ST-70 Output Iron?

[Blair]

Assuming I just go for it and am not trying to build ST-70s that are bridged, but a whole different amp using parallel ST-70 iron, which of these is the best layout? Do I really need to worry about output iron coupling since they are carrying the same signal?

Would these output transformers handle another pair of tubes current to get around 80-90W? I know they are spec'd at both 35 and 70W, but the Triode Electronics replacements state a recommended 80mA per side totaling 160mA per transformer.



Thanks!

Blair

[kheper]

Paralleling is what the mono/stereo switch and connecting the output terminals together do on the st-70, which causes the weird, irregular distortion. See the suggestion below on how to really bridge the st-70 (by connecting the 2 hot output terminals to the 2 speaker lugs, without a ground connection.). Compare that with the manual or the last link, in which Bob Latino explains the paralleling in depth.

http://dynacotubeaudio.forumotion.com/t ... st-70-amps

http://dynacotubeaudio.forumotion.com/t ... mpquestion

http://www.audiokarma.org/forums/archiv ... 97736.html

[Blair]

Hi,

Thanks! I have those flagged already.

The way I plan to do it is a little different. By paralelling the primaries and secondaries for an effective 70W 2,150ohm primary transformer which should leave me with a 8,4, and 2 ohm tap.

I read that most of the issues with the "mono" mode ST-70 is the feedback networks and the two separate driver circuits not "meshing"/summing well.

I plan to do it using a PPP circuit with the EL34s vs. two, almost seep rate amps with the outputs parallel.

Like the last part of this:

http://www.tubecad.com/2005/March/blog0041.htm

Does this make any sense?

Thanks!

Blair