The circuit above is complete circuit contains tube amplifier circuit diagram and power supply circuit diagram. To make the stereo channel amplifier, build the similar amplifier circuit only and connect to the power supply using parallel connection with another same amplifier.

The tube EL34 is a thermionic valve or vacuum tube of the power pentode type. It has an international octal base (indicated by the ‘3’ in the part number) and is found mainly in the final output stages of audio amplification circuits and was designed to be suitable as a series regulator by virtue of its high permissible voltage between heater and cathode and other parameters. The American RETMA tube designation number for this tube is 6CA7. The Russian analog is 6P27S (Cyrillic: 6?27C).

The tube EL34 was widely used in higher-powered audio amplifiers of the 1960s and 1970s, such as the very popular Dynaco Stereo 70 and the Leak TL25(mono) and Stereo 60, and is also widely used in high-end guitar amplifiers because it is characterized by greater distortion (considered desirable in this application) at lower power than other octal tubes[citation needed] such as 6L6, KT88 or 6550.

20W power tube/valve amplifier circuit diagram with EL34

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Vcc – Pin 1 IC1
+12v – Pin 8 IC2, IC3, IC4
-12v – Pin 4 IC2, IC3, IC4
Ground – Pin 8 IC1

IC1 – 4049 CMOS Hex Inverting Buffer
IC2, 3, 4 – 5532 Dual Low-Noise OpAmp
D1, 2 – 1N4001
D3, 4, 5, 6, 7 – 1N4148
All 1uf caps 50v all others 25v unless
marked otherwise.
All resistors 1/4W, 5%

Channel 2 is identicle to Channel 1, and uses IC4b for the clipping meter and IC3 for the input/output driver. The input impedance of the TubeHead is about 20k ohms, which is consistant with most gear like Synths, Effects Processors, Mixers, EQs, and so on. 20k is too low for a proper match with high impedance sources like guitar pickups, but a few minor changes take care of this. To use the Tube Head as a instrument pickup preamp, remove the 47k* resistor and the 20pf capacitor from the feedback loop of the driving Op-Amp. Then change the 47k” resistor to 680k and the 22k resistor in the feedback loop of the driving OpAmp to 100k. Now the Tube Head can be used to warm up a cold sounding guitar amp or just provide a great preamp tone.

Designed/Manufactured by PAiA Electronics

Download Tube Head circuit + components list and explanation in pdf file:

Tube Head Pre-amp Circuit

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Preview:

Preamp Section:

Download the complete scheme of Orange 125MK3 Guitar Mods from the following link:

125MK3 Guitar Mods Scheme

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Schematic Diagram:

Power Supply:

Component List:

It is a classic design of power amplifier 35 W using tube, with two EL34 in connection Push-Pull, by Siemens & Halske, with design date 03/24/1953 and code SV410 / 1. The amplifier worked from 1954 to 1989, whenever and went off, with an average lifespan of 15 hours a day. Showed no particular damage beyond the replacement tubes, resistors and capacitors, resulting from natural wear.

A significant change was the replacement of the rectifier device of lamp diodes. The only problem will be for those who try their construction, will be the output transformer (applies to all tube manufactures), because the code is not helpful. Can be replaced with a conventional output transformer suitable for EL34. During the construction, it is need (applies to all circuits respectively) enough electronic experience and attention to the high voltage, electric shock risk.

source: http://users.otenet.gr/~athsam/Power_amplifier_EL34.htm

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Schematic Diagram:

Component part list:

PCB Layout:

Component Placement:

Take a note that this amplifier requires dual polarity power supply. Build the power supply using center tap transformer with output current 2A minimum and output voltage 30V, use about 6800 uF – 10000 uF electrolityc capacitors (elco). Good luck.

source: http://users.otenet.gr/~athsam/power_amplifier_35w_with_lm391.htm

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An envelope follower/filter combination translates the typical dynamic properties of your axe into modulated timbral changes too, you could feel of it as an automatic wah-wah pedal.

Independent Initial Frequency and Sensitivity knobs provide you with the control you have to notice a wide range of effects and enable the Motion Filter to be put to use with either electric bass or guitar. You will not believe that so much funk and soul can be squeezed into a tiny box.

IC1 – 4136 Quad Op-amp
IC2 – 4066 Quad Switch
D1, D2 – 1N4148 or 1N914

Circuit Notes:
Connect pads marked “A” together. Offset can be a trimmer potensiometer which could be adjusted after around a quarter-hour of “burn in” time. Fine-tune it until you hear no popping when pushing the Cancel switch S1. There is certainly no need to play into effect during adjustment. Proper setting ought to be close to the center of the rotation.

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This A/B Box effect was originally designed for switching between different harmonica mics. This A/B Box featured low noise dual preamp for better performance.

IC 5532 types (example: NE5532, NE5532A, SA5532, and SA5532A which manufactured by Texas Instruments) are high-performance operational amplifiers combining excellent DC and AC characteristics. They feature very low noise, high output-drive capability, high unity-gain and maximum-output-swing bandwidths, low distortion, high slew rate, input-protection diodes, and output short-circuit protection. These operational amplifiers are compensated internally for unity-gain operation. These devices have specified maximum limits for equivalent input noise voltage.

Download the schematic of A/B Box Switch with Dual Op-Amps:

A/B Box Switch Circuit Pedal

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This document is the manual of 2x90W Stereo Tube Power Amplifier with EL34, model K4040 by Velleman. The document in PDF version contain of schematic diagram, part list, component guide, step by step how to build the circuit. This circuit is for advance hobbysts…

Stereo Tube Power Amplifier Features:

• Pure valve sound with high quality EL34 valves.
• High quality black and chrome housing.
• Chrome valve socket covers.
• Easy bias adjustment with LED indication.
• Removable bottom for easy access and service.
• High quality capacitors and components.
• Gold plated input and speaker terminals.
• Standby function.
• Soft start circuit for power transformer.

Stereo Valve Power Amplifier Specifications:

• 2 x 90Wrms in 4 or 8W.
• Up to 2 x 15Wrms full class A.
• Bandwidth: 8Hz to 80KHz (-3dB/1W).
• Harmonic distortion: 0.1% @ 1W/1KHz.
• Signal to noise ratio: >105dB (A weighted).
• Input sensitivity: 1Vrms.
• 115VAC or 230VAC / 500VA max.

Download the complete TUTORIAL of 2x90W Stereo Tube Power Amplifier with EL34 from the following link:

Stereo Valve Power Amplifier

1 file(s) 1.32 MB

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This is a small 12W audio amplifier over a load of 8 Ω, that combining the NE5534 integrated with a pair of V-MOSFET transistor output stage technology as we get excellent sound performance. MOSFET 2SK135 / 2SJ50 from Hitachi is used in this circuit. Input sensitivity of the circuit is 3V RMS maximum, the distortion factor is 0.002% at 1 kHz, and the frequency response is 15 Hz to 100 kHz. (-3dB).

This circuit requires a symmetrical (dual polarity) power supply with voltage output +/- 25V and the current output should be 2A maximum.

12W Audio Amplifier Components List:

Power Supply Specification:
Voltage: Symmetrical 25V
Current : 1A – 2A Max

MOSFET 2SK135 and 2SJ50 Datasheet Downloads:

SK133, SK134, SK135 Datasheet

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2SJ48, 2SJ49, 2SJ50 Datasheet

1 file(s) 193.15 KB

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If you use it with only one 8 ohm speaker, it will deliver a power of 100w. The printed circuit board has the following measures: 13.6 cm x 13.9 single sided. The power supply used for this circuit is a symmetrical type which capable to delivers ± 50 VDC by 4 Amperes to the circuit. The power supply schematic is included in this board.

200W Amplifier PCB Circuit Board

200W Power Amplifier Parts

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