In article ,
wrote:

Yes, you got a lucky find!

I've bought a very nice receiver (a Proton) where the seller said it
didn't work at all, and the reason was that he hadn't read the manual
and seen that the receiver needs a jumper between "preamp out" and
"amp in" if you aren't using an external signal processor. The
original jumpers had been lost at some point and the owner didn't do
his research...

I am a little confused though about the phone switch.
It has the following selections:

MM (Moving Magnet)
47K
100K

MC (Moving Coil)
10 ohm
30 ohm
100 ohm

Ok, I understand what they are saying, but how do I know if my cartridge
is MM or MC, and what the resistance rating is?

Ummm... search the Internet for its part number?

Or, measure its DC resistance with an ohmmeter. If it reads a few
ohms, it's certainly a moving-coil amplifier. If it reads hundreds,
it's probably a moving-magnet (there are some higher-impedance moving
coil cartridges but they're less common).

The numbers you see above are not those of the cartridges... they're
the parallel resistance of the phono stage itself, in that setting.
The frequency response of any phono cartridge will depend to some
extent on the load resistance. The cartridge maker may specify the
recommended load.

This appears to be a real useful thing, but I never even knew there were
different kinds of cartridges. In the past, I just installed a cartridge
and plugged it into "Phono".

Cartridges that you can do that with, are almost all moving-magnet (or
moving-iron) cartridges. The MM setting, and 47k ohms input
impedance, would very probably be the one to choose - that's the
industry-standard resistance.

MC cartridges typically have a significantly lower output
voltage... plugging them into an MM input will result in very low
audio levels. One needs a bunch of additional voltage gain (provided
by the preamp in MC mode, by an external "head amp", or by a signal
transformer) to use a low-output MC cartridge.