1Ж42А. As a mixer/Frequency changer????

[Murphyv310]

Just add a second diode, ground is anode, cathode to existing anode.
Or try it with capacitor direct to g1 with a 10M or 18M grid leak.

You can't sensibly have a wide band (entire MW) high impedance RF transformer. It won't work if a 10 mH choke from 0V to diode input doesn't work.

Alternative DC path solution: Wire like a valve detector. Diode across the 18M or 10M grid leak, fed with capacitor from RF amp, thus cathode to 0V. Also try it the "wrong" way round, where it drives g1 positive instead of negative.

In fact the best performance has been placing the diode between the G1's and ground, cathode connected to ground and the RF coupled to the diode/G1 via a 180pf cap, my original YouTube clip had the diode connected that way. Even looking at the RF output on a scope with an X10 probe severely damps the signal and my X20 was never returned after loaning it a few years back.
I'll revert back to the original way once I get the new diodes.

I've actually tried every possible configuration of diode placement over the last week, some increase distortion with better resolution of weak stations but are hopeless on my local others distortion free with lower sensitivity, the above way gives the best overall results.