The original idea for the „HotLukas“ was to expand the Matchless "HotBox" with a small ECC99 output stage - but unfortunately the result did not meet our expectations.
However, since the topology of the Hot Box was well suited for another LoW project, a second attempt was made. The weak points of the original concept were eliminated and adapted to the already proven ECC99 output stage.
In addition to tonal adjustments the available overdrive has also been increased. This turned the “HotBox” into a “hot rodded HotBox” or simply the “HotLukas”.
In comparison with the original "HotBox" the effectiveness of the tone stack has been increased. The last triode system of the second 12AX7 was converted into a cathodyn phase inverter instead of a cathode follower, which drives a ECC99 push-pull output stage. It is also possible to use an other output tube than the ECC99, for example to reduce the output power even more, but the use of the ECC99 is warmest recommended.
The clean channel, which is available at the "HotBox", was omitted ultimately. On the one hand for reasons of available space and on the other hand because of a significant volume jump, which occurred between both channels. Adjustments would be possible of course, but we decided to integrate a boost instead of a clean channel. The boost is located between the first and second gain stage and can be controlled by a foot switch (switch, not momentary). Strictly speaking, there is no boost but a damping which in the off state of the boost drops a portion of the signal to ground, resulting in reduced overdrive. Without a foot switch connected the boost is always active. A very simple but very effective solution, especially as the volume difference between the two settings is rather small, but the difference in the resulting overdrive is high.
The sound of the "HotLukas" will appeal to friends of cultivated overdrive in the first place. The amp can be set from warm blues overdrive to hard British drive and fits perfectly with a Strat or a Tele but also with Les Pauls and SGs. Clean is not the strength of this amp, but it was clearly not the goal in the design of the amplifier. The HotLukas makes the most pleasure when it is played with full gain and a guitar with high output pickups.
Caution is necessary. Even though this isn't a particularly powerful amp, it nevertheless works with voltages with are potentially lethal. This amp is NOT appropriate for beginners!
Reading and understanding schematics, use of measurement devices, and good experience with voltages over 60V are prerequisites for the successful completion of this project.