Quote:
from the photo I can only infer a rough picture as follows:
single tuned input -> 1/2 ECC85 gain -> double tuned BP -> 1/2 ECC85 gain -> double tuned BP -> 1/2 ECC85 mixer + 1/2 ECC85 LO. Right?
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Please find the updated schematics.
It should be
single tuned input --> E88CC cascode amp-->double tuned BP--->E88CC cascode amp ---->double BP--->1/2 ECC85 mixer + 1/2 ECC85 LO
Now I use both gimmick wires for stage 1 and (0-1pF) piston trimmer for stage 2 of the coupling capacitors. Note that in the ideal bandpass design calculation using Zverev's method i assumed the input and output impedance are identical (symmetrical). In reality, the BF filters have asymmetrical input and output impedance with the cascode and mixer valves.