Poddwatt: Class-A Stereo Push-Pull EL84 (6BQ5) Vacuum Tube Amplifier

Posted on Feb 6, 2014

This project is related to the other tube amplifier projects I have posted. It has more than a casual similarity to the first Push-Pull EL84 (6BQ5) Oddwatt project from nearly two years ago. Both tube amplifier projects use EL84 / 6BQ5 tubes and the earlier one used a ECC802S driver while this one uses 5751 driver tubes. The basic circuits are rat

Poddwatt: Class-A Stereo Push-Pull EL84 (6BQ5) Vacuum Tube Amplifier
Click here to download the full size of the above Circuit.

her similar, but the new project has a number of differences. Most notably it is easier and less costly to build. The rather large output transformers used in the original project have been replaced by ones that are considerably less weighty and less costly. This alone makes for a $40 to $50 savings. A number of circuit refinements have been included as well. One area of particular note is the higher gain of this new tube amp. This was done to allow the direct connection (via headphone jack) of MP3 players to the tube amp. The earlier project with the ECC802S driver tube did not have sufficient gain for this. The end result is a great DIY project for those of you who need 5 to 7 watts of high quality sound. The amplifier is quite clean from 25 Hz to past 20kHz (see the measurements in Tables 1 and 2 below). There is plenty of bottom end, just not as much as the bigger amplifiers like the KT88 Odd Blocks which use much larger audio output transformers. I was very surprised how well this amplifier sounds. If you don`t exceed the power limits it will provide sound quality that is easy to listen to with great detail and clarity. Warning: This project uses high voltages. Contact with such voltages can cause injury or death. If you are not familiar with high voltages and how to safely build high voltage equipment, then please do not attempt this project. I want everyone to enjoy music and not have anyone harmed in the process....

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