[Radioroslyn]

If it helps think of it this way. Grid 1 is the control grid for the oscillator(pin5). Grid 2 looks like grid but acts like a plate. It has hv on it and acts as the plate of the oscillator (pin4).
Grid 3 is the control grid for the mixer (pin 8 ). This is where the rf input is connected, antenna coil and such. Remember grid 2? acts like a plate but is a grid which allows the electrons to pass though it. If it was constructed like a plate the electrons wouldn't pass though it they would stop. This is where the mixing takes place the oscillator signal leaking though G2 and mixing with the rf signal on G3. G4(pin4) is the screen grid for the rf part of the mixer. Notice the G2 and G4 are connected together internally. This way hv can be applied the grid the act as the oscillator plate and the screen grid of the rf part of the tube all at once. Grid 5 is the suppressor grid (pin 1 or 6) Usually tied back the the cathode and is pretty much at ground potential.

Another way to look at it is Grid 1,2 and the cathode make up a triode oscillator. Grids 3,4,and 5 and plate make up a pentode rf ampilfer. With some leakage from the osc in the rf pentode it mixes the two signals together.

Simple right????

Terry