This 6GW8 was made in Germany for the American re-seller International Servicemaster. Uses were in domestic radio and audio equipment. Normally in single ended output stages for radiograms and tape recorders. The design proved popular in low cost stereo systems and was made by several companies, the Philips / Mullard name is the ECL86.
The bold lettering is the word International with Servicemaster below. The single triode is effectively half of the ECC83 design.
The pentode section. The beam plates can be seen inside the anode. The grid support visible is for the screen grid. Another pentode made as a beam tetrode.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 70 mm tall.
References: Data-sheet, 1040 & private communication. Type 6GW8 was first introduced in 1961. See also1961 adverts.