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Saturday, February 1, 2014

Making of a 300B Amplifier, Part 2 : Amp Assembly


In part 1 about the single ended 300B mono blocks, I showed the assembly of the power supply. This post shows the assembly of the amp chassis itself.

The amp chassis are constructed in a similar style as the PSUs. Output transformer, interstage transformer, capacitors and tubes are visibly mounted on the top plate. The rest is going inside the wooden enclosure, mounted on a sub assembly:

That's the two filament chokes, one for the 300B and the other for the driver tube which can either be a 10Y or a 801A. And a B+ smoothing choke for each stage. close to the front plate an input transformer is mounted to give enough gain with the low mu driver tube.

The top plate carries the transformers, caps, tube sockets and bias resistors:

The photo shows it with all the signal wiring completed. I chose some transformers form my stock of original Hirata Tango. The output transformer is a very rare permalloy core NY-15-3.5S:

The NC20 serves as interstage transformer.

The sub assembly inserted into the frame and pre wired:

The top plate added and wired up:

The finished mono block:

The right side with the driver tube and capacitors, varnished in a beautiful metallic bordeaux red:

The left side showing the transformers and Western Electric 300B output tube:

Some views from different angles.

The top side:

The driver tube, here a RCA 801A:

The amp equipped with a globe UX210 as driver:

The output tube :

Stay tuned for part 3 with photos of the entire set of 4 chassis and a first listening test.

Best regards



  1. would you care to compare the sound of this amp with your older 6N7 driven 300b amps? differences? thnx.

  2. Hi!
    It is difficult to compare the sound since I haven't heard the other amp in several years. These new mono blocks are anyways in a completely different league. Much better transformers, directly heated driver stage, better power supplies. The materials cost of these new amps is 4-5 times that of the older amp.

    Best regards ... Thomas

  3. what is the price range of this amp?

  4. Another beauty! BTW, where did you get all the L-brackets (with pre-drilled holes) used in your builds?


    1. Hi Jaz,

      these are from a local supplier. They are available through me.

      Best regards