After the introduction of the magnificent EC8020 triode in the last post, I'm going to show the assembly process of a LCR RIAA phonostage based on this tube.
In the first part I will show the mechanical construction. It is a pure phonostage, no volume control. It is meant to be used with a separate line stage. It consists of two chassis, phono stage and external power supply unit. Construction is done in the usual style: 4mm anodized aluminum plates which carry all the parts. These will be mounted into wooden frames. Here a photo of the plates before construction begins:
The circuit is two stage, all transformer coupled, 600 Ohm LCR RIAA between them. Both stages use the EC8020 tube.
Since the small pates are electrically isolated from the main chassis by the rubber elements, a wire is added so that all metal parts are grounded. Otherwise the isolated metal plates could pick up stray fields and cause hum.
The next photo shows the main plate with all parts mounted. LCR RIAA modules in the front and 4 old stock paper in oil capacitors, one of them for each tube stage. The caps are manufactured by a company called Filtron. I found these to be superb sounding and just the right fit for a EC8020 phono stage.
The two black connectors are separate jacks for signal ground and chassis. With the switch in front of them both can be electrically connected or left unconnected. This gives maximum flexibility to adjust the grounding to any system configuration. Some turntables have separate ground wires from the disc platter which can be either connected to signal ground or the chassis terminal. The signal ground terminal is normally used for the tonearm ground wire.
The underside of the plate, everything ready to start wiring: