Holland Made Philips SQ E180F 6688 tubes. Triple Mica gold pin construction!
6688=E180F 10,000 hour 9 pin broadband pentode. Recommended for:
Nobsound- here is a link to a video made by one of our customers after he received his matched pair for his Nobsound headphone amp:
Supratek Chenin Cortese preamp
Yamamoto 06-3 2010
$29.99 per tube