AV 20B / AV 20M  Datasheet


AVVT 20M replace by: EML20A-Mesh
AVVT 20B replace by: EML20B


The AV 20B / AV20M  is  a very universal  and stabile tube, combining high gain, with a low output impedance. At a gain of 20,  at only 11 Watt dissipation, there is no comparable directly heated tube, that offers a  plate impedance of 3200 Ohm. 

As a driver tube,  when using a plate resistor, it can work with high voltage circuits is typically used for an 845, 211, or VV520B, using a supply voltage of  500...1200 Volts.   For lower Supply voltages the use of a plate choke is recommended.   With a plate choke the tube can run  at Supply  voltages of 350...450 Volt.   (See Note4 for use with HV tubes) 

As a lower signal tube, you can work at any required lower voltage, since you don't need to generate a maximum voltage swing. 

As an output tube, use  450 Volt supply voltage for obtaining the maximum output power of 2.5 Watt. 


  • AVVT's parallel ribbon filaments with 16 flat Surfaces, for more linearity
  • Two extra large getters
  • White  nickel plates
  • Unbreakable Hard-Glass Bulb, or thin  C37 Shaped Glass
  • Anti-microphonic Suspension in Tube Top
  • Hard-metal filaments, which can never break. ( Note1)
  • Ceramic UX4 Socket with Gold Plated pins

AV 20B, white  nickel plates
Click to enlarge Picture
Click here for a Side view

AVVT20B plate curves.


Filament Ratings 
Filament Voltage 
5 Volt (AC or DC)
AC only as Output Tube
Filament Current 
1.3 Ampere
Maximum Conditions     See  Note2
Plate Voltage 
Plate Current 
Plate Dissipation 
Power Output in Class A 
Typical Data 
Plate Voltage 
Plate Dissipation 
11 Watt 
Plate Current 
Grid Voltage 
Plate Impedance 
3200 Ohm 
Grid-Filament capacitance
Amplification Factor 
5,3 mA/V 
Grid Resistor
100k Ohm
Operating Lifetime 
40.000 hours 
Bias suggestions  (with Plate Choke) 
    Ua   /   Ia     /    Ug 
Uin-max  / Gain / Load
  See  Note3
  350V / 32mA / -10V           7,1V  / 16,0  / 100k
  400V / 40mA / -11V           7,8V  / 15,9  / 100k 
  450V / 35mA / -15V         12,0V / 15,8  / 100k
Bias suggestions  (with  Plate Resistor) 
  Ua   /   Ia    /   Ug   / Ra  /  Ub
Uin  / Gain / Load
  See  Note3
325V / 24mA / -10V / 12k /  600V 
  7,1V  / 13,1  / 100k
350V / 21mA / -13V / 22k /  800V 
  7,1V  / 14,4  / 100k
375V / 18mA / -15V / 35k / 1000V 
 7,8V  / 15,0  / 100k
400V / 16mA / -17V / 50k / 1200V 
10,0V / 15,5  / 100k
Mechanical Data 
Tube Size including Socket: 170 x 60mm
Tube Weight 
130 Grams

For further information about our products, please visit

Note 1) Hard-metal filaments are operated at much higher temperature than normal tubes. This tube will glow bright orange, instead of the dark orange color of nickel filament tubes. 
Note 2) Individual Test data, such as: Matching Data, Grid Current, Vacuum, Filament Current, etc, are on the Certificate that comes with each individual Tube. Each tube  is numbered, inside the glass with a metal Tag
Note3)  These are just suggestions.  Other bias points can be constructed using the tube curves. Va=DC Plate Voltage,   Ia=DC Plate Current,  Vg=DC Grid Voltage, Vb= Power Supply voltage. Vin=Maximum effective  AC input voltage, Gain=Amplification Factor,  Load=The Input Impedance of next stage. 
Note4)  When the operating voltage of an 845 circuit is for instance 1100Volt,  choose a plate resistor for the 20B / 20M that will give the  operating points as in the table " Bias suggestions with Plate  Resistor"   The voltage over the plate resistor will be 700...750Volt. Do not use one single resistor, because the types with cooling mounting, or any other type that is sand filled, will produce pop noise, that you think may come from the tube.  For the plate resistor you will get best results with metal film resistors of maxium 5Watt in Series,  to obtain the required value. At 1200 Volt Vb, you will need five of these.   When switching on the HV, you MUST pre-heat the filaments first.  Otherwise you are limited to 450Volt supply voltage. 

Tube pictures with courtesy of VT-Components

Counter since 18.12.99 
JAC-MUSIC  ©2001. All Rights Reserved.