Lamington Cake Tin Guitar Amplifier

Here's a low-cost vacuum tube guitar amplifier designed by Grant Wills of Valve Heaven in Sydney Australia. Valve Heaven offers professional guitar amp repair and restoration of all types of amplifiers, specializing in the repair of valve amps. Grant designed the Lamington Cake Tin Guitar Amplifier for the person who has basic soldering skills and a healthy respect for high voltages who wants to build a basic 15 watt valve amp head for minimal cost and with a minimum of metalworking. It was designed to use readily available “off the shelf” components, without access to a workshop or specialized tools and at low cost. Depending on how adept you are at scrounging certain components, the cost to build this amp will be around $200.

As for the name, to save cost on the metal chassis Grant designed the amp to be built on a cake tin typically used for an Australian favorite, the Lamington.

Lamingtons are a quintessential part of every Australian's childhood and a bakery delight enjoyed as a dessert or served with morning or afternoon tea. A Lamington is a piece of light sponge cake dipped in chocolate icing and rolled in desiccated coconut, as shown at right. Grant used a readily available, low cost lamington cake tin from K-Mart (but any similar cake tin will do). An inverted cake tin provides an attractive, teflon coated chassis which is ideal for the amp.

The amp design is a fairly conventional push-pull design with an output stage of two tubes doing the "pushing" and "pulling." This stage is preceded by a triode phase splitter to create the two out-of-phase signals to drive the output tubes. The preamplifier has three stages of gain from 12AX7 triodes, which include the Drive, Bass, Treble and Master Volume controls. The design is compatible with a broad range of output tubes being suitable including 6BQ5/EL84, 6V6, 6GW8/ECL86, 14GW8/PCL86, 16A5, 6CW5, 6BW6, 6CH6 or pretty much any power tube with a maximum anode dissipation of around 10 watts.

The unconventional part of this design is the power supply. To save the cost of purchasing a high voltage transformer, the design uses two inexpensive 30 volt transformers with their outputs in series to generate 60 volts AC. This is then fed into a voltage quadrupler circuit that uses diodes and capacitors to generate the 300 volts DC required.

Visit Valve Heaven for the Main Circuit schematic, the Power Supply schematic, parts list and complete instructions for creating a kit and building this amplifier.

Here's a video showing the completed kit and demonstrating it in action: