These are EL84EH power tubes in platinum matched sets. The EL84 is the most common low power pentode tube, popularized in early Vox AC30 amps. Rediscovered by Matchless amps and now currently used by nearly every tube amp company. Delivers quick, soft overdrive distortion, great for recording but usually too low volume for live gigs.
Electro-Harmonix's platinum matching process consists of a 24-hour tube burn-in period followed by a bias (plate) current measurement in milliamps.