Power Pentode
The JJ E34L has a slightly higher grid voltage rating
(-13.5 to-16.5 vs -10 to -13.5 volts) than the
traditional EL34 vacuum tube. The blue glass is purely
for aesthetics. For the same idle plate current value,
the E34L is typically biased with a more negative grid
voltage than the EL34. This allows the E34L to offer
more headroom (later breakup) than the traditional EL34.
Preferred Substitutes ......... EL34, 6CA7