UralTone Giant tube amp kit
UralTone Giant is tube bass amplifier kit with 250W massive output power. It is based on classic British Hiwatt design from 60s / 70s. Most users use it for bass but Giant is also great for that well-known tight, super powerfu,l but still beautiful British guitar sound!
250W all tube power - build like a tank
(Right-click and select "show image" for full size photos)
Layout, schematics and BOM will be delivered with kit.
Building the amplifier can be roughly divided into three parts: populating turret boards, mounting parts to the chassis, and wiring these together. Turret boards and chassis population can both be done first, whichever feels natural to the builder. The building style of the amp corresponds to its English style. The wiring is neatly bundled and the wires run parallel to the sides of the case at 90 ° angles.
Multiple layout images are included with the kit: Layout for turret board, Layout for chassis wiring without turret board and master layout witch contains all the parts and wirings.
Populating turret boards
The Giant Amplifier has two turret boards, one for pre amp and one for power amp.
First, install all the components to turret boards to correct positions. However, do not install the power plate trimmers P10 and P11, as these cover the middle mounting screws of the plate. In the prototype, the parts were attached to the holes at the end of the pins and the wires were soldered to the side of the pin. Note the polarities of both diodes and electrolytic capacitors. Other parts can be soldered in either direction, but it does look better if the parts are soldered in the same reading direction.
Check the finished boards carefully. It is much easier to fix errors now than after boards are installed in the chassis.
Populating parts to chassis:
Start by installing the light and smaller parts first. Transformers are so heavy that the chassis is much easier to work with without transformers installed.
The exception to the order is the Can Capacitors, which are installed last, as the transformer mounting screws are below them. If you have ordered front and rear panels you should install these same time with components mounted to front and rear panel.
The installation direction of all parts, the screws used with their dimensions, etc. are marked in the layout drawing. Tube sockets and turret boards are installed with M3 screws, Can capacitors and tube heat shield with M4 screws. Transformers mounting screws are M5 and M6.
Note the installation direction of the tube sockets: The octal sockets of the power tubes have a guide in the middle pin. Noval sockets (pre amp tube sockets) have a gap between the first and last pin. Check their position in the layout image. Octal bases in particular may slip 180 ° when rotated into place.
Transformer screws uses fairly large washers. These are there to ensure that the transformers do not tear apart from the chassis if the device is crashed.
Once all parts are installed, solder all components that will be installed directly to the chassis. These include resistors and capacitors for the front panel pots and jackets, as well as resistors for the power tube sockets. The ground rail of the power tubes runs about 1cm above the solder lugs of the tube socket. All braided wires (filaments, transformer primary and secondary) are marked in the illustration.
Finally, route the transformers according to the turret-free layout. The figure includes all wirings between the parts mounted on the frame. Always carry the cables close to the frame, this acts as interference protection. The wires of the plates and screen grids of the power tubes run in the air, away from the rest of the wiring.
Cables soldered to the turret board are left long enough to wait for final wiring.
Attach the turret plates to the chassis and solder the trimmers P10 and 11 in place. Cut and peel the wires to the appropriate length. For PVC-insulated cables, you should put a small piece of shrink stocking to prevent the wire from melting through the insulation when soldering off. The wiring of the preamplifier tubes is kept far apart, at different levels to avoid oscillations. Solder the components between the turret plates and tube sockets and the front panel potentiometers. Installation is complete!
When the assembly job is complete, check all connection at least twice before turning power on. Pay attention to the polarity of the components, eg electrolytic capacitors may explode if voltages are applied to them in the wrong direction. You can also check the multimeter for possible short circuits between the positive terminals of the filter hooks and the body by ohmic measurement. The meter reading should increase from an initial short circuit (after charging the capacitors) to several hundred kilo ohms.
The first power up is done without tubes. Before turning on the power, connect either a dummy load or a speaker to the speaker output and turn the front panel pots to zero. Turn the end tube bias trimmers to cold position by turning them fully counterclockwise. Install the mains fuse and switch on the power. Check that heater voltage at all tube sockets are correct. Reading should be 6,3VAC +/-10%.
Turn off the device and install the anode voltage fuses. Turn on the power. Check B +, B + / 2, B + / 3, tube glow and bias voltage. Check the bias voltage on all terminals of the terminals (pin 5). The no-load switching voltages are higher than those mentioned in the layout diagram. If the fuses blow, the voltages are missing or abnormally low, etc. turn of power immediately. and check all connections and components again. NOTE! Always measure the voltage of the filter capacitors to make sure the device is de-energized before handling it.
If all goes well, turn off the power and install all tubes. Turn on the power and wait for the tubes to warm up. Adjust the bias currents of the end pipes according to the layout diagram. The measurement takes place over the 1 ohm resistor of the ground rail and each end tube. Check the voltages at the tube sockets. If all goes well, plug in an audio source and start enjoying your new amp.
If the amplifier does not sound or operates abnormally, turn off the power immediately. Carefully check the connection again. Use plenty of time, at least 30-60 minutes / check. You can also ask a friend for help - sometimes it can be helplessly blind to their own mistakes.
The prototype of the images differs slightly from the kit: There may be slight deviations in the wiring and layout. As the name implies, various implementation options have been studied and tested in the prototype. The kit also does not come with 2mm banana connectors soldered to the tube sockets, nor the shielded Abiko connectors used for the mains and standby switch and the IEC connector body. However, the images are useful for creating the right kind of structure. The final amplifier is always built according to the instructions provided with the kit.