MC30 pair for restoration

[nre_admin]

Deep pitting and blister on both the top chassis cover chrome plating and bottom cover paint, heavy scale (corrosion) on the bottom covers too.  There's a supplier in Singapore that makes a top cover replacement and the gent that owns these purchased a pair and provided them to me for this rework.  The bottom covers are steel sheet and can be grit-blasted, chem-etched, primed, sprayed and then baked to a like new condition.  The cast McIntosh emblem is a pot metal casting with a copper strike then chrome plated.  These usually pit but bench out nicely on a stationary belt grinder and can be left in a benched condition.   

Both power cords showed signs of rodent damage.  Likely been sitting for some time out of sight.  The internal components are original, nothing's been replaced.

The workflow used on these:

1. remove power cord, Heyco strain relief, fuse holder

2. remove bottom cover, work separately.

3. remove transformers, check for troubles.

4. mask tube and octal sockets.

5. grind out rivet tops, all rivets.

6. remove as much of the internal circuitry as possible without breaking connections this includes the board and the sockets and pots attached to it.

7. remove barrier terminal, soak in cleaner, replace #6 fasteners with combination type

8. On the board replace germanium rectifier and dropping resistor with silicon, replace Bumblebee and Black Beauty caps with polypropylene types.  The Bumblebee caps have high leakage current at rated voltage, must be replaced.

9. Replace single can electrolytic caps for bias supply, preamp

10. On replacement chassis top install new RCA input, barrier terminal and octal sockets, new fuse holder, new multi-section capacitor for power supply (CE Mfg).

11. Reinstall reworked board, pots and tube sockets

12. Install transformers

13. on Variac, spool amp up and measure all voltage magnitudes

[nre_admin]

Sheet metal bottom chassis parts grit blasted, chemically etched, primed, painted then baked.

[nre_admin]

New, reproduction chassis tops from Korea.  Not sure if they're fabricated in Korea.  Quality is better than the original.

[nre_admin]

Removing the circuit as a whole assembly simplifies the rebuild process.

[nre_admin]

Recapped, replaced power cord, fuse holder, u/s clean of terminal barrier block.

[nre_admin]

Replace multi-section cap with CE Mfg 80-40-30-20 550VDC.  The 30MF isn't used.

[nre_admin]

Completed pair.