The Apex Peak, with Volcano power supply, is an upper mid-priced headphone amplifier (and also a preamp for those interested in a larger system). It is U.S. made, and uses a 6SN7 tube. The design is also modular, so you can start with just the Peak amp (at $1395) and later upgrade with the Volcano power supply ($700).
The Peak is a hybrid amplifier, using a vacuum tube voltage amplifier stage with a class-A single-ended MOSFET output stage. The idea here is to optimize the linearity of the tube and leverage the MOSFET for excellent drive capability and deep bass response.
We tested only the $2095 combination of Peak and Volcano. The amp was supplied with two tubes, a Shuguang Treasure CV181-Z grade A (a $135.00 upgrade option) and the standard Russian Tung-Sol GTB. Other tubes of course may be used, which increases the challenge for the reviewer in characterizing the amp, but gives the consumer potentially desirable tuning options.