Vintage Dynaco ST-70 Modified with DIYTUBE ST-70 Driver Board
35 wpc in stereo and 70 w in mono
Completed in June 2007
The ST-70 is an amp that no tube aubiohobbyists
should live without. This was an eBay find that was in pretty good working + cosmetic condition. However, I wan't terribly
impressed with its sonic characteristics, particularly it's tubby bass and lingering muddiness in mids+highs. So, it was
was time for a makeover.
The chassis was completely gutted and cleaned first with Fast Orange to get
rid of years of organic deposits. The chassis was then polished several times with Turtle Wax's chrome polish, followed
by Blue Magic metal polish, all of which are cheaply avaiable at local discount autopart stores. All tube sockets were replaced
with ceramic octals.
Shannon Park's DIYTUBE ST-70 driver boards are a standard upgrade of the 7199 boards. The tube complement is 1x 12ax7 and
2x 12au7. The design is pretty much a time tested modified Mullard design dating back 50 years. The board allows individual
biasing of output tubes for push pull perfection.
The only thing that's left to be done on the amp is to retube. 3 Svetlana
and 1 Mullard EL34s (Russian productions) are on the power duty for now, and I would like to experiment with 6L6GCs or KT77s.
All in all, the restoration was a great success wiht much improved sonics. It pumps out some serious wattages of pure listening
enjoyment - deep and accurate bass and very forward mids. Great sounding amp!