Kit RIAA Phono Preamplifier 6418
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.
Circuit RIAA Phono Preamplifier 6418
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.