A low voltage (12v DC) all-tube (12DS7) headphone amp described by Ron Quan and laid out (and enhanced a bit) by Mark Smith, @SmittyHalibut.

There was a category of vacuum tubes called “space charge tubes” which were designed to provide usable power at 12v DC for use in automobiles. The 12DS7 is one such type of tube, another common one being the 12K5 (*).

This design is an all-tube (no “hybrid” FET after the tube, as is common) using these unique space-charge tubes, headphone amplifier that provides useful power into at least 50 ohms impedance (the higher the better) requiring no high voltage as is usually needed for power tubes.

Components are as marked on the board. Use good quality 1% resistors, more for matching between left and right than because of the precise values.

The four 1uF caps that have “3 pins.” Those are just flexible outlines, so you can use 2.5mm or 5.0mm pin spacing on the 1uF caps. The square pad is always used, the two round pads are tied together.

The 12DS7 tubes can be found in a variety of places for about $5 each, such as: Tube Depot, or The Tube Store, or search on eBay for “12DS7 Tube.”

The volume pot can be any of: - Alps RK27 “Blue Velvet” audiophile pots. - Alps RK097 “Green Blob” cheap-but-still-pretty-good pots. - Any of the common .2" spaced dual-gang cheap pots. Luckily, there are good, inexpensive stepped attenuators in the same form factor.

Headphone connector is a Neutrik NRJ6HF.

The PopStopper components are the same as on my PopStopper page : Relay, and TL7700. (And I’m just now noticing that I screwed up on the IC outline on this board too. You’ll have to fold the pins under the TL7700 to make it fit on this outline. Sorry about that.)

(*) Note that the 12K5 is NOT a plug-in replacement for the 12DS7, but it should be a very similar ELECTRICAL replacement. So if you decide to use a 12K5 or similar instead of the 12DS7, you’ll need to wire it differently into the tube socket on the board. But no other modifications should be necessary.