I made a preliminary design effort using a Mu-Follower type layout for dead-quiet PSRR and low noise, and also chose a low-voltage tube. I will be using either 6922s or a 6GM8.
Decided on separate power supply and preamp chassis, for even lower noise, because this is a really low-voltage input signal (old magnetic cartridges etc.).
I enlisted the boy to help me with the power supply. I took a standard but nice-looking metal box as a base.
The boy loves these special wire-strippers. He thinks they look like Oscar the Grouch, and calls them the "Eyebrow tool":
I happened to have a ready-made 60 volt filtered supply PCB, loaded and tested. All that was needed was a 12 vAC transformer. Well, I ordered one on Ebay (notice it says right on it TRANSFORMER). I assumed the housing was just shielding and a convenient mounting. This turned out not to be a transformer at all, but a DC power supply containing a transformer! Who knew! Idiots.
Well, pressing on, I got some four-wire shielded cable and attached a nice solid connector to it. This will go to the preamp chassis proper. I improved the HV insulation inside the plug by weaving electrical tape between the pins.
For tagging purposes, (and additional isolation), I re-paired (no pun) the wires so that the heater (which doesn't matter is two whites, and the HV (60v) is blue/orange (-/+). Keeps things simple to hook up correctly.
Here's a sneak preview of the other half of the project: My part collection for the preamp itself. I'm using this nice knick knack box as a base, it looks really nice. It will have two tubes on it, and some RCA jacks, and a pwr connector.
Not a lot to remark on schematic-wise so far. Will discuss circuits in following posts.
