preamp Luxman 5c50 indicator has gone red DC offset

Yes, you should have it fixed, but how important it is depends on your amp. If it is DC coupled you should not use it until fixed. If it is AC coupled then you should be OK.

Here’s what it means:

At rest, with no signal, the preamp should return to 0 Volts output (with inevitable noise). Some preamps ensure there’s no steady state voltage (DC) by putting a capacitor in series with the output. However some use electronic servo’s to constantly adjust the output bias. Yours is of the latter variety. It’s usually straightforward to have it fixed up.

The problem is, with an amp that is flat to 0 Hz is that you’ll get DC on the output, which can be anything from barely noticeable to driver or amp melting. It's made a more serious issue becuase, being DC, you won't hear it happening.  It's silent, so very good thing there's a light to tell you something is wrong.

If your amp has a cap in the input then you will probably not have anything terrible happen before you get it fixed. You can measure the magnitude of the problem with a DC voltmeter on the preamp or amp outputs.

Thank you very much

just , by saying

"It’s usually straightforward to have it fixed up."

do you mean it is not very difficult for technician to fix it?

and what outputs should I measure with a DC voltmeter ?

You say "outputs" ; in my case, it is a preamp so there are several inputs and two preamp outputs (to the amplifier).

Should I measure these two preamp outputs?

(and there are also  2 tape outputs, to be exact)

Thank you

Set your meter to DC and measure each preamp main output between ground and positive (center). Ideally there should be no DC on the output jacks.

And could anybody tell me, what would cost to fix the problem and probably to recap the 5c50 preamp?

thank you