Real McTube II Preamp.

I came across this musical instrument overdrive / distortion tube preamp while surfing around the web and thought it would be fun and inexpensive to build.

I didn't exactly build a practical version of the preamp but I bought enough parts to build a second unit.

The preamp was designed by Fred Nachbaur and can be found at Fred's Projects web site.

Fred has much more complex tube amplifiers that he has designed and created shown on his web site.

Back of Real McTube II Preamp.

The main component of this preamp is the 12AX7A vacuum tube but other tubes can be substituted for a different sound.

This preamp enclosure is really sharp looking and is a Hammond Manufacturing model 1456CE2WHBU.

The back of the preamp has a DIN connector for the filament and plate input voltages from the power supply. The audio output jack is also located on the back of the preamp.

Inside view of Real McTube II Preamp.

Arranging and soldering parts onto tube socket solder lugs and terminal strip solder lugs has quite a different feel to it than populating a circuit board.

On the shielded cables I soldered ground wires to the braided wire shields and used heat shrink wrap giving them a nice finished look.

Real McTube II Preamp and Power Supply.

I built the power supply for the preamp in a separate enclosure and the outputs from the power supply are filtered dc.

The filament voltage is regulated and measures 12.8 volts at the preamp DIN connector. The vacuum tube plate voltage measures 152 volts at the preamp DIN connector. I divided the power supply filter capacitors between the preamp and power supply.

Inside view of Real McTube Preamp power supply.

I removed the two transformers from wall worts and wired them secondary to secondary to supply line isolated high voltage for the preamp.

I also added a safety interlock using a small relay to the power supply to shut down the high voltage if the power supply output cable is disconnected from the preamp.