B.T.H. variometer crystal set
B.T.H. variometer crystal set, made by British Thompson Houston Co. Ltd in 1922; in wooden cabinet 11 1/2 x 5 x 8 1/4 ins. Serial no. R774, type C
B.T.H. variometer crystal set, made by British Thompson Houston Co. Ltd in 1922; in wooden cabinet 11 1/2 x 5 x 8 1/4 ins. Serial no. R774, type C