Analog Metric 2A3 Operating instructions

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2A3 SE Valve Amplifier Kit
User Manual
Analog Metric
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Copyright© 2012 All Rights Reserved

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SPECIFICATION
●Vacuum tubes: two 2A3 and two 6SN7 vacuum tubes.
●Voltage gain: 1.7dB
●Gain flatness: <0.9dB for 20-20kHz
●3-dB Bandwidth: 31.2kHz
●Frequency range: 20-20kHz
●Input Impedance: 87k Ohms
●Input sensitivity: 3.5V RMS
●S/N Ratio:
> 98dB (5W, 8 ohms, 1kHz)

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>110dB (5W, 8 ohms, 1kHz, a-weighted)
●THD+N < 4% @1kHz
●Maximum Output Power: 5W at 8 Ohms
●Output transformer 10-15W:
Primary impedance: 2.5k/3.5k Ohms 120mA
Secondary impedance: 4, 8 and 16 Ohms
●Stereo single-end input and output
●Power requirements: one or two 280V DC (total 300mA), 6.3V AC/DC (1.5A), and
two 2.5V AC/DC (2.5A).
●PCB dimension: 196mm (W) x 175mm (L)
●PCB thickness: 2.4mm, double layer, 2oz copper.
PRECAUTIONS
•Do not use any body parts to touch the metal parts of the kit after power up or power
off, since the high voltage capacitors may not fully discharge. It may cause serious
electric shock.
•Use a power transformer with fuse (3A) socket to limit the supply current in case of
short circuit or incorrect assembly.
•Double check the assembled components with the part list.
•Do not attempt the measure the voltage by multimeter with hand after power up. The
probes of the multimeter should be mounted by some stands to the points of the
measurement before switching on the power supply.
•Turn off the power supply if you observe any smokes or hear strange sound coming
out from the transformer or board. If there is short circuit, the transformer will be
getting very hot shortly.
PROCEDURES

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1. Solder the resistors on the top of the board. The resistance label of the Dale resistors
should face upward for easy of future debugging or modification.
2. Notice to the direction of the electrolytic capacitors C1, C3-5, C7, and C8 (the
positive terminals are marked by red circle as shown in Figure 1). There is no
direction of the thin film capacitors. Double check the direction of the electrolytic
capacitors, as it may cause hazardous.
Figure 1: The positive terminal of the electrolytic capacitors are marked by red circles.

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3. Solder the tube sockets. The bigger holes of the 4-Pin plate sockets correspond to the
PIN1 and PIN4 of 2A3 (tube filament voltage). The direction of the 8-Pin octal tube
sockets for 6SN7 match with the screen silk of the board as in Figure 2.
Figure 2: Direction of 4-Pin tube sockets for 2A3 and 8-Pin octal tubes sockets for 6SN7
4. Solder all remain components of the board.
5. Apply 6.3V DC (2A) to connector HL, two 2.5V DC (2.5A) to H1 and H2, and one or
two 260V DC (total 300mA) to P1. The tube filaments grow up gradually when turn

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on the power supply. Turn off the power supply if there is a suddenly dropping in the
supply voltage at P1, H1, and H2, or HL.
6. Adjust the cathode current Ic by the resistor trimmer VR1 and VR1B as in Figure 3.
Measure the voltage V1 and V2 across R6 and R6B, respectively, so that Ic = V1/R6
= V2/R6B is set.
Figure 3: Adjusting the cathode current by resistor trimmer VR1 and VR1B.
7. Connect the S15 SE 15W transformer with 2.5KΏor 3.5KΏprimary windings
(120mA) to the ROUT and LOUT of the board .

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TROUBLESHOOTING
VCC for B+ HL for 6SN7
H1/H2

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