& Selection Procedures
Because of the extremely high amplification factor and wide bandwidth
of Hi-Fi audio systems, tubes used in such systems must be selected and matched to a far
higher degree than almost any other use for which they were intended. The average,
the shelf tube is more often than not, useless for operation in the earlier stages of an audio
system. With many of the later production tubes (when dies and maintenance of
tolerances got looser and looser) an entire case of 100 tubes may only have 10 or 20
good non-microphonic tubes. The only way to properly test a tube for
microphonics is by ear. At V.T.S. rather than put noise and mic. together as a general
rating they are separated. As there is no place for electrical noise in an audio
system any tube with electrical noise above its thermal noise floor is immediately
That leaves microphonics, the tendency of a
tube to pick up mechanical vibration and act as a microphone.
SMALL SIGNAL TUBES
At V.T.S. all tubes are tested for microphonics including power and output tubes. Small
signal tubes (12AX7, 6DJ8, 6SN7, ect.) are selected by myself using a combination of,
(A) Very special, custom made, ultra low noise
floor, auditioning and measuring units.
Both vintage and current, commercial Hi - End gear.
Using this equipment small signal tubes are separated into four
categories reflecting the job they do in a system. In a system using a low output moving
coil cartridge the amplification factor can run in excess of 100.000 by the time the
signal reaches the output of the power amp! It is very important to get this
selection process right and this is one of the reasons this company was founded. (because
no one was/is doing it right).
Each small signal tube that is distributed by V.T.S has a colored dot
on the base or vacuum tip. This is enamel paint with an estimated 100 year life
expectancy on the colorfastness so it won't rub off! The system is,
Recommended Circuit Type Use
Circuit Gain Use
RED = Low Mic. LINE level tube...
= ULTRA LOW Mic. LINE level tube
GREEN = Moving Magnet PHONO input tube.
BLUE = Moving Coil PHONO input tube
Note: The colors do not designate the quality of a tube only the Mic.