The Dyna FM3 tuner is a nice little unit which sounds quite good. Like most tube tuners, it's RF performance is not great. It's fairly sensitive and can pull in weak stations, but it is not very selective, as it was designed in a time when there weren't nearly as many FM stations as there are now. So this tuner may have problems pulling in a weak station right next to a strong one.
One shortcoming of this tuner is that the EQ modules in the multiplex section are not designed correctly, and the frequency response is not flat. I have designed some small circuit boards to replace the original modules based on a design by D. Sequerra. These little boards will solder right in place of the original PEC modules.
This tuner like all vintage tube equipment, uses a multi-section metal can cap. These caps will go bad over time, and are getting harder and harder to find. I have designed a small circuit board to replace the multi-section cap and the resistors attached to it. Due to the very cramped nature of this tuner, it does not use the same PCB caps that the other cap-boards on this page use, but rather use smaller diameter PCB mounted caps that are also easily obtained. This board also has provisions for solid state rectification. It mounts in the same position as the metal can cap, and requires no chassis drilling.
Dyna FM3 Power Supply Replacement Board
Dyna FM3 PEC Replacement Boards