Monthly Archives: March 2016

More McIntosh

Finished up all the resistors on the boards.

power amp

Quite a lot of work involved, picking the best of the best for a good match.

what a mess

Redid the transistors on the boards also because they were a mix-n-match. Not matched, but all from the same batch and things are better. Got a capacitor list in and also the parts needed to make a transistor matching network.

boards

Seems to have been worthwhile. Hooked it up in the living room.

hookup

It really does sound like a decent amplifier (which it is). Now I’m torn- I kinda like having the quad in here!

McIntosh review

Took a bit of a while to get everything apart but managed to undo the thing from the case. The unlocking mechanisms were all jammed up.

unboxed

It was last certified to be good in 1975.

tag

Inside, modular design, a bit rusty and dirty, missing the top shields, all the mounting screws missing.

top view

It’s been worked on a fair bit in the past. Someone rather talented with a soldering iron stuffed this NPN into the socket then threw solder at it from a few feet away.

npn preamp

Pulled all the boards out and started to wipe it down. Then took a picture.

dirty chrome

Little bit of surface rust, but overall in fairly nice shape.

shiny chrome

Helpfully, somebody has removed the base at some time in the past and not put it back on. It does slot back into the cabinet and stay put, mostly.

base

Brought it up gently on the Variac. No smoke, sparks or anything untoward.

variac

Pulled the front off. Unfortunately it got rained on and the front panel started to peel off. The bulbs have been replaced with the wrong type also.

bulbs

The fascia has a thin transfer sheet stuck to it. The water had gotten in under it and caused it to ripple and wrinkle up.

face

Attempted to squeegee the water out and get it to sit flat. It kinda worked.

squeegee

Brought it up with a pair of sacrificial speakers. Thought the preamp wasn’t working, turns out it needs to be jumpered into the main amp.

speakers

Cleaned the cabinet with oil soap, then carefully rubbed it down with 000 wire wool and re-oiled it.

tung

Started measuring resistors and began replacing ones that are out of spec (+- 10%), trying to get within 2% for the replacements.

phase shift and regulator board

Quite a busy workbench. Table. Whatever.

workshop

All but one of the resistors on this board (20V Voltage regulator and 180 degree phase shift) were bad.

new resistors

A number on the right hand preamp board were also bad.

preamp

Buttoned all back up again, looking mostly respectable. More to come.

Exhausting

So.. we left off here with the exhaust system on the car, a temporary stop-gap just to fulfill a purpose.

side exit

Fuel economy and low-end torque were poor. Plus it was really loud. I bought some Meccano pieces of exhaust to build something new.

pieces

Built up a new section, exiting more or less where the original tailpipe would have been, in a similar style.

pipe

Clearance is a bit tight, due to off-the-shelf bits being used (a 90 degree, a 45 degree and some straight bits).

squeeze

Ultimately it looks quite tidy. Mid-range torque is greatly improved. Shall see how fuel economy is.

tidy

Almost factory. Nice. Might get a muffler for it at some point. It has a baritone rumble at low RPM but gains a real loud snarl over 2500.