Probably this device has more parts , but indeed it is one of the best output amplifier. It has no problem.

It can gives about  400w  near 28MHz. The sound level is very high.  The modulation level  can be adjusting easily by using the 10K pot. Speak to the microphone, the voice will burst in the channel like a thunderbolt.  The pot solves many problems. It controls, modulation and output power level.

The tube is made of glass. If there is something going wrong, the anode will begins to go red.Than it is time to adjust something .It means that the lamp is a safely place. 

The tube 829 needs less cooling. It is enough  a small blower, or a ventilator.  829 is a VHF double tetrode. You must do it only one tube Connect the same terminal to each other. The American approach to twin tetrodes was to put two separate valves within  the single envelope. Only the cathode is common. You can find  the tube information at this address.

http://www.nj7p.org/Tube4.php?tube=829

You can place the valve 4X150A, 4CX250B, 7034 instead of 829. They give more power than 829, but needs a perfect cooling.

Disclaimer: WARNING    DANGERS. By law and  the high voltage, DON'T BUILT THIS DEVICE UNLESS YOU ARE LICENCED .   I DON'T ACCEPT ANY RESPONSIBILITY OF DAMAGES DONE TO OTHER PEOPLE OR YOURSELF WITH THIS DEVICE. IF YOU WANT TO BUILD IT YOU MUST ACCEPT THIS CONDITION.