One small tid-bit of supposition is that when Lindner switched tube mechanic horses from a cadry of tube subcontractors like Stobbe(Vierling Specialist), Eckoldt, etc. to primarily Robert Schlegelmilch, that his sub mainly turned out Black & White or maybe S,D. & G. demanded Black & White tubes?? Most Series II Lindners will wear R.S. initials.

Serbus,

Raimey
rse