This is old schematic of Tube Phono Pre-Amp – 12AT7. Because The 12AT7 is not the most commonly used preamp tube in audio. That distinction probably falls to the 12AX7.

12at7-phono-preamp

Manufacturer :
Type : Tube Phono Preamp
Number Of Tubes : 2/1
Tube Type : 12at7
Voltage : 120V
High Resolution Scan : Available
Some notes about this schematic : None

To download high resolution schematic you can fill your email in the comments form of the schematic.

This tube is equivalent with : 12AT7 / ECC81 / CV4024 / CV455 / A2900 / B739 / ECC801S

Material :

Resistor:
250K
20K
100K 3
10M 2
10K 2
3 Ohm

Capacitor
0.001uF 2
0.02uF 2
0.05uF
20uF/ 200V 3

Tube 12AT7 (mono)

VR100 Ohm

Dioda for 120V, 20mA

Trafo
Primary
AC100V / 220V

Secondary

6.3V / 0.6A
120V 20mA

12AT7 Tube Detail

12AT7 (also known in Europe by the Mullard–Philips tube designation of ECC81) is a miniature 9-pin medium-gain (60) dual-triode vacuum tube popular in guitar amplifiers.

It belongs to a large family of dual triode vacuum tubes which share the same pinout (EIA 9A), including in particular the very commonly used low-mu 12AU7 and high-mu 12AX7.

So this tube has somewhat lower voltage gain than the 12AX7, but higher transconductance and plate current, which makes it suitable for high frequency applications.

It also found wide use in audio as a driver and phase-inverter in vacuum tube push–pull amplifier circuits. And this tube is essentially two 6AB4s or two EC92s in a single envelope.

The tube has a center – tapped filament. So Either 6.3V 300mA or 12.6V 150mA heater can be use in this tube.

The 12AT7 is a miniature, high-mu twin triode designed for use as a grounded-grid radio-frequency amplifier or as a combined oscillator and mixer at frequencies below approx 300MHz. This tube has a mu factor of 60, as compared to the higher gain 12AX7 with a factor of 100, and the 12AU7, with a mu of only 20.

As each triode section in normal use operates many high fidelity applications as a class A amplifier tubes. They also turn up in line and microphone preamplifiers, musical instrument amps, and vacuum tube equipped recording equipment. By their design, they are inherently low noise, making them a good choice for these applications. A noval nine-contact socket for this tube and can mounted in any position.

Source : Wikipedia

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