I'm about to start building this mic and have a couple of questions:
1. Could I use a Primo EM-21 electret capsule for the project? If so, should I modify the build to suit it?
2. I have a generic Chinese PSU in the studio. Can I adjust it for 100V and 6V and use it with the mic? I intended to build the PSU on the board I bought from Milan, but I'm having trouble sourcing the toroid to use with it.
1) polarisation voltage of s52 mic is 50V, electret capsule doesnt need it. Im not sure if its possible join this tube circuit with electret capsule. Search for 'countryman' microphone circuit (- tube circuit with electret capsule and Jensen transformer).
2) yes you can use your psu. For transformer you can check m49 thread. There are some possibilities in BOM. In any case you can use mic with 120V on B+.