VAC PA160 Mk I - Manual (Page 9)

9
Output Tubes
Your VAC Amplifier can use the following output tube types: KT88, 6550/6550A, KT77, EL34/6CA7,
KT66, 6L6GC. DO NOT MIX TUBE TYPES. Set the tube type switch to correspond to the tubes fitted
and adjust bias level for proper operation.
The standard output tube is the new Golden Dragon KT88, which possess a nice combination of image size,
tonal weight, and openness. By contrast, the Golden Dragon EL34 provides a leaner, sharper sound. The
Golden Dragon KT66 is darker in tone than a KT88.
The 6550 is not likely to show as long a life in the PA160 as a KT88, and EL34 lives may be somewhat
reduced in the pentode operating mode.
The following comments contrast several available brands in the KT88/6550/6550A family:
M-O Valve Company/Genalex/GEC KT88 (U.K.) PRE-1970 (date approximate):
An accurate and sweet tube with good bass quality. Quality is surprisingly variable for a premium
tube. World wide supply is limited. Highly recommended.
M-O Valve Company/Genalex/GEC KT88 (U.K.) POST-1970 (date approximate):
Hard, glaring sound, only fair detail. Not recommended.
New Golden Dragon KT88 (June 1994 onward):
A new variant of the Chinese KT88 developed in Great Britain. An very good tube, close to the
original, great speed, openness, imaging, and balance. The new version (June 1994) is much
improved, particularly as regards reliability. It may be recognized by its slightly taller bottle and
single top mounted getter. Highly recommended.
Generic Chinese KT88 (including ARS, Gold Aero, Ram, Penta, Jolida, etc.):
Actually a fairly good sounding tube. Bass quality somewhat phasey, some mechanical sound due
to a subjective dip in the upper-mid-range. Some samples make rather alarming noises on warm up
and cool down, often heard through the speakers. Reliability is variable.
National NL-KT88-USA:
A new version on the KT88 produced by the US arm of the Richardson's organization.
Visually very similar to the original and sonically satisfying, close to both the original and
the Golden Dragon. Slightly lightweight sound, but sweet. Very expensive.
Golden Dragon 6550A:
A good tube with more subterranean bass and mid-range zing than a good KT88. Loses in terms
of ease and dimensionality. May help wake up a sleepy system, but overall less natural. Good sound.
US made RCA and Tung-Sol 6550:
Early 6550 type in the "coke glass" bottle. Pretty good sound.
GE 6550A (applies to those manufactured in USA by MPD):
Overall hard and lacking in air. Not recommended.