CTH Instructions


Before you start

Please pay attention. This amplifier is built on a small board with over 150 components. It is easy to make a mistake in part location or orientation. Take your time and read the website. It tells you what to do. In every instance during the prototype phase where the builder has put the right parts in the right places with the correct orientation the amp has come alive on first power up.

Common Mistakes to Avoid

  • Reversing the UF4004 diodes (see picture below).
  • Reversing C5P and/or C10P (see picture below).
  • Putting transistors in the wrong place (see images under Transistor Locations).
  • Using the wrong class transistors. If you use other than "C" class BC550/560 or other than "25" class BC327/337 your amp may fail to function.

The Compact Tube Hybrid is designed to fit the Hammond 1455K 1202 aluminum case. The board is 120mm x 75mm and fits exactly into this case. You can print silkscreen images of the entire board from these links:

Board Silkscreen Images

CTH Board Silkscreen (150dpi PNG) CTH Board Silkscreen (600dpi PNG)
CTH Board Silkscreen (300dpi PNG) CTH Board Silkscreen (PDF)

It's a good idea to study the board and components. Also, look at the schematic diagrams to locate each part on the layout. Measure each resistor before you install it to make sure that you're reading the code properly.

These two diagrams show you exactly where the different transistor types are located. There are so many transistors on this board it is easy to mix them up. Please use these diagrams to get this right the first time.

Transistor Locations

CTH Transistor Locations (JPG) CTH Transistor Locations (PDF)

These diagrams are courtesy of Ric Lee.

Board Assembly Instructions

The board is very compact with a high density of components. Note that some of the resistors are tombstoned. Pay attention to their part labels. Take your time!!!!

Have the components specific to your build in the parts box.

Warning: Don't ignore the C5P/C10P section below.

Solder the components to the board from lowest profile to highest, roughly in this sequence:

  1. Resistors and diodes (flat placement first followed by tombstone placement). Do not install D5H yet.
  2. Mount vertical diodes with cathodes up and anodes down, like this:
    CTH Vertical Diode Mounting
  3. Transistors and IC2S (TLE2426). Mount the transistors low to the board to make vertical space for the off board components.
  4. Film capacitors, trimpots, opamp sockets, and connectors.
  5. Small electrolytics, K1E, L2H, D5H. See tweak for C3H.
  6. Tube socket.
  7. PS regulators and their heatsinks.
  8. LED wiring if you will be lighting the tube.
  9. Large electrolytics C5P and C10P (see below before you do this).
  10. Install the Opamps. Be sure to get the correct orientation. Note that the dual opamp goes in between the two output buffers.

Mounting C5P and C10P

The first prototypes had these caps at 16mm diameter. But, because the enclosure is so small these caps had to be tilted inward to make room for the top to slide on. These parts were changed to 12.5mm diameter parts. They should be mounted towards the center of the board as shown in this drawing:


CTH - Mounting C5P and C10P

Clean up the solder flux residue from the board with isopropyl alcohol (or electronics flux remover) and a brush.

Inspect all solder connections carefully, using a magnifying glass, to make sure there are no solder bridges or cold solder joints. Use a multimeter in ohms scale to check for short circuits. Correct any mistakes before proceeding.


Casing Assembly

Use these dimension diagrams to locate and drill holes.

Dimensional Drawings

Panel Dimension Drawing (JPG) Panel Dimension Drawing (PDF)

The PDF version of the file is not a scale template and shouldn't be used as a scale drawing for locating holes.

  1. Locate and drill or punch the holes in the top plate for the tubes.
  2. Locate and drill holes in the front panel for the headphone jack and volume pot.
  3. Locate and drill holes for mounting the transformer, power inlet, power switch and fuse, and input jacks on the back panel.

Dimension drawings courtesy of Chris Forster.