McIntosh MA 6100 Integrated Amp
We recently got this McIntosh MA 6100 integrated amplifier in for a restoration. This is a 70 watts unit built from 1972 to 1979. This unit was functional, but original. It also had a severely cracked glass faceplate, which the owner had purchased a new one to replace it.
This unit had quite a few axial capacitors and a few bipolar caps as well. They needed to be ordered, along with the large filter caps, and the multi-section cap had to be sourced that would fit. We also needed to get new lights for the unit, which will be swapped to LEDS. The parts were all recorded and ordered.
This unit, for the most part, is incredibly easy to work on. The circuit-boards are all cards that plug in, and come right out of the unit. Parts count was also quite low. That means… a short signal path! The large, main filter capacitors fit in perfectly, and the multi-section cap went in pretty easy as well.
On the left, the before and after preamp boards, and the right, the amp driver boards. All pull out completely from the unit for easy access. On the preamp, the orange caps get new low-noise Nichicon KL caps. The old gray caps are filtering, and change to Nichicon high-temp/high-reliability PW caps. On the amp, the orange caps are bipolars which are replaced with Nichicon MUSE audio grade caps. The tantalum cap goes to a low-noise Nichicon KL cap. The vertical axial filtering cap changes to a radial PW. The other axial we needed to order, goes to an axial Vishay electrolytic.
The regulator/phase inverter board is simple. The gray radial cap gets changed to a Nichicon PW, and the two axial caps are replaced with Nichicon VX electrolytic capacitors.
The axial electrolytic underneath the regulator/phase inverter board gets changed next with another Nichicon VX axial cap.
Be careful of the (what looks to be) Schottky diode and also make sure you make the solder joints clean enough so you’re only connecting to the right pins.
While the boards were all out, we took a microfiber cloth to clean up all the grungy dust from the chassis.
This unit was in great condition, other than the broken faceplate. The chrome chassis still looks new!
We were able to find the perfect swap for the old main filter caps. Mallory 10,000μf/75v go in, and the 9,300μf/50v come out. As you can see they are the same size, and the terminations are the same type and size. Unlike the modification we had to do on that McIntosh 4100, with the 3-D printed collars, these drop right in!
The original multisection cap is: 80μf @ 200v/150μf @150v/150μf @150v/200μf @100v. The last section was unused.
The new one, ordered from Hayseed, closest cap we could find to a drop in replacement… needed some help to work. The new cap is: 80μf @250v/80μf @250v/150μf @160v/50μf @160v.
We need to add a 68μf capacitor to ground, in parallel with the first 80μf section of the new capacitor. The rest of the capacitor connects back as the old one came out, the last section of the new cap also being unused. The new cap is wider, by maybe 1mm, so it will not fit through the chassis. rather than cutting the chassis to make a wider hole, we flipped the spacers on the original metal wafer, so now the wafer was mounted right to the chassis. The old cap was much shorter, so it worked perfectly! It even sits flush with the filter caps, as the old one did.
Too worried about messing up the new glass faceplate… I didn’t take very many pictures of the faceplate swap and the LED installation. Here’s what I snagged.
The old faceplate was removed, and taken out of the front frame. The old foam behind the faceplate was removed and replaced. The old diffuser was removed and aligned to the new glass. It is then installed into the front frame again. The old bezel was carefully removed and attached back onto the new glass faceplate… being very careful with lining it up straight!! The old lamps were replaced with LEDs while the faceplate was off. That’s about it… patience, steady hands, and carefulness is key to doing this right. Imagine breaking the new glass? Exactly.
That’s about it! We put it all back together, checked some measurements, back into the wood case, and it was playing and looking great! This was a nice unit to work on. The worst part is the faceplate swap. It makes me nervous.