Mcintosh MC2200 recap

[Sakharov]

To all amplifier gurus,

I'm a proud owner of a 37 year old MC2200. It's working perfectly, but the age is there. To further enjoy a few more problem free years I believe it is time to do an overall. My main idea would be to replace the electrolytic capacitors (except the big filter caps). Will it require bias adjustment afterwards? Would it be possible to do it with only a multi-meter?

I'm a newbie in electronics with some basic equipment and good soldering skills.

thank for all your suggestions

 

[indianajo]

I find I can repair amps in a non-production environment with only a DVM a VOM, a portable FM radio with earphone jack, an 8 ohm load, some wires and adapters, and a speaker. The DVM is for checking DC voltages and resistances. The VOM with 2 vac and 20 vac scales is for tracing AC music through the circuit in case you caused a problem with a bad solder joint. The radio is for making the music you can trace, and rock stations produce a heavy beat in the VOM pointer which doesn't look like ultrasonic oscillation, which is high and steady. Oscillation can be caused if your soldering interrupts the path from drivers to output transistors. You need a .047 400v cap to block DC when making AC readings on the VOM Ac scale. A blocking 390 pf cap would pass ultrasonic oscillation, but not music.
The 8 ohm resistive load checks your rail capacitors before and after cap replacement. If the amp is putting out the rated power according to (V^2)/R=P, then the rail caps aren't low capacitance or high ESR yet. Use the VOM for this check, most DVM produce random numbers on music frequencies.
I don't see the MC2200 schematic , but see this thread, I think the sender is still posting. http://www.diyaudio.com/forums/solid-state/164210-mcintosh-mc2200-schematic-sm-wanted.html
I fixed my first transistor amp without a schematic diagram, but due to guessing at a number of burned parts, I limited the power out to 15w on a 60 w/ch amp. PTL we have the internet now.
I try to buy capacitors rated at higher than 3000 hour service life. Smaller ones can be had in 10000 at 105 deg C grade. See digikey or farnell, other suppliers make you download the datasheet to sort out the 1 year life 500 hour caps. Mostly, they sell the 500 hour ones, the long life ones are a bit rare. I haven't sorted for ESR or "audio grade" but in this premium category I haven't had a problem yet. I've replaced several hundred caps in amps and organs, as well as repairing one amp that needed 114 parts. No scope, no spectrum analyzer, no gain matching tools. If changing output transistors, ask about matching Vce in sets, with a DVM check a couple of resistors and a 12 v power supply.
Don't forget to inspect for any mica washers under power transistors, they start looking bad about 40-50 years. Use heat sink grease, which is poisonous, wash your hands. Wear safety glasses for checks, if you blow a transistor top off it might save your eyes. Follow one hand at a time rules with the power on, to keep current from flowing across your heart and stopping it. Use alligator clips for the meter negative. No jewelry on hands or neck, no distractions with the power on.
I find if you don't change transistors OT idle currents don't go off, but you should check them anyway. See the manual, but 20-40 ma through emitter resistors is usual for TO3 package OT's. See this thread about idle current in general http://www.diyaudio.com/forums/solid-state/136261-vintage-amplifier-repair-upgrade-manual.html
commercial guys like him are obsessed with idle current and output transistors, OT's get blown a lot in bar amp due to the dodgy wiring, and sometimes cheapo amp design. Not usually a problem with Mac's.
Clean your heat sinks.
Best of luck.