The Raytheon 5784wb to EF86 Converter allows you to upgrade any microphone that uses an EF86 type tube. The sub-miniature Raytheon 5784wb is widely regarded as one of the lowest self-noise tubes ever utilised in a microphone circuit. Swapping out the original EF86 tube in the Neumann U67 microphone will result in a lower noise floor, cleaner midrange and better definition in the highs.