[FloridaBoy]

Originally Posted by Rosco65

I own one of the first PSE’s. As soon as it arrived I sent it back for the then-new IIPS mod. I did not listen to the amp prior to installation of the IIPS.

During transients the four output tubes of the amp can draw quite a bit of current. This can cause a momentary drop in B+ voltage. A rectifier tube is good for smoothing this transient and providing good overload characteristics. However, this imperfect rectified DC plays havoc on the grid supply. Even with the zener diode string we experience some unwanted ripple/distortion, which gets magnified at the output.

Dennis’s IIPS mod replaces the rectifier tube in the circuit with SS diodes. This provides more instantaneous current, at the expense of “tube sound”. The rectifier tube is relocated in the fire unit to the grid supply. It now serves as the first [tube] diode in the regulated PS string. It now functions as a DC-DC rectifier, further smoothing the grid supply while buffering it from changes in the B+ supply. Additionally, we would expect to see some tube buffering of the B+ supply from the tube as well.

I do hear changes in rectifier tubes in my amp. It will not be as dramatic as it would be without the IIPS, but it is appreciable. One point to remember is that the rectifier tube is no longer passing a lot of current, and some tubes may sound better coasting along than others.

I find that to be the case with my PSE too.