[Oldtimer74]

I dont think it is the valve as it works OK on SW and MW. Still think problem is in the RF circuits on LW. The pic does`nt help much. Can you check that the local oscillator is working on LW? Either by listening for it on another Receiver (frequency will be 465 kcs higher than the signal or dial reading so on 198 kc/s it should be around 663 kc/s) or by checking the grid current by putting a 1 ma meter in the bottom end of the grid leak. No grid current no oscillation. (Alternative would be to measure the anode current and see if it changes when you short out the oscillator coil).
You certainly should not need much of an aerial to receive a reasonable signal on LW. Most sets using those sorts of valves will receive several stations on LW with only a few feet of wire. Indee I would expect it to be acceptable without any aerial.