Yet another Hiwatt - the name says it all. Consistently developed for maximum headroom, which can only be achieved by a high wattage.

The YAH100 kit is based on a Hiwatt DR103 from the early 70s, which delivers 100 tube watts from 4 EL34 and is quite common. On the input side there is one Hi/Lo input pair in the "Normal" channel and one in the "Brilliant" channel, which can be individually controlled in the volume. Both channels are ending in the same 3-band tonestack after the first gain-stag. From there it goes to another amplifier stage and then via a cathode follower to the phase inverter which powers output stage. Everything is rounded off by a master and a presence control.

The circuit was almost completely implemented according to original specifications. Only for the bias-supply we decided to use an adjustable solution. This allows a better adaptation of the tubes to the amplifier and also offers the possibility to try something different from EL34 - for example KT77 or 6CA7 - without having to change the circuitry.

Everything is built up on a turret board, but some components are also soldered directly to other components, such as capacitors or potentiometers. Just like real point-2-point.

In order to build the amplifier successfully and get it running, you should use a reasonable soldering iron to warm up the turrets properly and to achieve a stable connection between the turret, the wires and other components. The use of high quality solder should also not be forgotten, as well as a fair assessment of your personal skills and knowledge in amplifier construction. The construction of the amp looks quite manageable, but is by no means a beginner's project or an activity that can be done "on the fly". This is the only way to ensure that you will have fun and pleasure with your amplifier for a long time and that it will work reliably.

We recommend to use the Sovtek 12AX7LPS on the V1 position. For the remaining positions the JJ 12AX7, as well as standard EL34. Since the bias can be adjusted, the EL34 need not have a certain grade, but should be matched in a quartet. With the recommended bias setting the amplifier delivers up to about 105 watts when running at full power.

Schematic and Layout

Schematic (PDF, 3 Pages)

Layout 4 Pages (PDF, ca. 8 MB)


You can find lots of information about Hiwatt amplifiers on hiwatt.org

Warning !

Care is necessary during construction! The voltages used in this amp are potentially fatal. This amp is NOT a beginner's project!
A successful build requires that you can read (and understand!) a schematic diagram, you know how to use various measuring devices, and you have some experience working with voltages over 60V.


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