Mods for DYNA ST-70, What do you think??

I think soundvalves.com points out that even the stock version has some easily correctable mistakes that to do just a parts upgrade would be a bit of a shame. So at the very least/minimum go their route, along with the better parts. Now if you want to take it further others have presented those options too.

If you do nothing else get rid of the selineum rectifier. Replace it with a diode. These things blow up and take other stuff with them and when(not if) they blow they emitt a toxic cloud into your room!

I did the soundvalves mod ($99 many years ago), with great results....more detail, etc. I also replaced the selenium rectifier, beefed up the power supply with more caps, and parallelled all electrolytics with small value Wonder Caps (you would use MIT caps today).

I have modified several ST-70s over the years and the only stock parts I keep are the chassis, transformers, choke, and bias pots. Everything else (RCAs, quadcap, binding posts, etc.) should be replaced with quality parts. I have replaced the 7199 front end with a 12AX7 front end that Jim Aud of Purist Audio came up with several years ago. Considering it's hard to find good 7199s anymore the 12AX7 front end is the way to go and is sonically superior.

Since you know a lot about the ST-70, I will ask you if it normal for them to have a chasis hum, not audible in the speakers but directly from the chasis? I can hear mine from 20 feet away when the music is very soft.