Tube tales.(Forum)

I would like to impart some of my experience regarding your Surveying the Soundscape section in Issue 97. My experience in this case deals with the Dynaco ST-70 and the AVA rebuild of this venerable piece of audio lore. I have done two of the AVA rebuilds, one with a board from AVA cut and jumped from 7199 pin layout to 6GH8A and another etched for the 6GH8A. The original AVA ST-70 used the old 7199 before AVA and SCC discovered that the cheap and ubiquitous 6GH8A would work.

I used the ST-70 in a bi-amp system and the great thing about the input filtering on the AVA ST-70 is that using equations from the 1983 Audio Basics article, one can modify the filtering. I tweaked mine for 100 Hz on the low end, so the satellites only received 100 Hz up to about 15 kHz. One just needs to fiddle with resistor and cap values in the equations and order the parts. The math-challenged will need help.

I traded the first ST-70 using the old Audio Mart and sold the second one some years later via Audio Mart too. The second one used very expensive paper-in-oil coupling caps and that actually made an improvement (sorry, Frank). The reason for the sale was that my third ST-70, the Welborne Labs mod, far outperformed the AVA ST-70 in ...