This class is one of the most interesting SEK / OSE classes and also one of my favourite ones.
They were actually built by various German builders around 1920 - 193X as wood - covered coaches, some of them with 3 axles and the rest with 2 axles, with different - random numbers and classes. Later, in 1954 - 1957 they were rebuilt (of course in Germany) to the known - current form which was called '' B3yg '' (There were also '' AB3yg '' - A and B class and '' BD3yg '' - B class + luggage compartment) and D.B. classified them as 85801 - 90537 (4737 cars !). They were also called ''CONVERT'' due to their rebuilding.
S.E.K. bought 50 of them in 1966, which arrived to Greece around September 1966. They were classified as Βρπτ 401 - 450 and later 50 73 23-20 321 - 370, always been used in pairs (so only even numbers) mostly due to rolling reasons.
Finally in the 1980s, when some of the older maintenance cars had srarted to be ... useless (damaged, old construction e.t.c.), some of these '' B3yg '' were converted again, this time to maintenance car, mostly for northern Greece.
Some of them still exist in various forms ... mostly withdrawn maintenance, and other cars with various ex- uses, still most of the times in pairs.