This latest project was another ST70 amplifier. This time I decided to build it as originally designed with just a few minor changes. I started with a new stamped metal ST70 chassis aquired on eBay. I sent the chassis to a local plating outfit and had it copper plated to a bright mirror polish.
The PCB is the original circuit but a quality board made with modern materials from Vintage Electron. I loaded the PCB with all 1% metal films, silver micas, and Auricaps. The PT was the PA060S from Uncle Ned as was the filter choke. The filter cap was the same 80/40/30/20 I have used before. I had originally planned to use Uncle Ned's OPTs also but they were out of stock so I secured a set of NOS Dynaco A470/454326 on eBay. They have plastic leads and I suspect they are the later ones wound in Japan. I also bought two NOS RCA black plate 7199s and a Mullard GZ34 (with hole in guide pin). I wired the amp per the original manual except with increased filter capacitance. I used the capacitor in 30/80/40/20 configuration to be on the safe side (thanks to PSU Designer II).
How does it sound? Well it sounds great. I wish I had a bigger room so I could crank the volume more. I swapped a set of Sovtek 7199s and 5AR4 in for the NOS tubes and didn't notice any diminished sound although I think I like the RCAs and Mullard better (could be the price I paid). I CAN tell you that the tubes reflect great in the high copper polished chassis with the lights down low.
I have satisfied myself that the venerable ST70, as designed, with good components can hold its own against rebuilds with designer driver boards.