What tubes for ST-70

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).

Ok i put in a quad of the Svetlana EL-34 winged C, RCA 7199's and a GE GZ-34. The sound is alot smoother overall. I do think i lost a little bass when i installed the EL-34's. This leads me to belive the old tubes were KT-77's. The soundstage is a little wider and higher. The top end is more layed back and not harsh at all. I think i'm going to get the Mullard GZ-34 and see if that makes a differance. Over all i'm pretty happy with the sound, just looking for that last little bit.

Your going to find that the KT-77 has a faster, more aggressive bottom end vs. the EL-34. This is also true with the MK-3 amps when the 6550 is replaced with the KT-88. You will also get a bit more power output out of the KT-77 vs. the EL-34. When I had Mk-3's I would also keep them in Genelex KT-88's. That was a while ago when they were still available and reasonably priced. G

I've seen some good things about the remake of the Gold Lion KT-77's. I may try a quad of those next. I've seen them priced around $180-$200 a matched quad. I wonder if they are worth it though?

I have not tried them or tested them so I could not say...G