RIAA Phono Preamplifier Kit Using 6418 Tube

Overview

The project is based on 6418 Tube as it creates a RIAA Phono Preamplifier Kit since the tube is suitable for moving magnet cartridges.

Details

The 6418 sub-miniature pentode valve/tube are considered to be very microphonic but can be reduced significantly by using two tight fitting rubber grommets on each valve in this project. Prior to soldering the grommets to the PCB, they are placed on the tubes. The type of PCB used is double sided, silk screened, and solder masked. It provides shielding by grounding almost the entire top layer of the PCB. The passive components are very basic like the mix of metal film and carbon resistors, polyester, ceramic, and electrolytic capacitors, to keep the kit price low.

The 6418 tube is used in pentode mode as the preamp circuit is a two stage affair with each valve stage buffered by a FET. The switching frequency is set at around 100kHz and the circuit uses a MC34063A switched mode power supply IC to convert the 5V external supply to 30V. The external power supply is a small 5V switch mode power supply with a universal outlet adapter suitable for 100-240VAC.