The Lummerland Express is loosely based on Ken Fisher's Trainwreck, except that the power section is not driven by EL84s, but rather a dual triode, usually found in preamps.
In addition to a 12AU7, the Lummerland Express also works without problem with a 12BH7 or ECC99 - while the 12AU7 or 12BH7 will produce about 1.5 watts, the ECC99 will produce about 3.5 watts. This doesn't sound like much, but it is, and is often underestimated. For example, the effiency of most guitar and bass loudspeakers is measured at a distance of 1 meter with a power input of 1 watt, and they produce a sound pressure level of 97 or 98 dB, or even more. In no sense of the word is this "quiet."
The advantage of low-watt amps is that they can be turned up to '11' without immediate and permanent ear damage. Just try that with a 100W Plexi ...
As mentioned, the circuit (especially the preamp) is clearly a copy of the Trainwreck circuit, with slight modifications. The mid control has been replaced with a fixed resitor. Other modifications of the tone stack were necessary to reduce the bass response a bit, as the Lummerland has more than enough bass. Other modifications were necessary to work with the power stage.
The output transformer is a Hammond 125B set up for an Raa of 22k, which works well with a 12AU7, 12BH7, and ECC99, although with a slight but unimportant impedence mismatch for each tube.
Unlike the Firefly, which uses a self-split power stage, the Lummerland drives the output tubes with a cathodyne phase
inverter. The concept is completed with a master volume, which permits overdriving the preamp at low volumes. The Trainwreck acolytes may be disturbed by this, as the original has no master, but if it is not wanted, it can be easily omitted.
If you are searching for the power supply on the schematic, you will not find it - we use the standard power supply module from the shop, which provides more than enough voltage and current and requires minimal real estate. There is no need to re-invent the wheel.
The voltage connections B2 and B3 in the schematic refer to the outputs of the power supply.
For the chassis, we have developed a special design just for this type of amp - unless, of course, you prefer to do your own metal work. The components are also standard. Construction is point-to-point, with the components on a sort of mini-board which is also used in the LoV projects. The board is big enough so the components fit in an orderly way, but small enough, so that in the end the amplifier is very compact.
Finally, the mother of all amp questions: how does the Lummerland Express sound? Answer: very good ;-)
Tone is difficult to describe, subjective, and affected by countless factors, so that it is difficult to put into words. The Lummerland Express is not a Bassman clean ultralinear amp. That isn't the goal of the amp, and it will will not satisfy you if that is your goal. Although it reacts well to the guitar's volume pot, and can be set to play relatively clean, there is always a certain amount of distortion. The Lummerland shines when the gain control is hard clockwise, the master not far behind, and the guitar has fat humbuckers. Full sound from rock through 80s meta, but not a modern heavy metal sound. The sound
is tight and the bass clear. The tone is full, and the bass pot will be more often under 12:00 than over, depending on the guitar and speaker. All in all, a real (low-power) rocker.
For some people, the Lummerland sounds too smooth and somewhat undefined at the low end. As a remedy just replace these components / values:
R6: 6,8 kOhm
C5: 1 nF
Soundsample 1 @ YouTube
Soundsample 2 @ YouTube
Care is necessary during construction! Even though this is a low-watt amp, the voltages used are potentially fatal. The Lummerland 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.