The oscillator is un-tuned so the only tuning procedure required is to select the band (coil tapping) and peak it for maximum RF output. The valves used were selected because they had B7G bases and were the first I put my hand on when I reached into my junk-box. Virtually any pentode valves will work in this application. An EL84, for example, will deliver over ten watts in this circuit but the valves quoted will deliver seven watts from 3.5 to 30 MHz. If you should use another tube then don’t forget to check the screen voltage. If it is less than 250v then you will need a resistor in the screen supply to the valve.
Read source: http://w1.859.telia.com/~u85920178/tx/2tubetx.htm