Duelund Capacitors??

Agreed. Based on our experience with Jensen aluminum vs. Jensen copper (Jensen is the OEM for Duelund), copper foil is the way to go.

We have, in fact used the Duelund VSF copper foil and can highly recommend it. If you're on a budget, forget the Duelund aluminum and just use the regular Mundorf MCap Supreme (not the silver/gold/oil versions), which is almost as good as the VSF in copper.

The Duelund VSF Copper is currently used as part of a loudspeaker x-over. It's the only cap that's directly in the signal path, making it very easy to evaluate.

The Jensens were tried in several circuits, including as coupling caps in a tubed phono preamp, output caps in a tubed active line stage, and as a driver tube's cathode to ground bypass in a 300B SET amplifier. I can't remember if we ever tried them in the x-over.

The Jensen aluminums made the components almost unlistenable. By contrast, the copper Jensens were reasonably smooth and pleasant. In the electronics, we ultimately preferred the VCap TFTF Teflon.

Based on that experience, we didn't bother with the Duelund aluminum and went straight for the copper.