In response to Christian Tedesco asking about accordion registers
on Hooghuys organs, I can verify that LH620 does have an accordion.

LH620 was the last organ built by the Hooghuys firm before the Great
War. An inscription found inside the xylophone valve assembly reads,
'August 18, 1914. War in Europe. Belgium, France and England against
Prussia. The German barbarians will be clobbered. Long live Belgium.'
During WW2 the organ was in a restaurant used as a meeting place for
the Vichy and so was spared being vandalized by occupying troops.

LH620 was built with an accordion located behind the flute harmonic
register in the organs belly. The accordion requires a pressure reducing
bellows because it operates on lower pressure. This resembles a cone
reservoir used in theater organs.

After WW2 the organ was sold for use on the fairground and the accordion
was replaced with German pipes which did sound similar and gave more
volume. When I restored the organ I replaced the German pipes with an
original Hooghuys accordion given to me by Mark Hooghuys. The 'Melodion',
as I call it, has two reeds per note and does sound very nice.

The missing pressure reducing bellows I made using detailed drawings
and pictures supplied from Clophill, England's Ted Bowman who has LH595,
another great Hooghuys organ also with a 'Melodion' and a very rare piano
register.

There are several YouTube recordings of LH620 and at least one recording
of LH595 that can give you an example of how they sound.

Bill Nunn - It's starting to thaw here in Minnesota!
Medina, Minnesota

 [ Hear Bill Nunn's 77-key Hooghuys organ LH620 play "Lady Slippers Rag"
 [ at https://www.youtube.com/watch?v=dwk5yQlgHWY -- Robbie