The Mullard developed EL34 introduced in
the early’50s was a remarkable achievement.
Powerful, efficient, with high gain, just what was
needed in the post war boom of hi fi. Today there
are hundreds of thousands in use worldwide.
Unfortunately like all Pentode valves the sound was
not acceptable for hi fi until the "Ultralinear" or "UL"
transformer was developed (half pentode half
triode) to improve the harsh grainy sound quality,
and that situation remains today.
Although "UL" is a good compromise for sound quality and
power, feedback from customers tells us that pure triode
operation is preferred where amplifiers have switchable
UL/Triode mode. As this is closer to the low distortion near
sonic perfection of the 300B/845 etc vintage pure triode
valves, but to make the change you would normally have to
change your amplifier at great cost, as these primitive
valves are "directly heated" and have several design
problems to overcome, not least being prone to "hum".
So Icon Audio have developed the EL34D (D for triode) an
EL34 compatible valve but with all the characteristics of a
vintage pure triode Which can be used in virtually all
existing EL34 amplifiers giving 100% PURE TRIODE
sound instead of 50%.
The EL34D retains compatibility in nearly all amplifiers
where an EL34/KT66/6L6 (even KT88/6550 in some
circumstances) would be used. Normally a straight swap
and bias check is all that is necessary. Icon Audio performed
extensive tests in all kinds of situations where EL34s may
be used. E.G. in SINGLE ENDED, PUSH PULL, SELF
BIAS and FIXED BIAS types of amplifier, both vintage and
modern, integrated and mono block. (Icon Audio ST40,
ST20SE, Leak TL25 and Stereo 50/60, QUAD II etc.)
How is it Different? Unfortunately it is not just a question of ignoring or
removing the 2nd and 3rd grids, the EL34 will not function
without them even in "triode mode". So a total re-design
was called for using a 300B/845 style flat anode with the
critical shape and spacing to get the EL34 characteristics.
What are the advantages? Smoother more transparent, like a veil has been lifted
away, revealing more macro detail and natural sounding.
It’s like changing from cotton to silk. The EL34D is
handmade to the highest standards in Europe and like for
like should outlast a standard EL34 as it is less
complicated and does not have the G2 grid which is a
common cause of failure in EL34s and all pentode valves.
And if you take into account the cost saving of changing
your amplifier this can represent very good value.
What are the disadvantages? None other than a 3db loss of power which you may hardly notice. And you can always revert back to your
standard EL34s for more power if you need to.
Because the EL34D is simplified, any switch becomes
redundant as the EL34D is operating in pure triode at all
times. The EL34D is a "true" Triode. And therefore behaves
the same as 300B/2A3 and other pure triode valves.
To use the EL34D your Leak amplifier, just insert it, the UL connection is ignored, so they can
only work as pure triode valves with no modification.
That is also true of virtually all "self bias" (auto bias) amps
including the QUAD II etc. For fixed bias amps the bias
should be adjusted in the same way as a new set of valves
to the same setting as EL34.