Tempo Electric writes: “In the 1970s, influential Franco-Japanese audio designer Jean Hiraga declared the 300B to be “the tube of the century.” During his teen years in Montreal, Dr. Arthur Loesch (pronounced “Lesh,” like the Grateful Dead’s Phil Lesh) studied French and later read Hiraga’s original articles in Revue du Son, Revue L’Audiophile, and Nouvelle Revue du Son.”
“In the 1980s, calling on his background as a research scientist in physics and mathematics, Dr. Loesch developed his own Single Ended triode (SET) circuit and became a major figure in its revival for home audio in North America.
In the early 2000s, working in both Dr. Loesch’s basement “audio cave” in Guilderland, NY, and our own dedicated testing room in nearby Troy, NY, we collaborated for over a year to optimize his circuit using the most advanced components available. The result was the Series 300 Mono Amplifier. Today, the Series 300 Mono Amps are avaialble in a variety of configurations, all based on the 300B power tube, which was his favorite.
Possibilities include
- Single-Ended x (1) 300B (8 watts output)
- Single-Ended Parallel x (2) 300B’s (20 watts output)
- Push-Pull x (2) 300B’s (20 watts output)
- 2 or 3-Stages of amplification
The Sound
The Series 300 amps bring out the best in the 300B. Highs are clean and detailed; the midrange rich and vibrant; the bass solid and resonant. Sound staging is wide, deep, and three-dimensional. Overall, there’s a presentation that’s unusual in an all-tube design. These amplifiers produce music with the impact of a live performance, sailing through the most difficult recordings as they lift the last veil between you and the stage.
We spent hundreds of hours voicing the circuit using matched pairs of 1940s vintage Western Electric 300B’s as a reference, so that every internal component compliments each other and none distracts from the overall sound. Onboard iron includes ISO (formerly Tango) output transformers, custom built Heyboer power transformers, and vinatge American filter chokes.
AC vs. DC Filament Supplies
Unlike most modern tubed amps, Loesch designs feature AC on the power tubes’ filament supplies (heaters), rather than DC. Although DC on the filaments is inherently quieter, it forces the tubes to have different bias readings on each filament. This variation in the left and right filaments results in unequal plate current across the tubes and compromises their linearity. The net result is the introduction of distortion that does not exist with AC. Subjectively, AC on the filaments makes the sound more realistic.
While AC on the filaments is often criticized for amplifying the 60Hz (or 50Hz) line frequency (characterized by a faint background hum), the Series 300 amps filter out the hum by incorporating a line frequency filter just ahead of the heaters. The result is that the AC heated filaments are just as quiet as those heated by DC without DC’s inherent distortion.
Western Electric UltraPath Mod
Enriching the sound even firther, the latest version incorporated the Western Electric UltraPath modification. This was a scheme first developed in the 1930s and revisied 60 years later by the late Jack Elliano of Electra-Print Audio and circuit designer Lynn Olson.
Recomended Features include
- Pure Class A Performance
- Intact Audio by Dave Slagle Permalloy Output Transformers (Single-Ended)
- ISO (Tango) Output Transformers (Push Pull)
- Hashimoto Output Transformers (Parallel SET)
- Choke Input after the rectifier
- ASC Polypropylene in Oil filter capacitors
- Intact Audio by Dave Slagle Permalloy Interstage Transformers
- Teflon® tube sockets
- Zero Negative Feedback
- AC heated filament supplies
- Western Electric UltraPath Mod
- Secondary filter that eliminates the line hum often associated with AC filament supplies
- Teflon® insulated, pure silver wire throughout the audio signal path.
- Teflon® insulated, silver-plated copper wire throughout the power supply.
- Teflon® Tube Sockets, made in Italy
- Film capacitors throughout, including the power supply
- Caddock MS Series Power Resistors
- Furutech 15A IEC Teflon® Power Inlet
- WBT NextGen Ag Pure Silver RCA input sockets
- WBT NextGen Ag Pure Silver binding posts
- Upgrades (available at additional cost):
- Separate Filament Supplies
- Power supplies built on separate chassis
- Ladder type mono volume controls
- Recommended Premium Tube Sets:
- Emission Labs Classic or Mesh Plate 300B, Takatsuki TA-300B, Western Electric 300B
- RCA 5U4GB or Emissional Labs 5U4 (with the EML or Takatsuki 300B)
- Raytheon 6J5WGT or G.E.C. 6J5 (in the 3-Stage design)
- RCA 801A or Western Electric VT-25-A (in the 3-Stage design)
- Western Electric 417A (replaces the 37 and 6J5 in the 2-Stage design)