What he said--with 3 nit-picks:

...whenever we start up an older tube radio rig,
we plug it into a large power reostat.
Wise Linux User

Most folks use a Variac.
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We slowly increase the voltage from zero, up to the AC operating voltage
...'Slowly' means a steady increase over approximately 5 to 8 seconds

Very old lytics that have been in deep storage
can be even more temperamental than this.
I have seen (with patience) ancient components (out of the unit
and on a capacitor tester capable of applying variable voltages,
up to the working voltage of the part) come back from the dead
over a period of many, many minutes.
S-L-O-W-L-Y cannot be overemphasized.
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The reason for this is:
1. to charge the paper capacitors, slowly,
so that the possibly dried-out, dielectric wax paper is not breached.

As I suggested above, it's the electrolytics
that are the most fragile of the things in an old unit.
They must be allowed time for the dielectric layer to "form up";
this is an electrochemical process and mustn't be rushed.