I recently came across a box of the Raytheon 717A tubes. A simple pentode synonymous with the VT-269 tube. Though I know it's not good criteria for selection I love their appearance: A smooth flattened bulb with a sideways plate assembly in the middle (picture below). Looking up the datasheets they seem vaguely similar to half a 12AX7 tube.
Does anyone have any experience with these tubes, or possibly guidance/schematics on implementing them in a headphone amplifier? The only use I've seen in an audio amp so far is the Yamamoto A08 and all their products are an order of magnitude over my budget. I can assemble amps but the finer parts of design are far above my skill level.