05-30-2015, 07:50 PM
Here is data on the 6J8 http://www.radiomuseum.org/tubes/tube_6j8g.html . And here is the 7J7 http://www.radiomuseum.org/tubes/tube_7j7.html . They are electronically the same tube, but based differently, and the 6J8 uses a cap.. Hope it is of help