Bucking Transformer/ Voltage Reducer for Tube Amps[?!?] UMG you're ruining it!

[audiotemp]

Interesting. On the 5% setting I wouldn't expect it to make any voltage adjustment (trim or boost) unless the incoming is > -/+5% (114-126V).

Could be the threshold is on the low side.

For moderate boost or drop, the most accurate voltage regulation would occur with a switching point equal to roughly one half the available drop or boost. For 120V nominal and 5% drop, the switch point chosen this way would be about 123V (above which a drop of about 6V would be applied). Switching has to occur, as you note, at or before 126V.

Realisticaly, there probably needs to be some sort of hysterisis in the switching voltage to prevent dithering, so talking about a single switching voltage is probably too simplistic. But my point is that the highest possible switching voltage (126V) is not necessarily how one can expect this unit to work.

 

[whoaru99]

.. But my point is that the highest possible switching voltage (126V) is not necessarily how one can expect this unit to work.

120 +/-5% (114-126) is the tightest nominal per direct contact with APC.

There may be mfg tolerances, there pretty much always are, but that is the design intent.