UralTone Princeton Reverb AA1164 - Build Guide

UralTone Princeton Reverb AA1164 - Build Guide

The Princeton Reverb is one of the most versatile amplifiers made by Fender. It has just enough power for various purposes, great-sounding reverb, and a gorgeous tone. Among other blackface models, the Fender Princeton Reverb set the bar high in 1964, and only a few others have exceeded it. In addition to its great qualities, it's also a really pleasant and easy amplifier to build. The chassis is spacious, and the layout is easy to work with.

In this article, the stages of construction are outlined. Note that not all details are reviewed, and the architects' idea is mainly to familiarise the builder with its main features. The assembly is done by using the layout picture and BOM. The pictorial guide works as additional help to understand the assembly process and as well the correct order of it.

When building, always follow the layout picture and parts list. It's always the most up-to-date version and connected to the parts kit supplied. Availability of components, etc., may cause changes. Over time, there will always be improvements or changes as well. The layout picture and the parts list included with the kit are always the correct ones to follow and the most recent version.

Princeton reverb - Layout

Princeton reverb - BOM - bill of materials

Princeton reverb schematics (google search link)

Instructions for measuring and startup

Soldering instructions

Identifying components

First, always check that all parts are included in the delivery. If you find any deficiencies, please get in touch with us by e-mail. Please note that the components may look slightly different from the photos. Also, note that the voltage ratings of the parts may be higher than what is written in the list. We try to keep the models of the components consistent, but sometimes we have to change the manufacturer or model of a part due to poor availability. If a part is a slightly different color, don't panic; each component has the necessary values marked on its side. Read the notes on the part list carefully.

Building the amplifier involves three stages: installation of the parts to be attached to the chassis and their initial wiring, placing and soldering of components on the PCB board, and installing the PCB into the chassis and completing the wiring. You can complete the first two stages in any order that suits you. However, we recommend that you follow the order of the images below.

Start by fitting all components and parts which are attached to chassis. Mount the small parts first, this makes the work bit more easy when the heavy transformers are fitted last.

Note: Unlike in the pictures, the chassis in the kit is no longer supplied with pre-soldered grounding wires. The new chassis comes pre-drilled with holes for attaching screw-mounted solder lugs included in the kit. If desired, grounding points can still be soldered to the chassis. Instructions for this can be found at the end of the article.

Fasten the small parts of bottom face of the chassis:

• 6x spacers with M3x5 screws
• 3x rubber grommets
• 4x Noval-sockets (preamp tubes) - Note the orientation, space between pin 1 / pin 9 points towards two'o clock. Fastening by M3x6 screws.
• 3x Octal-socket (output and rectifier tube) - Note orientation, the guide pin with slot on center of the socket (between pin 1 ja pin 8) points towards four'o clock. Guide the ground wire in the solder lug 8. (See picture below:) Fastening by M3x6 screws.

Cathode - ground wires guided in.

Fasten the parts to back panel. The panel is attached by the parts.

Rear panel parts:

• 4x RCA-connector.
• 2x Jack.
• Mains switch
• 2x Fuse holder

Swich mounting in detail - use star washer and nut between the switch and chassis.

Fasten the front panel parts. As well as on rear, panel is attached with the components.

Mount:

• 6x potentiometers. There's no star washers between the potentiometers, except the SPEED potentiometer, which is supplied with one (second potentiometer from left). Note: Alpha potentiometers are fitted with the guide pin for locking the potentiometers in right position. This pin is bit too tall, so cut approximately half of the length of it. Make sure the guide is flush with the front panel. Pin is made out of cast aluminum so it breaks easily.
• Pilot light. This is bit tricky and tight with the space to assembe. If the pilot light is supplied with the large star washer, fit this one between the chassis and body of the light. This way tightening the nut is easier. Try to secure the nut well: if the nut is loose and the jewel is tightened too much, replacing the bulb will be easier. With loose nut, the jewel won't come off and the nut opens instead. This then requires opening the amplifier. Keeping the nut tight and jewel loose, switching bulb can be then done without of opening the amplifier.
• Leave the jacks uninstalled for now

When light parts are done, continue with the transformers. First check the mains transformer screws for proper tightness. The tolerances over here are quite large, so you may need to reopen the screws to make the transformer to go through the chassis. If needed, reopen the trouble corner and reposition the screw. Note: mains transformer is fastened by separate M4 nuts and large washers. (check the picture below)

Attach the reverb and output transformers to chassis and guide the wires through the rubber grommets. These transformers are secured with M4 screws and nuts.

Mains transformer seen on outside: the nuts holding the core and end bells are on outside of the chassis.

Project should look like this by now.

Fix the mounting band of the can capacitor with two M3X6 screws. Leave these loose for now for some free movement. Press the can capacitor in the holder, see the orientation of it. Guide the ground wire in the common negative solder lug.

Note the mains transformer mounting from bottom side: Use large washers under the nuts.

Mount the screw holding the can first. You can bend the lips bit inward, if the screw is too short. When the band is tightened, tighten the screws on chassis side. This order of assembly prevents crushing in the capacitor sidewall.

Prepare the mains wire: Peel off the outer insulator within the distance of 25-30cm, as so the blue wire can be soldered to mains switch. Do the estimation with help of the chassis. Be generous, removing clipped in strain relief without the proper tools is difficult. Over here few extra centimeters is good investment, excess wire can be clipped off later on.

Cutting the mains wire is exact work. Don't cut the insulator of inner wires. By bending the wire in tight angle and cutting carefully the outer insulator usually tears open without of getting too deep. Going round the wire the insulator is then finally cut. If you cut the inner wire insulators and expose the copper, cut the wires and shorten the wire another 30cm. Do not use wire with damaged shielding.

The strain relief need a tool for fitting but can be done with common tools: link to guide

The project is progressed for starting soldering. On following, the wires from the transformers and mains wire is soldered to chassis mount parts.

Start with the reverb transformer. Leave the red wire unsoldered.

The wiring of the kit resembles the same style used on old vintage Fenders. The lenght of wire is "right", not too short as direct line between two points nor too long to fill up the chassis by rat nest of wiring. Use the curvature of wire for nice curvy wiring all over.

Solder the speaker output wires of the output transformer. The layout picture doesn't have the black wire between the jacks, but you may solder this. This ensures the ground connection if the nut of the jack gets loose. Note the jumper on switching jack on left. The wiring is done by using the excess wires cut from transformer wiring. This reusing of wires keeps the colors and gauges of the wires uniform. The solder lug of green wire of external speaker can be left unsoldered now. There's another wire to be soldered here later.

The blue and brown wires are soldered to output tube sockets. Solder as well as the ground wire.

The blue wire of the mains cable is soldered to mains switch and brown one to solder lug on side of the fuse holder. Use shrink sleeve on the lugs of the mains switch.

Note: the wiring of the fuses are routed towards the back. The fuse holders are covered with shrink sleeve and this routing enables covering the fuse holders without of removing the wires. (this is done later, not now)

Solder the wires coming out from the mains transformer:

• Red (thin wire) pair to rectifier tube socket pins 4 and 6. Continue with the same excess wire from the pin 4. This wire is later soldered to circuit board.
• Yellow (thick wire) pair to rectifier tube pins 2 and 8. Use the second excess wire from previous step to continue the wire to fuse holder side pin. Solder the rest of this wire to top connection of the fuse holder. End of this wire is soldered to fruit board later.
• Yellow (thin wire) to common negative pin of can capacitor.
• Green (thick wire) to pilot light solder lugs. Use inner pair of holes, make sure there's no solder bridges to shorting to light body.
• Black and white (mains in) wires to mains switch to center pair of the solder lugs. Insulate the soldering joints with shrink sleeve.

Important Note: Sometimes manufacturers change the color codes of transformers without our knowledge. Always check the correct wiring from the transformer label or the paper inside the transformer box, and refer to the layout picture for guidance.

Project should look like this by now.

Close up of heater wires on pilot light.

Solder the output tube socket grid stopper resistors, the 220k bleeder resistor of can capacitor and the return line resistor of 220k on RCA connector.

Solder the jumpers and the resistors back of the potentiometers. (Note: the third potentiometer from left misses the jumper on the picture above.) Alpha potentiometers have usually some grease on the back cover and this needs to be removed first. Use isopropanol, alcohol etc. and wipe the backs of the potentiometers. After this sand of file a small area where to solder.

Input jacks are easy to prepare outside of the chassis, using the chassis as bench. Fasten the jacks as in layout and solder the resistors. (Note: If the solder you use has plenty of flux and spits this all over, cover the panel before soldering.)

Mount the pack of jacks.

Chassis preparations are now done and this can be set aside now.

It's possible to assemble the circuit board per type of component or low components first order. The later is better, because the parts are pressed against the board when it't turned aroud for soldering. On following pictures, this technique is used.

To keep on track the build, mark the parts used to printed BOM.

Some of the pads are shared, so solder only those which ones aren't populated later on with another component or wire.

Cut the wires of the components installed, both soldered or non soldered. Make sure the wire is short enough, cut in the area of pad.

Populate more components, bit higher ones than previously.

Keep going...

Until all components are on board.

You may solder the wires according given lengths on the layout picture or solder the wires when the board is attached to chassis.

Fasten the board to the chassis by six M3X5 screws. Guide the four ground wires in the eyelets on top edge of the board. Solder the red wire from rectifier tube, red from reverb transformer and red wire from anode fuse holder to board. The last wire is continued there from to can capacitor.

Solder all wires on back panel side from the board to tube sockets and connectors. Follow the given lengths of the wires. Route the wires parallel to chassis for protection of interference. Don't run the wires parallel, specially don't mix the white gate wires with brown anode wires. If wires are crossing, aim for right angle crossing for minimum crosstalk. Mark all wires soldered to layout picture. Note the V2 socket of two wires across the socket.

Solder the wires on from panel side. Keep the tremolo wiring far from the signal wires. Note the VOL-TREBLE-BASS potentiometer wiring in between. These are run on corner of the chassis and aren't visible in the picture above.

Solder the rest of the wires between the can capacitor and board and the 18k resistor on the cap.

Remember to solder the screen wiring of the output tubes.

Finally solder the heater wiring which is routed above the tube sockets.

Cut the green heater wire in two equal pieces. Solder the ends of the wires to lugs 4-5 and 9 of V1 and twist the cable in pair until it reaches the socket of V2.

Solder a new wire and the wire from the V1 to pin 9 of V2. Solder the wire from V1 to pin 5 of V4. Solder the new wire to pin 4 of V2 and continue the wire to pin 5 forming a bridge between.

Twist the new pair until reaching socket V3 and so on.

Use the large shrink sleeve on the fuse holders as on picture.

Solder the 100ohm heater balance resistors on the lug on chassis and guide the other ends to pilot light lugs. Solder the resistors and heater wire ends. (Note: The picture is taken from TV-Reverb. Princeton Reverb does not have / use choke.)

Heater wiring is now done.

Attach the potentiometer knobs, insert the pilot light and screw in the jewel. Do not over tighten the jewel. Install the fuses on the holders with given specs.

The amplifier installation work is complete. Next, following the layout image, check that all the wiring has done right and that the parts have been laid out correctly. Go through the connection wire by wire, part by part, and mark the checked part on the layout picture.

The check list for powering up and measurement points values is found here: 

https://docs.google.com/spreadsheets/d/1CRP6kfBlP8VWHthzhgFmR605qaoRH0X6vjR967P3Yy4/edit?usp=sharing

Follow the instructions of the opening page and look the measuring instructions of the tab of the Princeton on bottom left corner. Turn all potentiometers and bias trimmer to zero. (Bias zero is the most negative voltage.)

When everything is correct, measure with a multimeter as well as the integrity of the grounding and rule out short circuits in the power source:

• Measure using the resistance range of the multimeter: One probe to any part of the chassis frame and the other to the negative lug of the capacitors C1, C2, C7, C8, C9, C18 and the common negative terminal of can capacitor, the grounds of the potentiometers / black wires and the bodies of the jacks. The results should read zero ohms. 
• Measure in the resistance range of the multimeter: one at a time, measure the resistance over the positive poles of the can capacitor and the chassis. In this measurement, the resistance is small at first, but settles to several hundred kilo-ohms. Make sure to wait for the meter to settle. A small resistance, zero or only a few kilo-ohms can be a sign of a possible short circuit, which should be looked for before connecting power.

When the measurements and checks have been done successfully, you can connect the power to the device. First, install the fuses and the rectifier tube in place, the other tubes are left uninstalled. Measure the voltage from the ground and positive poles of the multi-tap capacitor. The unloaded voltage is approximately the same at all positive poles and at this stage well above the results of the measurement points marked in the layout image. If at this point there is no voltage on the capacitors, the device smokes, sparks, or does something unexpected, turn off the power. Note the headroom adjustment doesn't response well when there's no tubes loading the power supply. 

Before troubleshooting, make sure by measuring that the capacitors of the power source are de-energized and the device is disconnected from the mains. The layout picture also shows the AC voltage measuring points. If necessary, these can be measured in the 1000Vac range of the multimeter if there are problems with the device. Of these, those marked with one arrow are measured relative to the ground, and those marked with two arrows are measured between the arrows.

Install the rest of the tubes and connect a speaker or an artificial load to the output. Turn the knobs to zero. Turn on the power. Let the amplifier settle down for a few moments and measure the voltages at the measuring points. At the same time, make sure that the amplifier does not do anything unexpected.

Measuring points 400V, 325V, etc. are marked in the layout picture / voltage map. The values ​​of these measuring points are measured relative to the ground, i.e., the black measuring head of the multimeter is attached to the body of the device, and the measurements are made with the red one. It is advisable to even sit on your other hand while you make the measurements. Use the 1000Vdc setting as the measurement range and allow approx. 10% deviation from the given measurement results. 

The voltages at the measuring points are always affected by the dispersion of the tube parameters and the differences in current consumption. Another factor that changes the results is the magnitude of the mains voltage. This can vary between 220-240Vac, which is easily seen in the measurements. It is better to check the voltages more as a whole and allow them to slide in one direction or another. Large deviations in a single measuring point when the others are in place can reveal, for example, the wrong size of resistor on the PCB. You should also rely on your ears: If the amp sounds bad, something is wrong.

Note: If you measure voltages without tubes, the voltages with the mains transformer unloaded are always higher. Except for alternating current measurements of the mains transformer, always measure the voltages with the tubes.

When the measurements are done to an acceptable level, the amplifier is ready to be fitted in the cabinet. The details of this is not covered here, but here's some things to consider:

• Priceton kit is supplied with the parts for Fender style reverb tank wiring. Instructions of the assembly is found here: Fender -style reverb tank wire build guide
• The speaker cable included in the kit resembles the ones used in Blackface amplifiers.
• Rever tank needs to be enclosed to bag intended for the purpose. This prevents the feedback in cabinet. The bag can be bought as ready or diy it out of same tolex or other piece of cloth.

Good luck and happy playing with your new amplifier!

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Grounding Points to Be Soldered to the Chassis – Instructions

Soldering to a metal enclosure requires careful preparation and high-quality tools to achieve a successful result. Start by cleaning off any grease or impurities from the areas to be soldered by using isopropyl alcohol or similar. Mark the solder points, for example, with a marker. A circuit board can be used to help precisely locate solder points aligned with the front panel.

The zinc coating on the metal enclosure prevents solder from adhering, so this surface treatment must be removed for the solder to bond properly. Sand an area about one centimeter in diameter at the marked points until the zinc coating is completely removed. A rotary tool (such as a Proxxon or Dremel) with a cylindrical sanding attachment is well-suited for this task.

First, heat the chassis alone and apply solder to the joint. Use flux if necessary to improve solderability. Do not attempt to solder the wire immediately—less heat loss at the soldering point makes the process easier. Once the solder adheres to the chassis, add the wire to the joint and apply a small amount of additional solder.

The quality of the tools is particularly important for this task. The soldering station should have a thick-tipped iron to minimize heat loss and sufficient power. We recommend testing soldering on a single point first to ensure that it works before proceeding to prepare the entire chassis according to the instructions above.