AV 520B SLX Datasheet


Nearest Replacement:

EML1605 (5Volt Heater)


The AV 520B SLX is a  high power tube, with flat graphite flat Plates.  The graphite will not suffer from deformation when the tube is run at full power.  The hard metal filaments can  not break.  This  tube can be used at full power,  without any need for derating, and keeping the full guarantee. This tube shows at its best the capabilities of AVVTs unique hard-metal cathode wire. 


  • This tube uses AVVT's unique Super-Linear Patent (Note1) 
  • AVVT's patented ribbon filaments with 16 flat Surfaces, for more linearity 
  • Four extra large getters
  • Solid Graphite Plates, with Super Linear cavities. 
  • Pyrex II high temparature Glass 
  • Anti-microphonic Suspension in Tube Top 
  • All 1999 (and later) AVVT tubes use unbreakable hard-metal filaments. (Note2
  • Ceramic UX4 Socket with Gold Plated pins 

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AV 520B SLX Filament Ratings
Filament Voltage 
6 Volt (AC or DC) 
Filament Current 
2.5 Ampere 

AV 520B SLX Maximum Conditions (See also Note 3)
Plate Voltage 
Plate Current 
Plate Dissipation 
Power Output in Class A 

AV 520B SLX Typical Data 
Plate Voltage 
Plate Dissipation 
75 Watt 
Plate Current 
Grid Voltage 
Plate Impedance 
550 Ohm 
Amplification Factor 
6.5 mA/V 
Load Impedance 
1500 - 3500 Ohm 
Operating Lifetime 
40.000 hours 
Grid resistor
47k Ohm

AV 520B SLX Mechanical Data
Size (Including Socket)
200 x 65mm  or  7.8" x 2,55"
190 Grams 

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Note 1)  Super Linear Anodes are based on an exclusive AVVT patent.  The cold ends of the filaments do not have a very good function, and cause distortion.  This tube has  four cavities inside the anode, that cover the cold ends of the filaments. These cavities are covered by four nickel plates, that you can see from the outside.  Within these cavities, anode current will not be able to flow,  and this disables the emission of the cold end of the filaments. 
Note 2)  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 3  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 has  is numbered, inside the bulb  with a metal Tag

Tube pictures with courtesy of VT-Components

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