McIntosh MC-75 in unknown condition, what do I do?

It would obviously be desirable to run the tubes across a tube tester, but if you don't have access to one I think it should be safe to try the amp without first testing the tubes, PROVIDED that you use a variac or equivalent to bring up the voltage very slowly, as I described. While you do that, look for any reddening of the plates in the tubes, as well as excessive warming of the transformers, and of any electrolytic capacitors which may be on top of the chassis. Obviously, don't go underneath the chassis unless you know exactly what you are doing, or there is an electrocution risk, even for some time after power is removed.

To help the chrome on similar vintage components, I've simply used commonly available metal polishes which list chrome as one of the metals they are suitable for. Such as Noxon, which you can find at supermarkets and hardware stores. There are also chrome-specific polishes, used for automotive and motorcycle purposes, but I'm not particularly familiar with them.

Apply the polish with cloths or cotton swabs, being very careful to get any of it on the lettering, and being careful not to get it into crevices from which you may not be able to wipe off the residue. Then wipe it off as directed.

Regards,
-- Al

Nsgarch,

Of course I can't say with certainty that the tubes are the original units. I can say with certainty that they are Genelex KT-88s made in the UK (as stated on the tubes). The tops appear quite silvery. The sides look to be somewhat brown. I would also like to clean the tubes as it's clear people have touched them over the years and left some finger prints.

The caps for this model are all inside the base. Any suggestions for testing the caps?

I do appreciate the cautionary comments. I have a reasonable amount of experience working with electronics and some higher voltage stuff. However, my classes seemed to have skipped the section on tube based circuits ;)

I'm not sure I have easy access to a variac but I will check if I decide to plug it in. I also will give Terry a call.

Almarg,
The cleaning/ polish plan sounds like what I had in mind. Brasso and lots of TLC.

Here is another alternative. These guys are big on Mac gear.

http://www.audioclassics.com/

Nikki, for cleaning tubes I always use Ronsonal lighter fluid (naptha - the same solvent drycleaners use.) It will amazingly NOT hurt even the fragile white chalky printing on a lot of European tubes like Telefunkens! Whereas anything with water in it will take the labels right off! The labels on the KT-88's are fairly durable. They are probably Gold Lions, correct? -- that's what McIntosh used quite a lot as their OEM KT88's back in the day. Though used, they're probably still stronger than current KT88's are new -- I have a few and they all test better than the new stuff!

If the lettering on the chrome chassis is 80% intact or more, then it's worth bending over backward to save; so I'd caution against using any kind of abrasive cleaner or pad because it will remove the lettering if it's even in the same room! ;-) Terry recommends something that comes as cotton wad impregnated with some chemical that won't wipe the lettering off -- you'll have to ask him.

If you go to his site, you'll see some unbelievable restoration jobs -- amps that have been through fires, etc.