I've wondered about that . My DX-60 covers 10-80 meters but the matching HG-10 VFO has both 6 and 2 meters on it . The Heathkit transmitters for those bands all seem to have their own built in VFO's , of course I suppose you can use that VFO with other brandnames . Its curious why Heathkit did that with the VFO and not put it on the transmitter .
N7BDY
It's difficult to make, and run well, especially with "kit builders", a 80 to 2 meter transmitter. I'm sure the 6 and 2 meter addition in the HG-10 VFO was designed to appeal to users with other crystal controlled 6 and 2 meter rigs.