Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
You probably want to put some negative volts on the control grids, either by really applying negative or by putting resistors in the cathodes. The negative has to be relative to the cathode so you can achieve it by making the cathode a few volts positive while keeping the grids at ground potential.
I would suggest you are extremely careful with screening when dealing with such high gain and you might need a 'neutralizing' circuit on each stage (a kind of negative feedback) to keep it stable. When you put a tuned circuit in the grid and in the anode, the internal capacitance between electrodes can be enough to make it oscillate. A four stage oscillator would be a nightmare to debug !