factory distributors (Mouser for example).
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Replacing C57 filter capacitor.
For the -40VDC rail (filtered), there's a direct replacement (Mouser 539-CG501U150R3C) but requires the use of a cap clamp (Mouser 539-VR3). The OEM cap is riveted to the chassis, drill the bottom side of the rivet to remove, use a 1/4 or larger drill, slow speed.
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Nice work as usual! Thanks for the info of those terminal strips. I have bookmarked Abbatron, those are pretty slick. This is the kind of detailed info I was hoping for when joining your group. Thanks!
Jeremy