Monday, December 3, 2012

300B monoblock with interstage

This is my humble 300B with interstage transformer, made by me with a lot of helps from my shifu, the circuit very simple, WE437A as driver-interstage (5k-5k. 1:1) then 300B in cathode bias then OT  (3.5k:8 Ohm)
WE 437A is a single triode by Western Electric, old tubes, hi gain, long life, the best one for interstage amplifier.

Power supply provided by GZ 34 as rectifier - ASC x386S - Choke - Mundorf M-Lytic.
Transformer provided by local transformer factory, bifiliar and also interleaves winding.
IEC Socket, power switch, industrial standard, a gift from my friend, who's have an electronic shop in our city, Surabaya.
Resistor by Takman, will try another brands later.
Humpot by Violet (100 Ohm) will changes later with resistor in series formation, because my humpot position exactly in center position.
300b Cathode R by Dale, and can't wait for Caddock came from ebay
300b Cathode bypass by Rubycon BlackGate 100uF
437a cathode bypass by Elna Cerafine 470 uF
Binding post, female chassis RCA by CMC, this is the best for me (for my pocket actually)
Chassis using 5 mm aluminum sheet for top plate, insert plate (below the 5 mm) is 3 mm aluminum sheet.
Wood chassis material is Rosewood, 25 mm thick, a gift from my friend.
The craftman by my Shifu's assistant. The result is very good isn't it??
The result is total weight more or less 20kg each monoblock!

Sound? Very good for me, vocal and hi very extended, bass is tight because of the Full Music 300B/c Carbon Plate, My humble opinion for this tube is aristocrat sound, very polite with extended vocal and hi, maybe this Full Music 300B/c for somebody with audiophile's ears. Will change later with Full Music 300B/n Mesh Plate, because of my Shifu's influences, I'm now looking for extended bass that I can feel with my chest, not just my ears, and more musical.

Please minds, this is my personal opinion.
Bass head with tubes? yes, maybe...


  1. pak,

    mau tanya u heaternya bapak pakai AC heater? soalnya ada humpot nya....
    apakah suara hum nya tereduce dengan baik? sy baru2 sj build 300b tp pakai DC heater, tabung pakai TJ meshplate dg drive pakai 6SN7 (tp ngga pakai interstage hehe) untuk karakter suara gesit dan netral- malah terlalu "solid state" :)
    bassnya tight banget dan justru sy ingin buat agak sedikit mendayu
    rencana sy mau ganti cathode resistor pakai TDO tp nilainya masih bingung mau pakai 1kohm atau 880 ohm (yg skg pakai resistor tanpa merk 1K)

  2. hi Pak,
    Saya menggunakan AC heating untuk semua tube-nya.
    humpot adalah barang wajib untuk AC heating dalam rangkaian DHT dan dapat meminimalkan hum yang di timbulkan.

    6sn7 bapak gunakan tube apa? era saya berkecimpung dengan amp terdahulu, suara terbaik saya dapatkan dari 6SN7 tungsol black plate, RCA grey glass, Sylvania Chrome top.

    Bass tight bisa juga disebabkan pemilihan nilai dan bahan dari c coupling, bisa juga pemilihan merek dan nilai di c cathode bypass lho Pak, bypass di tube we437a saya asalnya Cerafine 220uF setelah tuning didapatkan silmic 100uF lebih natural.

  3. Hi,
    300B Monoblock Amplifier

    Wow! So nice explanation with its beautiful images. I thinks images are play more vital role for selling products. All pic are appear clear. Thanks...