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On the Merkel 20 Bore form 1977, the tubes are fastened by the >>Weichlot<< method and the rear lug wears the >>Qualitätszeichen „Hervorragende Qualität”<< or 1st Quality / Excellent Quality which was an advertising ploy to counter the dip in Quality after the early 1950s(1952 or 1953 I recall but could be mistaken) Revolt due to inferior base components. To be honest in the German mind they never did recover..... I seem to recall the mark was just only for Exports?

Serbus,

Raimey
rse