Hiding the key signature?

[Mark Probert]

Hi.

Another newbie question. How do I hide a key engraver after the first 
instance? I want it at the top, then not on the following staves, which 
is the default behaviour. I'm sure there is a hide.engraver-thing 
somewhere...

--
\version "2.22"

tune = \relative c'' {
  \clef treble
  \key des \major

  \repeat volta 2 { \bar ".|:" R1 R1 R1 R1 } \break % key sig here
  \repeat volta 2 { R1 R1 R1 R1 }                   % no key sig?
  \repeat volta 2 { R1 R1 R1 R1 }                   % no key sig?
}
\score {
  <<
    \new Staff \tune
  >>
}
--

TIA .. mark.