The 17BF11 is a pair of dissimilar pentodes in the Compactron range. We cannot see the makers name but the word Japan appears below the Type designation. The style matches the 6BN6 from Hitachi.
Pentode two is a dual control type for FM TV sound demodulation and pentode one is the audio output valve with up to 2.4 Watts of output.
The main picture shows the end view of pentode two. G3 is close wound and acts as a second control grid. Electrically this pentode is similar to the 6DT6.
The output section is on the right and in actual construction is a beam tetrode.
The beam tetrode face view, with the etched lettering on the glass.
The Type designation enhanced.
The wide glass tube envelope is 29 mm in diameter, and excluding the B12C base pins is 56 mm tall.
Reference: Data-sheet. Type 17BF11 was first introduced in 1964. See also1964 adverts.
