Tube replacement for Dynaco ST 70

First of all, could you tell us about the modifications? I've personally used several different mods of the ST-70 with a number of different tubes. I've recently used Siemens, pre-Sensor Svetlanas, Winged C's, Shuguang Treasures, RCA's, Mullards, and the reissue Tung-Sols. Mullards are usually my favorites, but good matched pairs/quad are just skyrocketing in price. I'm also a big fan of the Siemens; they seem to be a little more neutral in the presentation than the Mullards. I might say that the Shuguang Treasures are the best of the bunch right now. If $200+ for a quad, then I would suggest getting the Winged C's. They're essentially the same as the pre-Sensor Svetlanas which have a very similar presentation to the Mullards.

JJ E34L as suggested above are a well extended and well well balanaced EL34 type that works well in the Dynaco. They can be had for a very good price from Eurotubes.com I like the blue glass versions . I have been using them for years.

I own one of Will Vincent "Audiospec" Stereo 70's.
Recently upgraded the output tubes to the Gold Lion KT66
and have not looked at other EL34 tubes. The soundstage just opened up. With this amp the improvement is huge.
All the best....

I realized I only listed EL34's. If your amp will accommodate them with the mods, the Gold Lion KT-66 reissues are outstanding - probably the best bang for the buck and one of the best 2 or 3 options available.

This is a Will Vincent Mod