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Friday, November 8, 2013

UX201A Sound Processor, Part 2 : Assembly


After the presentation of the circuit in part 1 of the article series about the UX201A Sound Processor, this post will show the assembly steps.

Since this circuit needs massive heatsinks, the usual chassis with wooden frame would not work. So I designed a completely new full metal chassis style. The chassis was sized as compact as possible.

The top metal plate with sub plates for the tube sockets:

The sockets are mounted to sub plates which in turn get attached to the main plate by rubber damping elements as seen in my DHT preamps and phono stages.

The sub plate mounted into the main plate:

Pre assembled main plate:

Adding the Tango NP8 line output transformers. The connection between transformers and plate pins are already in place (done with solid core silver wire and additional insulation sleeve):

Preparation of the heatsinks:

The 3 resistors on the left side are 1.5k/25W types. They will be wired in parallel to get the 500 Ohm resistor through which the filament voltage is derived from B+. It has been split into three resistors to spread out the heat dissipation. The resist on the right is the 22 Ohm filament bias resistor.

Mounting the heatsinks to the top plate :

Wiring of the resistors. The main ground buss is also in place already (wire at the bottom):

Adding the chokes :

The chokes are nice nickel core units wound for me by Dave Slagle

View from the backside before the panel with the connectors is attached:

Preparation of the back panel:

There are two sets of outputs. The NP8 secondary has a tap for extra low output impedance.

Backplate attached to the Sound Processor:

Adding the bottom plate :


In the next articles the circuit and assembly of the power supply will be covered. Stay tuned!

Best regards



  1. As the name says: A Sound Processor which alters the sound by adding the unique distortion characteristics of the UX201A

  2. Hi Thomas,
    can you shed some info on what and where one can get the aluminum bracketing used in assemblies of your products? Thanks!

    1. Hi Dave,

      you can get them from me. Drop me an email if you are interested

      Best regards


  3. Hello Thomas,
    I know you love LCL circuit for filamnent. I have done it too, along with auto cathode bias. Sound is very good. Can I use it for Filament bias on 01A tubes ?
    Thank you and best regards,

    1. Yes you can use LCL with filament bias