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Testing & 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, off 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 rejected.   

That leaves microphonics, the tendency of a tube to pick up mechanical vibration and act as a microphone.


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.

       (B)    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,           

                                                   Color                  Recommended Circuit Type Use                Circuit Gain Use
                                                      RED       =      Low Mic. LINE level tube... ………………………….100 X
                                         RED-GREEN      =      ULTRA LOW Mic. LINE level tube………………. 1,000 X
                                                  GREEN      =      Moving Magnet PHONO input tube. ……………..10,000 X
                                                     BLUE      =      Moving Coil PHONO input tube ………………...100,000 X

Note: The colors do not designate the quality of a tube only the Mic. level.

Power & Output tubes are tested a minimum of two times at V.T.S.

(A)  The first test is at the regular rated testing voltage. (Tube testers in general do not run the tubes at anywhere near the voltage and current that amps do).

(B)  The second test is a full ratings, metered torture test at full current and voltage, done with amplifiers to make sure the tubes actually "work" properly (as compared to "measure" properly). Microphonics, noise, and other parameters such as plate and grid heating are also monitored continuously during this test.


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