What tubes for ST-70

If you purchase your output tubes from Kevin Deal: you'll never have to worry about getting "stuck", in ANY sense of the word. He's first class, all the way: (http://www.upscaleaudio.com/view_category.asp?cat=86)

I don't think you will be disappointed! =8^)

You WILL hear a difference by replacing the GZ34/5AR4 w/a Mullard 5AR4(unless there's already one in the unit). Any improvements in the power supply will be very audible. Sylvania and Phillips ECG 7199's are the two cleanest(least colored) brands that I've tried in the ST-70's that I've worked on. Ditto- the Svetlana EL-34, from the St Petersburg plant(all that's now available at a sane price). If you're considering mods: Contact Joe Curcio (http://www.curcioaudio.com/) Here's been a major player in the Dynaco mods business for decades. Upgrade that pitiful AC cord too.

Circuit topography hasn't changed much at all and the ST-70's came with excellent output transformers too(very important). The major differences in sound that can be appreciated with later designs comes from the improvements in passive components. Replace the old Black Cat coupling caps with some good polystyrene/polypropylene and foils(ie: auriCap, MIT, DynamiCap or WonderCaps) and the carbon composition resistors in your signal path with precision metal film resistors(Vishay or Caddock), and you'll understand SOME of the improvements. I won't even mention the cheesy RCAs, speaker terminals and power cord on the ST-70(OOPS- I guess I did after all).

In this case- it's a pleasure to say, "I told you so!"(re: the Mullard in the power supply) If you're handy with a soldering iron, replace the Black Cat coupling caps with something newer(auriCap/Multicap/DynamiCap to list a few good, reasonably priced ones), and you'll find even more music hidden in your discs. Enjoy your tunes. =8^)

If it's using the 7199: It's probably still the stock design board, and the signal path components are on top(no need to open it up). Solens are way better than the oldies too. Happy listening!