Single Ended Class A 6V6 6J5 Valve (Vacuum Tube) Amplifier Circuit

This is my first successful vacuum tube project.  The output of this small amplifier in which a 6V6GT output pentode is connected as triode is about 4.5 watts.

This project involves a single ended audio amplifier, which consists of a resistive input network, a driver stage, and an output stage to a typical 8 ohm loudspeaker load, all the while, using a minimum of supportive passive components for biasing and coupling duties. Power-supply voltage is provided by  full wave diode rectification of 230 VAC by a magnetic transformer. This design provides a quality audio amplifier.

Valve amplifier circuit diagram

The major factor involving the design of this single ended output stage is matching an available output tube to an available output transformer (OT) , which can provide the proper impedance matching. Using typical operating parameters, the 6V6 power tube, operating in triode mode, has an ideal load impedance of 5k Ohm, and generates about 4.5 watts of power. An OT was used, handling 8 watts and providing impedance matching from a 5k primary to an 8 ohm secondary, which is a common loudspeaker impedance.

Tube amplifier power supply

The amplifier uses a simple linear power supply to develop 300VDC. Heater voltages are supplied directly from the 6.3VAC taps on the secondary of the power transformer. The other secondary windings, rated at 230VAC are used for the DC supply. It consists of a 4 rectifiers, variety of smoothing capacitors and resistor.

Tube Datasheets

6J5 Datasheet

6V6 Datasheet

Several construction issues were considered in the building of this amplifier. High power supply voltages, large and leaky inductive components, and high temperatures are among these considerations. I used old tube amplifier chassis.

Magnetic flux is expelled from the transformers as shown by the red arrows above. By placing the output transformer (OT) and power transformer (PT) at opposite ends of the chassis, and rotating their axes 90° from one another, induction noise from PT to OT is reduced. Although this configuration sees flux from the OT directed at the 6V6, OT flux interference into the sensitive preamp stage tube is avoided. Beneath the chassis hum reduction is further achieved by winding all pairs of wire containing AC (filament heater wires, PT primary, and secondary wiring to the diode rectifier).

6V6 Tube amplifier Video

Due to the 300V power supply voltages used, components were carefully chosen to withstand peak conditions.

Connect amplifier ground and power supply ground to the chassis ground point.

Don’t touch any component when the tube amplifier connected to the power, because it used high voltage.

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Discrete Class AB Transistor Audio Power Amplifier Circuit Diagram

This is a class AB transistor power amplifier. It is a simple amplifier to build, uses standard parts and is stable and reliable.  The entire circuit utilizes commonly available components and may be simply built over a general-purpose board. But this amplifier has very good sound quality.

There are eleven transistors, including four in the output stage. Q1 and Q2 transistor must be between 3 and 5  amperes power transistors. Q4 and Q5 must be between 100mA and 500mA driver transistors. Other transistors are 10mA small driver transistors. Q1, Q4 and Q2, Q5 are complementary pairs, they make complementary darlington pairs.

Power output of the amplifier

10W is much enough for the day today home usage.

Amplification of this amplifier (A)

Volume control can be added to the circuit by connecting a 10KΩ  POT in series to the input of the amplifier.

Q1 and Q2 must be kept sufficiently cool, so it is mounted on a suitable heat sink. If you used single heat sink please use insulation between transistors and heat sink.

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TransistorAmp BJT Transistor Amplifier Circuits Designer Software

For the design of transistor amplifiers there is a new software available: TransistorAmp. With TransistorAmp you are able to create your individual transistor amplifier with a few mouse clicks. TransistorAmp is freeware.

The tool TransistorAmp has a very easy to use user interface. You start every design with the menu item “New Amplifier”. In the pull-down-menu you choose your desired circuit. You can choose between,

• common-base-circuit
• common-emitter-circuit
• common-collector-circuit

After that you get a dialog, where you have to put in all parameters of your amplifier.

For the selection of the transistor type you can click on the button “Select transistor type from list”, and you will see a list of all supported transistor types. TransistorAmp supports some thousand transistor types. Select your desired transistor type there and click on OK. The selected transistor type will then be displayed in the dialog.

When you have completed your input in the dialog, you click on OK and see the result. You see a window with your input data, the circuit, the component values and the most important parameters of the operation point. If you want to change your design, you only need to click again on “New Amplifier” and the circuit in the pull-down-menu. The input data, which have given will be restored to the input dialog, and you can change one or more parameters.

When you are satisfied with the result, you can click on “Result – Save”. TransistorAmp saves all data which is displayed in the result window to a HTML-file. You can open this file with a browser (e.g. Firefox or Internet Explorer), inspect it and print it.

Download

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Automatic Gain Control PreAmplifier Circuit Diagram

The preamp circuit uses an easily obtained 741 op amp set for an internal gain about 200.

A portion of the op amp’s output signal is rectified by the 1N4148 diodes, then filtered and fed to the gate of the FET input shunting circuit. As the output rises, more and more input shunting takes place. That is, more of the input signal is bypassed, effectively keeping the output level constant.

BF245

This preamp circuit offers a 100:1 limiting action. The input level can change over a 100:1 ratio with little or no effect on the output level.

741 PIN CONFIGURATION

The output output level itself can be set from less than unity all the way up to nearly the gain of the amplifier, making the circuit usable in other applications as well.

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TDA2004 Car Battery 12W Stereo Amplifier Circuit

Its main features are :
Low distortion.
Low noise.
High reliability of the chip and of the package with additional safety during operation thanks to protections against :

• OUTPUT AC SHORT CIRCUIT TO GROUND
• VERY INDUCTIVE LOADS
• OVERRATING CHIP TEMPERATURE
• LOAD DUMP VOLTAGE SURGE
• FORTUITOUS OPEN GROUND

Space and cost saving : very low number of external components,very simple mounting system with no electrical isolation between the package and the heatsink.

The TDA2004A is a class B dual audio power amplifier in MULTIWATT package specifically designed for car radio applications.

With the component values shown and with a supply voltage of 14.4V (a fully charged car battery), the stereo amplifier is capable of delivering a power output of at least 6W, typically 6.5W with a load impedance of 4Ω. It can also handle a load impedance of 2Ω, in which case the output power is a minimum of 9W, but typically 10W. Power outputs of this order are subject to about 10% distortion, however, if lower power outputs are acceptable, 4W with a load impedance 4Ω or 6W with a load impedance of 2Ω, distortion is only in the order of 0.3%.

The voltage gain of the left-hand channel is determined by the ratio of R3 to R5, and that of the right-hand channel by the ratio of R4 to R6. With the values given, this will be 50dB. Therefore, a signal of 50mV is required at the input to give the maximum output. If this input sensitivity is too great, a 50kΩ stereo potentiometer can be included at the input. The impedance of non-inverting amplifier input is minimally 100kΩ.

The network consisting of resistor R1 and capacitor C5 (and R2, C6) is included to prevent the amplifier oscillating at high input frequencies. The bandwidth of the circuit is more than adequate for use as a car radio amplifier. The frequency response of amplifier is 40Hz to 16kHz (3dB points).

The IC must be kept sufficiently cool. The thermal resistance of the heatsink should be at least 4°C/W.

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Voltage Controlled Volume circuit

his volume control circuit offers an unusual approach to the well-known problem of distortion in active-device attenuators. The zero-output in this case is obtained by allowing equal signals of opposite phase to cancel each other.

The input transistor operates as a ‘concertina’ phase-splitter, producing equal-amplitude opposite-phase voltages at its collector and emitter. The two signals can be brought into complete cancellation, at the summing point, by means of preset p1. The harmonic content of the two signals is very small, but not quite identical.

There will therefore actually be an even smaller distortion output at the nominally ‘zero’ point.

If something now happens to the amplitude ratio of the signals at the summing point, there will be output passed to the buffer-stage. The necessary unbalance is achieved by means of the JFET and capacitor C2. The gate bias on the FET is set by the DC control voltage applied to point A. With this voltage close to zero the FET will be cut off, so that the above mentioned cancellation takes place. As this voltage is increased there will come a point at which the channel starts to ‘bleed off’ AC collector current from the splitter; this will upset the  balance and so cause an output signal to appear. The more conductive the FET, The more output. Unfortunately, the more channel current there flows the lower will be negative gate bias and so the greater will be the distortion of the ‘regulated’ summing component.

The trick is now to employ only a moderate degree of unbalance – so that the FET operates at low distortion percentages. The process is helped also by the always present ‘clean’ summing component. The buffer stage provides gain, so that a sufficient output level is obtained. The Circuit’s frequency response extends from 50Hz to 35kHz (-3dB points). The input voltage should be limited to 100mV p-p: the output can be varied from ’0′ to 1V p-p (by using the appropriate range for the control voltage at A).

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The LM386 is a power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but the addition of an external resistor and capacitor between pins 1 and 8 will increase the gain to any value from 20 to 200. The inputs are ground referenced while the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 volt supply, making the LM386 ideal for battery operation.

Features

• Battery operation
• Minimum external parts
• Wide supply voltage range: 4V–12V or 5V–18V
• Low quiescent current drain: 4mA
• Voltage gains from 20 to 200
• Ground referenced input
• Self-centering output quiescent voltage
• Low distortion: 0.2% (AV = 20, VS = 6V, RL = 8W, PO =
• 125mW, f = 1kHz)
• Available in 8 pin MSOP package

This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a minimum gain of 20, leave out the 10 uF capacitor connected from pin 1 to pin 8. Gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor.(when adding 1.2kΩ resistor series with C3 capacitor, gain reduce to 50. )

LM386 IC

A small electrolytic or tantalum  cap of a few uF from pin 7 to ground will isolate the high gain input stage  of the LM386 from power supply noise, hum, transients, etc.Such a bypass  cap is much more effective in this case. Most commercial rigs (and kits) using the LM386 either fail to bypass pin 7 at all or use too small a value  (0.01uF or 0.1uF) to be totally effective and increasing the value to 4.7uF  completely eliminates the “thumps” in the audio output produced by Vcc  transients when the transmitter is keyed.

LM386 Connection Diagrams

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FM Booster, Active FM Antenna Amplifier

This FM booster that can be used to listen to programmes from distant FM stations clearly. The circuit comprises a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570. (Only C2570 is annotated on the transistor body.)

Assemble the circuit on a good-quality PCB (preferably, glass-epoxy).

Adjust input/ output trimmers (VC1/VC2) for maximum gain.

Input coil L1 consists of four turns of 20SWG enamelled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns.

Pin configuration of transistor 2SC2570

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6 Band Graphic Equaliser Using 741 Op-Amp IC

With this circuit you can control and blend frequencies and tones as desired.

Essentially, the circuit consists of an IC 741 whose gain at various freguencies is determined by corresponding potentiometer setting.

The audiblefrequency spectrum is covered in six steps: 50Hz, 160Hz, 500Hz, 1.6kHz, 5kHz, 16kHz. All potentiometers are of 100kΩ linear type. The circuit provides adequate boost / cut for normal use.

power supply for the circuit can be derived from the amplifier / preamplifier itself. The wide rangeof supply voltage (6V-15V) makes the circuit very versatile. Power consumption is negligible.

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HeadPhone Amplifier OR PreAmplifier OutPut Stage

This 1 watt amplifier lends itself par excellence for use as driver for low impedance headphone or as output stage in a HI-FI preamplifier driving an active loudspeaker. Many preamplifiers do not permit long, unscreened leads to be connected to them, but the present amplifier accepts these happily.

This circuit consists of an OpAmp type LF356 and a push-pull transistor output stage. Low-pass filter R1/C2 at the input limits the slew rate of the input signal. In conjuction with the relatively fast LF356, this results in very low delay distortion. The fixed quiescent current of 30mA drawn by the output transistors, and set by diodes D1 … D4 in conjunction with emitter resistors R7 and R8, ensures very low crossover distortion.

Feedback resistors R3 and R4 fix the gain at about 15dB. The consequent overall distortion with a 3 dB bandwidth from 10Hz to 30kHz is only 0.1 per cent.

LF356

The amplifier delivers a maximum power of 1 watt into 8Ω for an input signal of about 500mV _rms. High-impedance headphones and 4Ω loudspeakers may also be connected with detriment.

To enable it surviving a shot circuit at the output, the two transistors should be mounted on heat sinks, do not forget the insulating washers and the conducting paste.

The power supply need not be more than a simple affair, consisting of a mains transformer with a centre-tapped, 6…8V, 0.5A secondary, a suitable bridge rectifier, and two 1000µF/16V electrolytic capacitors in a conventional arrangement.

To drive high-impedance headphones at high volume, you need a ±15V regulated power supply: in some cases, this may be derived from the preamplifier supply, IN this arrengement, care must be taken not to short-circuit the output terminals.

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