Make sure your highly modified Stereo 70 does not include a solid state rectifier with a lot of filter capacitance. Unless there is some kind of ramp up circuit, that's a sure way to damage the secondary side of the power transformer in a hurry. I already have one on the floor of my office where someone 'modified' their amp only to short out the winding of the transformer. Regarding tubes, I would try a different EL34. The EH's might be the problem. Just understand that if the tubes, or the updates are new, that will take time to break in. Normally output tubes can take 20-30 hrs. to break in. That does not mean to leave the amp on 20-30 hrs. Just keep listening to it when you can, and the sound will slowly change as things break in.
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