[RodB]

Hi John,
The grids of a tube are numbered starting from the bottom grid. Grid one is usually the input or signal grid. Your 6K7 has three grids and the first grid is attached to the grid cap. You'll notice the wire coming out of the first IF transformer going to the grid cap, that is the IF secondary feeding the 6K7 input grid. The 6A8 has 5000 grids (just kidding). Since this tube has a dual function, the first two grids are dedicated to the oscillator circuit and grid 3 is the input grid which is also attached to the grid cap. Most receiving tubes with grid caps have the signal grid attached to the cap. Later 8 pin octal tubes are identical except for the grid cap and have a S (for single ended) added to the tube number as in 6SK7 or 6SA8.