Application notes for Nutube

Advantages

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Low power consumption - Only 12mW per each channel
Low voltage Operating from 5V
High quality - Made in Japan

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STRUCTURE

Direct-heating twin triode

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Electrical characteristics

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Nutube delivers excellent linearity, close to that of an ideal twin triode.

Dimensions

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Pin assignments & hole sizes

Pin assignments

F1 : Filament 1(Left)

F2 : Filament 2(Center)

F3 : Filament 3(Right)

NP : No PinA2

GND : Internal shield, connect to GND

G1 : Grid 1

G2 : Grid 2

A1 : Anode 1

A2 : Anode 2

PCB hole arrangements. φ=1.0mm recommended.

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Basic circuit of Nutube

Example of a single amplifier

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Audio characteristics(1)

VCC=12V

Anode load=330kΩ

Measurement circuit

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Audio characteristics(2)

Frequency responses

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THD+N

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Power supply / Anode load

Power supply voltage(VCC) :5 – 80V

Please note: power supply exceeding the permitted limits will void any warranty.

Recommended anode load resistances : 100k – 330kΩ

出力インピーダンス高くなるため、後段にバッファを置くことを推奨。

Audio characteristics on each VCC voltage

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Audio characteristics
on each anode load resistance(VCC=12V)

Biasing voltage / resistance

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Grid biasing:2 – 3V(VCC=12V)

Use of trim pot is recommended for precise adjustment the of biasing voltage.

Biasing resistance:10k – 33kΩ

Considerable grid current will not allow large biasing resistance. Grid current is around 30μA at maximum.

Filament ratings

0.7V直接点灯

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抵抗によるドロップ

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Filament rating:0.7V 17mA(41Ω)

Direct current is recommended.
Inserting capacitor(10μF or more) between filament and GND improves residual noise.

Recommended resistance values connecting to filament on each VCC voltage.

各電源電圧での推奨抵抗値

Using both cirucuits

Parallel connection

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Series connection

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Parallel connection of filaments enables to have each filament to have the same voltage.

In series connection, the filament current is half of that of parallel connection, which would improves battery life.

Warning

  • DO NOT exceed filament rating (0.7V 17mA).

  • Excess filament voltage will easily burn out the filament!

  • A red-heated filament shows excess voltage.

Normal state Filament 0.7V 17mA

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Exceeded filament current(25mA)

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To prevent microphonic noise

A Nutube is a direct-heating tube which means it can cause microphonic noise.
External vibration reaches the tube mainly through the mounted circuit board and also via the air around the tube.

1.To prevent any vibration from the circuit board (Fig.1)
insert some cushioning(a sponge or something equivalent and soft) between Nutube(or the board mounting Nutube) and the main circuit board. The harness connecting Nutube and the main circuit board should be soft and thin enough.

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Fig.1

2.Prevent any vibration from the air (Fig.2)
The vibration of the air (sound) reaching the surface glass of Nutube can cause the microphonic noise especially high frequencies (a metallic sound) .

 

Placing Nutube in a protective box/case helps prevent such vibrations.
Using acoustic material in the chassis further reduces the noise.
Placing a heavy metal plate (e.g. lead) on the surface of a Nutube can also reduce noise.

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Fig.2

Nutube Differential Amplifier Diagram

The following diagram shows an example of a Differential Amplifier Circuit that uses Nutube.

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・Power supply:±12V
・Output Impedance:For a circuit receiving several hundred kohms we recommend an Impedance of 1M or more.
・Amplification rate:x1.75*By making AR1/2 bigger you can also increase the amplification rate
When using 47k the amplification rate is approximately 1
*The output level will take 1-2 minutes to stabilize
*This circuit example could also be used with any standard Vacuum Tube
*Patent pending

Output waveform

Orange: OUT1
Green: OUT2

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Input = 2 Vpp

Output = 3.2 Vpp (Amplification of x1.75)

Nutube Cathode Follower

The following diagram shows an example of a Differential Amplifier Circuit that uses Nutube.

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・Power supply: ±12V

・Internal Output Impedance 10k ohm

・Amplification rate: x0.89 (Logic diagram below)

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・OUT1 Maximum output voltage
=12.4Vpp (no load, Max input 13.9Vpp)
=1.5Vpp (Load=10k, Max input 3.4Vpp)
=3.5Vpp (Load=15k, Max input 6.6Vpp)
=5Vpp (Load=22k, Max input 8.2Vpp)
=7Vpp (Load=33k, Max input 10.2Vpp)
=9Vpp (Load=47k, Max input 12.3Vpp)

 

*To increase the output current (to use it for headphones for example), you can add a transistor and use OUT2 for output
*The output level will take 1-2 minutes to stabilize
*This circuit example could also be used with any standard Vacuum Tube
*Patent pending