I recently received two copper caps, a WZ34 and a W55/175 (supposed to be a 55v drop at 175ma current draw.) I am dissapointed in them. Both have more sag than specified when compared with a Mullard GZ34. The amp is a Deluxe Reverb with GZ34, Dave Allen's oversized PT/OT/Choke set (180ma current!) and JJ 6L6GC. Initially, using the GZ34, I set the bias at 41ma and 428v for 17.5w idle dissipation using the transformer shunt method. I measured a few things, then swapped in the WZ34 copper cap without rebiasing: Standby/Plate/V1, pin 1 GZ34 - 477v/428v/201v WZ34 - 475v/401v After installing the WZ34, the idle dissipation worked out to be less than 12w. This was my first sign that the Weber Copper Cap may not be a direct replacement for a tube rectifier. I rebiased with the WZ34 for 17.5w idle dissipation. The new numbers are: 46.5 ma @ 376v plate, 176v on V1, pin #1. As you see, the WZ34 has an additional 52v of sag compared to the WZ34 under the same idle load condition. While this may be a musically useful outcome for certain playing styles, it does not duplicate the performance of a GZ34. Out of curiosity, I swapped in the W55/175 and attempted to bias for an idle dissipation of 17.5w. I couldn't quite get there due to the values of resistor in the bias circuit. Here's what I found: 43.5 ma @ 363v = 15.6w, 169v on V1, pin #1. This is 13v more sag than the WZ34 with 1.9w lower idle dissipation. Since I can't make a direct comparison with a 17.5w bias setting, I am guessing the W55/175 has a additional 20+v of sag compared to the WZ34 sample I have. This puts it in the neighborhood of 90 volts (17v normal GZ34 drop + 52v WZ34 + 22v W55175) total sag vs. simple diode rectification! And this is with a load that is less than 175ma -- its rated current draw for a 55v sag. These are not the results I expected. The copper cap remains a good idea, but I don't know how to predict the results based on Weber's model descriptions. I suppose through trial and error one could find a version that gives a desired drop in plate voltage and current sag. Perhaps the units I received do not have the correct internal parts to match the specification. I e-mailed the above information to WeberVST. Ted's very prompt response was: "We sell a ton of those with very few complaints. Bruce Collins at Mission Amps assisted me in determining the original values. I also used the nominal drop values as specified in the various tube manuals. Using the official specs from the tube manuals, it is simple ohms law. There is nothing dynamic about the forward transfer function of a tube rectifier. Some GZ34's may actually be better (stiffer) than the nominal specs. Send them back and we will refund your money." There you have it. I gave Weber some objective data that indicates their "simple ohms law" formula doesn't match the real world. They weren't at all concered that both units might not be in spec. Oh well, at least I can get a refund. I had high hopes for their use... Ken PS - The new Allen OT/PT set for the DR kicks booty! See my separate post on that.