UralTone Bias Tool Deluxe DIY octal probe build guide

This is instructions to build the Bias Tool Deluxe octal probe pair. The assembly guide can be used for fixing the probes too.

UralTone Bias Tool Deluxe octal probe kit- BOM

Check all the parts

Always check first that all parts are included in the delivery. If you find any problems please contact us by email or through the "contact us" form on the pages. Note that the components may look slightly different than in the photos. Also, note that the voltage specs of the parts may be higher than what is listed. Read all the notes at BOM (bill of material) carefully.

Building the Octal probe pair

Follow the order in which the images below are assembled. We try to keep component manufacturers and types the same, but sometimes we have to change the manufacturer or model of a part due to poor availability. So if a part is a slightly different color or higher voltage rating, all is good, each component has the required values marked on the side of the part.

Octal Probe has high amount of parts fitted in relatively small space used on high voltages. Follow the pictures precisely, don't leave the connecting wires too long and be sure the wires insulation won't melt when soldering close by. Doing checks with multimeter while building the probe is highly recommended.

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Measure all 4.7Mohm resistors supplied with the kit. Mark the value of the resistor. On picture only the decimals are written.

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Pick two resistors of same or most close the same value. On the picture two of 4.680Mohm resistors are selected.

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Solder the resistors on pcb. Resistors are soldered to reverse side of the board like on picture. This helps to make short as possible probe.

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Set the PCB aside. Cut the wire came with the kit on two equally long pieces. On jack end the cloth thread is cut short and the protective shield is twisted as single wire. White wire is cut shorter than red. Presolder the wire ends. Remember to set the plug shell and shrink sleeve before soldering the plug.

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Solder the red wire first.

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Then fix the ground and white wire on their places. Solder both wires.

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Heat up the shrink sleeve and tighten the tabs on plug. The idea of the shrink sleeve to recognise which probe is plugged on each channel.

Prepare the probe end of the wire. Presolder the wire ends and heat the shrink sleeve on.

Solder the wire on PCB. Follow the markings R = Red, G = Ground, W = White.

Secure the wire with tie wrap

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Check the probe with meter. Ground and Red wire has 4.75kohm resistance, Ground and white has 11ohm. (Red - White is 4.761kohm.)

Solder the jumper wire for pin 8. Leave short piece of sleeve on the wire. Check and cut short the wire end on back side of the PCB if needed.

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Solder the tube socket on PCB. PCB has silk screen of the outline of center guidance pin and pin numbering. Match these with tube socket. Be careful with the pins 4 and 5 not to burn the wire.
Cut short the pin 8 and bend the wire mounted on previous stage to take it's place. Check you have soldered all pins of the socket.

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Push in the octal plug. Notice the center guide pin and pin numbering. Align the plug same direction as the tube socket.

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Solder the connector. After soldering the the plug reversing back is impossible. Be sure all work done previously is done correct.
Heat up the pin on the plug on the bottom and push solder in on the tip of the connector. Be sure the solder is not flowing through and pool on the PCB causing short circuits. Using vice or similar tool is advised, where the provbe can be mount and soldered horizontally.

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Measure the opposite connectors for zero resistance / conductivity. Pin 8 is exception with 11ohm resistance.

Measure all pins as pairs (1-2, 2-3 ... 7-8, 8-1) for infinite resistance / no short circuits.

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When probe is passed testing, attach the wire to screw mount of the socket with tie wrap and fit two layers of shrink sleeve. Cut small piece of where the wire is coming out. Two layers ensures good protection.

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Heat up the shrink sleeve layers one by one. Probe is ready.

If you make mistakes while building the probe, best way to open it up is to crack the octal plug and remove all pins individually and using new plug. Damaged resistors are possible to replace by removing the shrink sleeve. In general, it's probably the best to make new set of probes to replace damaged one.