I’m feeling a bit guilty about all the time you guys are wringing your hands over my small problem. But I appreciate the quick education.
I believe in retrospect that some sort of voltage spike or impedance excursion occurred as a result of my failing to turn on the speaker’s LF amp before powering the ST-70. That is not to say that there may not be another issue with my ST-70, as I did purchase it used. It biases easily, sounds great on the B&Ws and was professionally assembled by Triode USA. It sports all JJ tubes.
It would be convenient to find a smoking gun here because you may notice the B&Ws have an “Auto - Off” switch; the Auto position is intended to keep you from having to reach down near the floor or remember to turn the amp’s main on and off switch. It senses a signal and powers the amp automatically and after a modest period of silence powers the amp off (standby). I am now hesitant to use it.
The last open item for me is how to rewire the amp for 16 ohm use. The manufacturer is having an apparent staffing issue possibly COVID related. I thought perhaps I could just swap the 16 ohm tap for the 8 or 4, but the 16 ohm tap is wired to the input board. An entry in the manual says it is for feedback. If anyone else has this amp and knows the answer I’d be much obliged for some advice. It will be at least another couple weeks before the Altecs are ready for prime time.
Peter H, I assume the 100 ohm resistor would apply to the 16 ohm tap when I go that route as well? And any particular wattage rating or resistor type?
Thanks again, all.