I have not seen this before, maybe unique, thort to pass it on.
Developed this to use in my Deltahet.
Any triode will work, The .01 anode cap is to isolate the HT from the resonator, they hate voltage gradients. One caveat, the resonator will oscillate about 5kC above the nominal, use a 450 kC to get 455, a 455 will resonate at 460. Small freq changes , as in very small can be coaxed by fiddling either resistor values or capacitor values.
I developed this to use the triode section of the ECH81 in the product detector of the Deltahet.