AEA LA-30 HF AMPLIFIER (VECTRONICS HF-600, VIEWSTAR PT-1000)
A MODIFICATION AND OPERATING MANUAL
See the differences.
LA-30, an extra thick wire.
A RF current from the variable capacitor C26 doesn't arrive at the valve socket via the shortest route. It is possible that with other amplifiers too, this will lead to instability.
A direct connection from the variable capacitor to one of the grid pins at the bottom of the tube will prevent this and may increase the output on 10 m. You can use an insulated wire through a hole in the frame.