VAC PA160 Mk I - Manual (Page 10)

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Phillips/ECG/Sylvania 6550A:
Similar to the GE tube, perhaps a bit better.
Sovtek 6550:
Samples tested do not bias correctly, having insufficient current flow. Not recommended.
With regard to the EL34/6CA7/KT77 family, the following observations apply:
M-O Valve Company/Genalex/GEC KT77 (U.K.): Accurate and dramatic imaging, great nuance, control
of dynamics, sweetness, and bass quality. Quality is surprisingly variable for a premium tube, and
we have had to reject about 10% of the KT77s we have purchased. Most EL34s are more thinner
sounding or less coherent by comparison. World wide supply is limited, although Golden Dragon
has announced a forthcoming replica. Highly recommended.
Golden Dragon EL34: A new version of the EL34 designed in Great Britain and manufactured in China.
A good tube, more open, detailed, and dynamic than the East German EL34. Recommended.
Gold Aero KT77: Depending on vintage this reportedly can be a relabelled GEC KT77 or an EL34 with
the KT77 name rolled onto it. Take care. We recommend staying with tubes that are accurately
labelled.
Russian & German Made "KT77": EL34 variants. Not recommend.
Siemans, EUI, and National EL34 (Germany): A generally warm & midrangy tube with fairly good
detail. May be somewhat bland in some systems. Reasonably reliable. Has also been seen with the
Telefunken brand. Acceptable.
GE EL34/6CA7 (applies to those manufactured in USA by MPD): Robust tube with bass similar to better
solid state amplifiers. Overall a bit wooly sounding. This is one of the large bulb variants of the
EL34, and is actually a beam power tube.
EI EL34 (Yugoslavia): Similar to the East German tube, but inferior in most respects. Has unique exhaust
tip on the top. Poor linearity. Not recommended.
Chinese EL34J (available from Penta, Gold Aero, Richardsons, & others): Good detail and very liquid
sound, this tube may seem a bit soft and bright in some systems. We have been unable to confirm
rumors of unreliability.
Tesla EL34, E34L (Czech) (available from Gold Aero & others): Physically well made. Most samples
encountered have a soft, soggy, warm sound, although we have encountered a very few with a
forward, opaque sound. Not our favorite, but worth trying for a nostalgic sound.