Question to tuning of a very old Bb Helicon

[Dean E]

Two weeks ago I bought an very old 3v helicon, Van Engelen, Liers/Lierre,
Belgium. I think 100 - 130 years old.
I was astonished at the 3rd valve sounds not like 1+2nd valve. My chromatic tuner shows for the 3rd valve c# and f# instead of d and g.
.d and g works well with 1+2nd valve.
Did anyone hear of that?
If one knows that, the heli is playable.
Uli

A similar situation was discussed recently in this forum under the topic "helicon with odd 3rd valve"
viewtopic.php?t=6041&highlight=

[Art Hovey]

Apparently this was common in 19th-century French instruments.
Paul Bernard's "Methode Complete" for tuba, bass trombone, & Saxhorns, published by Alphonse LeDuc describes the long third valve system, and contains extensive fingering charts for instruments with 4, 5, and 6 valves. My copy says copyright 1960, but it appears to be a reprint of a much older book.

Also, I seem to recall that Arban's original cornet book described the long 3rd valve system. Most old top-action tubas and euphoniums have 3rd valve slides that can be pulled out far enough to function as two-whole-step valves; apparently there was a time when people wanted it both ways.