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Monday, December 23, 2013

Making of a 801A / 211 Amplifier, Part 3: Signal Chassis Assembly


In the last post about these mono blocks I showed the assembly of the power supply chassis. Now we will see how the amplifier section gets constructed.

The metal plate with sockets and connectors:

The red jacks above the tube sockets are bias test points. At these the bias current of the tubes can be measured with a DVM.

The back side:

Mounting the transformers and oil capacitors:

Output and interstage transformers are original Hirata Tango production:

All signal wiring is done with solid core silver wire, protected by additional sleeves:

Adding some B+ and filament wiring:

Chokes, additional oil caps  and bias resistors are added on a tier which is mounted below the metal plate:

Below the driver tube socket in the top right corner there is space left to add an input transformer if needed. These amplifiers will be used with a preamp which has very high gain, so the input transformers are left out, but can be easily added later if needed.

The amp is ready to be tested:

After testing the amplifier will be inserted into it's wooden frame.

Impressions of the finished amplifiers will be shown next. Stay tuned!

Best regards



  1. danke fuer die vielen interessanten blogs!

    frohe weihnachten!

  2. Hi Thomas
    My question is what type and brand of solder
    You use for soldering signal solid core silver wires.
    This be made with higer temperature
    if compare with cooper?
    Thanks for excellent diy blog !
    Best regards

    1. Hi Chris,

      TRT 'Wonder Solder' works well for me (stupid name though)


    2. Hi again Thomas
      TRT You use is a lead free or leaded version?
      Best Regards

  3. Output tube is too close to output transformer. Don't you afraid that coating of transformer's case will be damaged by heat?

    1. Hi!
      The tube has good ventilation from the other sides. I have used such a configuration in another amp for well over 10 years without any impact on the case. It doesn't warm up much actually