• Country
• Portugal

• Manufacturer / Brand
• Homebrew - RECENT but NOT Replica; Portugal

• Year
• 1994–1998 ?

• Category
• Audio Amplifier or -mixer

• Radiomuseum.org ID
• 339369

Click on the schematic thumbnail to request the schematic as a free document.

• Number of Tubes
• 7

• Valves / Tubes
• 6SN7 6SN7 6SN7 211 211 5R4GB 5R4GB

• Main principle
• Audio-Amplification; Hi-Fi-High End products

• Wave bands
• - without

• Power type and voltage
• Alternating Current supply (AC) / 230 Volt

• Loudspeaker
• - This model requires external speaker(s).

• Power out
• 13 W (undistorted)

• Material
• Metal case, TUBES VISIBLE

• from Radiomuseum.org
• Model: JM Dual Mono Class A Triode Single End Audio Amplifier 211SE - Homebrew - RECENT but NOT

• Shape
• Tablemodel, with any shape - general.

• Dimensions (WHD)
• 300 x 240 x 600 mm / 11.8 x 9.4 x 23.6 inch

• Notes

• This is one of my DIY projects for a pure point-to-point wiring class A single-end all triode  amplification. The design started around the early 90's, the actual project started in 1994 and was completed in 1998.

  As for materials: Pure copper 2mm thick chassis cabinet, Kimber TCSS teflon 7-strand copper and Audio Note silver wiring. Holco, MILLS, IRC and VISHAY mostly non-inductive resistors. An ALPS Blue dual log 100kΩ is used as volume control. Solen PPE/ PPB/MKT, MIT PPFX-S and Hovland non-polarized audio grade capacitors. Audio Note 5KV ceramic stand-offs. SJS transformers and chokes.

  The power supply uses Solen high voltage non-polarized filter capacitors. Electrolitic capacitors are used only on the valve filament filters. Low noise semiconductor diodes configured as rectifier bridges are used on the power supply. Two 5R4GB valve rectifiers are used as soft start at the 211 high voltage anode power supply, LC filters are used on the five DC power supply lines. Some of them uses additional RC filtering.The SJS custom made 500VA power transformer uses eight secondary coils.

  The amplifier stage is self-biased and it is the unique stage using negative feedback as a result. This is a design choice. No batteries for biasing, no large electrolytic bypass caps, and get the correct stage gain. A small value audio grade Hovland cap is used as bypass to boost the high frequency response to compensate the output transformer losses. The driver and output stages uses fixed bias and no negative feedback, local or global. One analog meter per channel is used as VU-meter and as a current meter to adjust the valves BIAS. The SJS 40W, 15Hz-25kHz, audio output transformers run at 15kΩ primary.  The noise floor is totally inaudible at the speakers or using headphones, and the sound at my Castle Cherster speakers comes clean and harmonious, typical of single-end triodes.

• Net weight (2.2 lb = 1 kg)
• 55 kg / 121 lb 2.3 oz (121.145 lb)

• Author
• Model page created by Jose Mesquita. See "Data change" for further contributors.

• Other Models

• Here you find 1 models, with images and with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
  All listed radios etc. from Homebrew - RECENT but NOT Replica; Portugal