Have the latest prototype boards up and running.
Major progress and only a couple of minor setbacks.
Have to share some the setbacks. This is audio sausage making.
Couldn't help but notice that after initial power up that the plate power transformer was running really hot. Like too hot to touch hot. Very strange give that the current demand is only a handful of milliamps. After chasing numerous dead ends finally realized I'd installed the wrong relay and was completely shorting out the transformer secondary. We have 2 relays in our parts bins that are same brand, size, color, and pinouts. So of course in my excitement to get the buffer running I managed to pick the wrong one. Space heater - 1 point. Engineer - 0. As a bonus for screwing up the power supply relay the Belleson Superregulator was toast. A quickly assembled LM317 module replaced the Belleson and we were back in business. Now I had hum but only in one channel. Hmmmm. Swapped the tubes and the hum changed channels. Bad tube. Development testing is hard on the hardware.
Despite these setbacks we are 98% done. The last 2% involve some minor rework on the 2 boards to optimize connectors, increase parts clearance between the 2 boards, tighten up the star grounding layout, and just generally dot the i's and cross the t's on the schematics and boards layouts.
Listening to the preamp buffer as I write this. Amazing dynamics. Best audio I've ever heard.
When we're back up and running after the New Year's break, production hardware orders will be placed with the goal of releasing the tube preamp buffer by the end of January. Over the break I'll work on finalizing pricing and set up pre-orders on the website. More on that soon.
The pics below show a close up of the tubes running in a temporary enclosure. The bottom pic is a rough shot of the prototype assembly. Power supply in foreground. Tube board in background laying on its side. Power entry module on the right. Temporary I/O jacks. It's all good!