Well, I may not be the perfect person to ask about all this stuff, but MAKE SURE to try triode strapping the op tubes of the '70.

This drops the power to around 15w per channel, BUT with high efficiency speakers that's a killer amount of headroom for symphonic music, and such.

I never liked sound of the ultralinear connected op tubes of the '70 and was tempted to throw mine away. After this minor mod it was a completely different amp.

Also recommended; replace the driver circuit board/parts and also the power supply if you can....there are some really good kit replacements available.

Then further, if you apply the Decware "Hazen" mod to the op tubes, you gain a very noticeable amount of detail, substance and depth regarding the overall sound.

Sounds fabulous with well designed high efficiency back loaded horns (I'm using the decware dfr-65 modified fostex driver) and the oldest style decware csp preamp.

Cheers,
Karl

If it's an older ST-70, you're really taking your chances if you just plug the thing in; especially with those old power supply parts (especially the old can caps), but also the traces on the pc board they used for the driver section of the amp often lift up if you try to replace any parts, and so on.

The old '70 if in good shape can sound way better than you'd imagine, no doubt about it.

K