This should be an extremely simple modification but unfortunately is not working! All I'm looking to do is to switch between two pairs of diodes: germanium and zener. On the schematic, the cathodes are common to each other while the anodes are connected to R9 and R10. Using a DPDT ON-ON switch, I drew up and implemented this switching scheme but doesn't work at all - anyone care to double check that this is correct? It works with a pair of diodes in the stock configuration minus the switch. Going mental over here! Much appreciated!!