Which four diodes, and how are you measuring them?? If you are referring to D10-13, and measuring in circuit with a VOM or DVM, then they will all read ground, no matter how you measure with the DVM.? They are part of the double balanced mixer, so there is always a circuit to ground through one of the other transformers with the grounded center taps.
I do not have a BITX 40, only a uBitx v4 and v5.? These are multi-band versions of the BITX40 design principle, so I might be able to help with theory, however actual measurements will require the help of someone else.
I would suggest that you start with describing the current problem, and some of the background.? The more detail the easier it will be for others to provide accurate advice.
Just suggestions, not recommendations
73
Evan
AC9TU
