This Russian-made pentode is standard on many UK amps and has great durability, although as with most Russian power tubes the break up is a bit harsh and they lack high end as compared to the true European models. This exclusive Groove Tubes design is a close copy of classic the Mullard type with good power and flat tonal response. Unique sound, slightly edgy distortion when pushed hard. The most reliable of all in this family. Country of origin: RussiaCountry of origin: Russia