sales@effectrode.com

  • About Us
  • Knowledge Base
    • Tubes
    • Binson Echorec
    • History
    • Pedals
    • Quality
    • Techie Tone
  • News
  • Press
  • FAQ
  • Vacancies
  • My Account
  • Login
logo
  • Store
  • Stockists
  • Artists
  • Contact
  • | Newsletter
  • Store
    • Accessories
    • Pedals
    • Vacuum Tubes
  • Knowledge Base
  • Stockists
  • Artists
  • Contact
  • FAQ
  • About
  • News
  • Press
  • Newsletter
  • 0

    Shopping cart

    0
    Cart is Empty

Noise

  1. HomeKnowledge BaseNoise

Noise

by Robert B. Tomer (Excerpt from ‘Getting the Most Out of Vacuum Tubes’ published in 1960 but is no longer in print)

Noise is defined as an output signal originating within the tube and is not specifically hum or microphonics. There are several possible sources of noise signals. Whether they constitute a defect depends upon how the tube is used. Hence, noise is considered to be a subjective failure since the actual application of the tube is the significant factor in determining whether or not it actually becomes classified as a failure.

The most common form of noise within a vacuum tube is that caused by intermittent shorts or opens. The nature of these intermittents is such that it makes a big difference how much voltage is applied between elements and at which source impedance, as to whether they exist or not. Also, it is important to define what kind of detection device is going to be used before you can decide whether you have an intermittent or not.

The classic short tester is a neon lamp in series with a voltage source and a resistance to limit the current flow. It is assumed that if an intermittent short occurs, a circuit will be formed and a current will flow. At the same time, the lamp will flicker and the user will know that he has an intermittent short. But will he? The neon bulb is often used in a self -rectifying circuit with an AC voltage applied to it. The voltage required to cause the lamp to ionize is not present during the entire cycle. During a very significant portion of each cycle, the lamp cannot light even if a dead short occurs because the voltage across the circuit is insufficient. Suppose that the voltage is just sufficient, but falling, when the short occurs. The neon  lamp requires a finite time to ionize and fire; hence, if the short occurs at the time the voltage is approaching the critical value there will be insufficient time to record it and it will pass unnoticed.

There is also the matter of nonrepeatable shorts and intermittents. Particles sometimes shake loose from within the tube structure and drop down between the elements. These occasions produce momentary shorts which in all probability will not occur again. Nevertheless, in some pulse-triggered applications, as for instance, in counting circuits, these random noise pulses can cause false operation.

Repeated testing of tubes in an endeavor to eliminate this failure has been unsuccessful. An exact explanation for this involves problems in statistical probability that are not within the scope of this discussion. However, it can be mentioned that the use of a statistical approach to this problem can be quite successful. For instance, if 100 tubes are measured and the number showing momentary shorts is noted and compared with another lot of 100 tubes similarly tested, the lot having the significantly lower number of random intermittent shorts will always show this characteristic, no matter how many times it is remeasured. This means that statistical sampling can be used to indicate the probability of the occurrence of intermittent shorts in future use.

The second and most common form of noise in vacuum tubes is sometimes referred to as “frying noise.” It is most often the result of leakage paths across the micas. The measurement of this characteristic is complicated because it has impedance and frequency characteristics that make a universal test very impractical. For example, there are tubes which will produce considerable noise when tested in a high-gain RF amplifier, but none when tested in a high-gain audio amplifier. The converse is also true. Tubes which produce extraneous noises in an audio amplifier may produce no noise at all in a high-gain RF amplifier. The reasons for this observed phenomenon are not well known. Neither is it thoroughly understood why the relation between the amount of noise detected and the sensitivity of the amplifier used to detect the noise is not a linear function.

Noise in vacuum tubes is a problem which depends almost entirely upon the users’ requirements. It does not lend itself to accurate definition and there are very few methods, if any, by which the user or the designer can protect himself against it. About the only method is to make use of the laws of probability in some way or another. In fact, so many vacuum-tube characteristics resolve themselves into a matter of statistical probability, it is felt that some understanding of this subject is essential before proceeding into some of the other areas of vacuum tube knowledge. For this reason, the subject of characteristic variables and their normal ranges and limits is discussed in Chapter 4.

In This Section

  • Black Plate Tubes
  • Chemical Highlights of Tube Manufacturing
  • Cryogenic Treatment of Tubes: An Engineer’s Perspective
  • Developments in Trustworthy-Valve Techniques
  • Evolution of the Tube
  • Foil Those Tube Forgers
  • Microphonics
  • Mullard ECC83 (12AX7) Reissue vs Original – A Physical Comparison
  • Mullard ECC83 (12AX7) Reissue vs Original – An Electrical Comparison
  • Noise
  • Oxide Cathode Life: Investigations into the Causes of Loss of Emission
  • Signal Tubes
  • Speed, Efficiency & Perfection – Aims That Have Built a Mammoth Factory in 16 Years
  • Steampunk Technology: The Inner Workings of Vacuum Tube Buffers
  • Subminiature Tubes: The Future of Audio!
  • That’s a Sylvania tube, the print is green, no, it’s blue
  • The ‘Magic Eye’
  • The ’12AT7′ Tube
  • The ’12AU7′ Tube
  • The ’12AX7′ Tube
  • The 12AX7 Tube – The Cornerstone Of Guitar Tone
  • The 6SN7GT – the best general-purpose dual triode?
  • The Accurate BSPICE Tube Models
  • The Cool Sound of Tubes
  • The Tube Family Tree – Part 1
  • The Tube Family Tree – Part 2
  • The Tube Family Tree – Part 3
  • Tube Vendors
  • Tubes: The Old Verses the New
  • Vacuum Tubes and Transistors Compared
  • Valve Microphony Part 1: Production of Microphony and Methods of Investigation
logo
+44 (0) 1782 372210 sales@effectrode.com
facebook instagram twitter pinterest rss soundcloud
Newsletter

Useful Links

  • Shipping Policy
  • Refund Policy
  • WEEE Policy
  • Privacy Policy
  • Warranty Policy
  • Register Your Pedal

Instagram

The Blue Bottle™ Inductorized Booster pedal was The Blue Bottle™ Inductorized Booster pedal was custom designed to extract fatter, richer more bluesy B.B. King ‘335’ tones from strat-type guitars.
 
#effectrode #bluebottle #boost #guitar #blues #bluesguitar #guitarpedals #guitarfx #effectspedals #guitareffects  #guitargear #guitarist #knowyourtone #guitarpedal #guitarplayer #geartalk #fxpedals #guitars #electricguitar #pedalboards #guitare #guitarra #chitarra
The Glass-A™ model GL-1A triode buffer is specia The Glass-A™ model GL-1A triode buffer is specially designed to do just one thing very, very well—buffer the output signal from a musical instrument fitted with a high impedance pickups or transducer.
 
#effectrode #buffer #tubeeffects #guitarfx #guitar #guitarpedals #tubepedals #knowyourtone #guitarplayer #notpedalbored #pedalboard #guitartoneisrocketscience #pedaloftheday #effectspedals #pedalboard #guitareffects  #guitargear #guitarist #knowyourtone #guitarpedal #stompbox #guitarplayer #geartalk #fxpedals #guitars #electricguitar #pedalboards #guitare #guitarra #chitarra
All Tube: 100% pure analogue vacuum tube audio pat All Tube: 100% pure analogue vacuum tube audio path operating at amp plate voltages ensures the PC-2A compressor has huge headroom and very quiet, natural sound reproduction. Each tube is burned in for 24 hours and each PC-2A compressor pedal tested and hand assembled by the designer to make sure it is perfect.
 
#effectrode #PC-2A #compressor #compressorpedal #pedaloftheday #tubeeffects #guitarpedals #guitarfx #effectspedals #guitar #pedalboard #guitareffects  #guitargear #guitarist #knowyourtone #guitarpedal #stompbox #guitarplayer #geartalk #fxpedals #guitars #electricguitar #pedalboards #guitare #guitarra #chitarra
© 1963 EFFECTRODE THERMIONIC