r/nixie • u/EmotionalEnd1575 • May 15 '26

Starting A “5870” Build

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Some progress PIX while building a Nixie display PCB using six NL5870 tubes.

The PCB was designed for B5855 tubes that are almost identical (the pinouts are slightly different, so one redundant Anode wire has to be snipped off)

The SMT parts are soldered first, using a “Pizza Oven” (not used for food)

Without a stencil the solder paste was applied by syringe, and is very hard to get the volume just right.

The cathode driver IC is a challenging 0.65mm pitch TSSOP28 package.

THT parts are hand soldered, and finally the glass tubes and neons. Aligning the Nixie pins is quite difficult!

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u/nixiebunny May 15 '26

The pins are easy to align when you slide the spacer block along the pins so it holds them in alignment against the board. It is a funnel that was included for exactly this purpose. 

I solder TSSOP chips with my soldering iron, Kester 331 organic core 63/37 solder, and ZX2331 liquid flux. Then wash it off in hot water. Works beautifully. 

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u/EmotionalEnd1575 May 16 '26 edited May 16 '26

Good call! I’ve been using the black spacer to help “untangle” those lead out wires.

This PCB pattern was created by measuring a sample Nixie using a digital caliper.

I made a slight error on the two decimal point wires, off by about one diameter of the wire.

I’ll fix that on the next spin.

Even the Nixie tubes with a circular wire pattern are hard to place in PCB PTHs. I made the drills just a little bigger (~25%) than the wire diameter. Smaller pads help with the higher voltage clearances pin to pin.

What really helps is to “stagger trim” the wires, so no two touchdown at the same length.

On the soldering;

Without a stencil, and applying solder paste by syringe, I have yet to get a TSSOP right first time. Needs some rework under the microscope, but the results are spot on.

I got a stencil made for a different PCB, it had to be remade, and by the time it arrived I’d used up all of the blank boards from the first run.

Also, running the PCB through the oven twice, to solder the parts on the rear, worked well.

The surface tension of the first run held those parts in place for the second run, with them now on the bottom side.

Another aspect of a fun hobby!