This is a single stage custom made 301a directly heated(DHT) tube preamp using excellent Lundahl LL2745 output transformers. The input is direct coupled through dual Alps potentiometers. It uses two Coleman filament regulators for a very quiet preamp. According to the designer using LL2745s the gain is about 3dB with an output impedance of around 470 ohms. This works perfectly for use with most current DACs which usually tend to have a high output.
The audio tubes are select Cunningham CX-301A and are readily available as NOS or used. These tubes are from 1920-1930s and have special sound probably related to the fact that they have Thoriated Tungsten filaments. Their sockets are mounted using neoprene.
The power supply uses three transformers (one for main HT and two for the DHT filaments). The high voltage is provided by tube rectification (6BY5GA) and LCRC filtering with a 30H/40mA choke followed with two 10uF Obbligato caps parallel with 47uF Mundorf Mlytic and then followed by a solid state shunt regulator.
The wooden enclosure is made of American cherry wood with a light oil urethane clear coat protection. The inside of the case is screened using a 5 mil 99.99 pure copper foil. Top plate is brushed aluminum. Includes a manual and schematic from the builder. You can see his blog for the amp build here:
https://simplepleasuretubeamps.wordpress.com/2015/03/With my Omega Alnico single driver speakers the sound is very clear and rich with great dynamics and presence.
I will also include an extra rectifier and an extra matched pair of CX301A tubes. Other variations of the 01A tube are also available separately for some tube rolling fun.
