PowerTube Radial 500 Series

Tube Preamplifier

High voltage 12AX7 tube drive with 60dB of gain
Smooth sounding Jensen Transformer input
Hand inserted 100% discrete class-A electronics
Single wide module fits all 500 series rack formats

http://www.radialeng.com/powertube.php

No info about availability.

$700
1 Slot PreAmp