Please excuse the poor image quality of the pictures on this page, they were taken with a household-grade camcorder, and an ATI video capture board, instead of a real digital camera!
September 23, 2001:
This is the latest restoration project I am getting into. I am not only doing this to help out a good friend, but to perserve a piece of electronic and technology history. There are two amplifiers in this set. you are looking at one of them here, covered in a thin layer of dust and corossion after being stored in a damp basement for several years. You can see two places on the top plate, on the far left end, and between the rectifier tube (the largest one) and the main filter capacitor where I rubbed the dust away with my fingers, and was able to produce a reasonable shine out of the chrome-plated chassis. This entire chassis will eventually get buffed to a bright shine. The glass tubes you see in the picture are made by various manufactures. They were cleaned up with glass-plus, and placed on a tube tester. There are also two metal tubes(the black cans) in the back sitting between the two transformers (the black boxes). These are military-grade RCA final output tubes. There were no OEM McIntosh tubes found in either amp. While none of the tubes are audiophile grade tubes, they certainly sounded great upon powerup, and a test-play with Pink Floyd's "Dark Side of the Moon" CD, and a set of Cerwinn-Vega CV12 speakers. Hum was barely detected at the outputs, at less than .01 without a load attached to the output...so it seems like our power supply componets are certainly in good shape! One of the amps had a blown 3 amp power supply fuse, and was replaced.
One problem that did occur though is that after about approximatley 30 minutes or so was the amp that had the blown fuse blew it again! This was done very quietly without any fanfare or sparks, which means a resistor could maybe be out of tolerance (rare for carbon resistors), or a capacitor could be leaky. This is very possible if these units have paper capacitors inside...a very common componet of these days. It is a 3 amp fuse though, and the spec's on the outside say that the amp is not supposed to pull more than 130 watts off the AC line. 3 amps is much more than that...360 watts to be exact...so something is definitely not right!
September 30, 2001
After arriving back
from the Rescue Squad competitions in VA beach, I decided to take the bottom
plate off the amps and take a look around, and this is what I saw:
A rather nicely laid out undercarrage with neatly tied back wiring. This is the amp that was blowing fuses. A vertical card holds a multitude of...yep, paper capacitors...and carbon reisistors. From this view, you are looking at 10 paper capacitors mounted on the circuit board. The black, color-coded pieces are acutally capacitors, not resistors. MacIntosh used the better (for the time) bakelite coated ones. A check with the multimeter reveals that several of these capacitors are in fact getting leaky. I want to replace the entire set of paper/plastic capaictors with modern ceramic capacitors, which should last indefinitely, and give excellent tonal quality.
I did not find a schematic underneath the chassis cover, which is frequently common on units of this vintage, but due to the simplicity of these units, and the excellent craftsmanship in laying out the chassis, componet replacment ought to be rather easy. Because these are audiophile grade units, whatever is done to one amp, will also need to be done to the other, even if the componet is still good. This is so tonal quality will be simliar between the two units. Not only will the componets be replaced in pairs, but pairs of componets that will be used, will be checked with a meter to find the closest matches.
A closer view of the capacitiors mounted on the board (yes, these are all cap's)
An extreme close-up of a suspected bad capacitor. Notice the outer wax covering has melted from leaking current, and getting hot. Capacitors should be cool to the touch, even after extended playing. Unless they are leaky, capaicitors typically do not produce any heat on their own.
General Information on the amplifiers:
The McIntosh model 30 amplifier is an audiophile grade monoural amplifier producing approximatley 30 watts RMS into a 4, 8, 0r 16 ohm load. Impedance can be matched by simply connecting the speaker load to the proper screw terminal on the output bar. Input impedance is a standard 600 ohm, 500 millivolt "line level" with adjustable gain via a control knob. The beauty of these amplifiers is not in what they contain, but on what they DON'T have. What I mean by this is that these amplifiers were engineered to have as few componets in the signal path as possible. This minimizes distortion and coloration of the sound...A concept that many electronic engineers have seem to forgotten in new equipment!
VACUUM TUBE LIST:
6L6: final audio output
5U4: power supply recitifer
12AX7: phase inverter
12AX7: input buffer/ input preamp