MC225 restoration

[nre]

MC225 for restoration and new top cover!

[nre]

First thing is to dismantle it down to its bits and pieces.  The brown capacitors are Mylar and age well.  They do not need to be replaced but should one desire, replace with polypropylene.

The multisection cap, the Bumbleebee caps and the Al-elctrolytics must be replaced.

[nre]

The rectifier/bias supply board is reworked.  Here I used 1N5408 rectifiers (Diotec Semi) and replace the brown Mylar with a WIMA MKP of equivalent value (0.47uF, 250VDC).  A 0.01uF, 2-3kV Gap-Kap across the rectifiers to suppress diode noise.  As received, the bias supply had a 1N4007 diode installed which tested good and was left in place.  The 100uF Al-electrolytic is for bias supply filtering.  A RAD Nichicon was used here.

[nre]

Installed the power supply transformer and one of the output transformers onto the new top chassis. 

[nre]

Power supplies and wire looming complete.

[nre]

Completed amplifier and %THD at 1kHz.