Aging a miraphone with no serial number

[bububassboner]

Hello all,
So you might have seen my ad for an old miraphone 186 I had for sale. It looks like it will get a new home but I'm trying to figure out the age of it and am having problems. This is a miraphone 186 5v cc for the euro market. So it has "miraphone waldkraiburg exklusiv" on the bell but no serial number under it. It has S linkage on all five valves. No adjustment screw on the valve caps. Something I noticed on this horn that I have never seen before is that the bell is made with a triangle seam like old Alexander tubas. With this description how old would you guess it to be? I'm guessing with the triangle seam it's got to be one of the older ones but without a serial number I have no idea. Any guesses?
Thanks in advance

[bububassboner]

Here is the ad that I had up too

viewtopic.php?f=4&t=67669" target="_blank

[bort]

What a great looking tuba!

You should email Miraphone about it -- they are always extremely helpful and responsive in answering questions about their tubas, including older ones.

[Ted Cox]

Miraphone began using serial numbers in 1960. If there isn't a serial number to be found, I would guess the tuba to be made prior to 1960.