I am the person who introduced the idea of using 6922/ecc88 family tubes in mhdt DACs, in the head-fi forum. As stated you need an adapter. I took a flyer on the idea after experimenting with every 5670 compatible variant tube. There were certainly great and meaningful differences among them but I evaluated the trade-offs between them as too constricting. Happening upon an adapter lit the bulb.
It's surprising that it works so well, because in the mhdt DACs, that output buffer position has the 6922 operating with a B+ around or slightly under 25v. Very unusual. But sometimes that works and in this case you give up nothing to get plenty. Going back to Havana Balanced ten years ago, through Atlantis, Pagoda and Pagoda Balanced, my preferred 5670-compatible tubes were Bendix 1964 production 6385, and Bendix or Hytron 2c51. The Tesla NOS equivalent was in the same realm. They pushed these DACs to be meaty, vivid and natural. But something was given up, a little, in elasticity and nuance.
The ecc88/6922 delivers everything good about the best 5670 compatible tubes, gives up nothing, then adds more. You'll hear big gains in soundstage dimensioning. Music is dynamically unleashed, spatially liberated and tonally more authentic still than what you expect from mhdt. Bass is deeper where appropriate, more fully realized and textured. In voice you hear more of the whole human pipe, less restriction to the throat. The whole presentation is harmonically more complete, vivid yet relaxed, natural. I use CCa and CV2492 tubes. Siemens and Valvo NOS 6922 work well too.
Phil
