Thursday, April 15, 2021

Glacial movement of supplies while I bide my time


I had a quote from to produce 165 holders for an attractive price, with a production completion date of April 14 and delivery by the 21st using a medium priced shipping option. 

I was contacted a few days ago by customer service letting me know that the manufacturing partner informed them that the job will take an extra day to complete - April 15. As a consequence, upgraded my shipping at no charge to 1 day which was more than fair.

Today, when the parts should be shipping, the status remains 'in production' and not yet moved to 'quality inspection'. Hopefully they will not be further delayed. On the other hand, having shoddy unusable parts early is not a good alternative; happy to wait a bit to get good parts.


The bulbs were ordered from on April 12, listed as in stock and per their website should have shipped within 24 hours. It is now April 15 and the order is still showing 'in fulfillment' status. I can theoretically remove all the bulbs from my existing header strips and remount them on new strips in the plastic holders, but I won't have much tolerance for any that are damaged or can't be remounted. 

Friday, April 9, 2021

Experimenting with the 3D printed lamp holder prototype


I had whip off a single lamp holder for me, allowing me to test its fit and functionality before I ordered 164 of the final versions. This site offered a relatively quick turnaround, although at a higher per unit price that other fabs would charge. I would tweak the design, if needed at all, then order from a more cost efficient vendor. I also want the final product to be in white nylon, whereas the prototype only had a black nylon option.

Bulb fits between two upper wings

Opening in bottom for two position header

View of top which will fit into honeycomb cell


The process of building a lamp starts with the insertion of a two position header strip through the bottom of the holder. The strip must have round pins in order to fit in the round sockets I put on my PCB. I can use a breadboard as an anchor for the strip (and the holder above it) for the next step.

Header inserted into the holder

I then took a 2114 lamp, which has wire terminals, and placed the leads around the header strip upper pins. When the bulb is situated properly inside the two protective side wings, with the leads wrapped on the pins, I can carefully solder the bulb in place. 

Bulb in place but wires not soldered to pins yet


I then plugged the test lamp into the PCB in various positions, some with absolutely perpendicular sockets and some where the socket is tilting to the side. That would give me a sense for how sensitive the system will be to tilt, since the holder ends have to find the cell and slide into the round hole inside the cell of the honeycomb matrix. 

Final check was sliding the holder into the cell just to see whether it might hang up on an edge, requiring more curvature of the part, or if it aligns itself automatically upon insertion. 

Holder in place and bulb lighting 

Placed behind the honeycomb matrix and the lamp illuminated


While unsoldering a bulb from the header strip prior to re-using it in the holder, the plastic of the strip got soft and the pins bent sideways slightly. This left the pins at an unexpected angle, tilting in the direction of the longer edge of the holder. I was only expecting alignment issues when the sockets on the PCB were not perpendicular, leaning the holder in the direction of the short edge. 

The pins on the header strip only project out of the holder base a relatively small amount, less than I imagined. This reduces the space available to coil the wire leads and to get the soldering tip in place. I believe it is workable as it is. If I were to make a relief cut on the sides, there would be less bracing for the header strip which would aggravate any leaning tendency. 

I decided that I should straighten the sockets on the PCB as much as feasible, just to improve alignment, but don't find them critical. The holder slides easily into the opening of the honeycomb but does NOT slide into the hole. That causes the completed assembly to stand back a bit from the honeycomb, but eases the alignment requirements substantially. I think this will do just fine.

With that determined, it was time to place the volume order through 3D Hubs which knocked the price down to $0.91 per holder delivered. I expect them to arrive no later than April 21 at which point I will install all the headers and bulbs to finish the project.

Wednesday, April 7, 2021

Tested brighter 8610 bulb against 2114 - noticeably brighter but 4X the current


I have supplied the board for the IBM 1130 Console Display with 2114 incandescent bulbs, 6.3V 50ma parts. The total consumption of the board is relatively low as a result and the console lights show through just fine in a normally lighted room. 


In the same form factor and voltage rating, there is a higher power bulb - the 8610 - that consumes 200ma but is brighter as a consequence. If I used these exclusively in the console, the power requirement would zoom up to 232 Watts and draw a bit over 32A whereas the current bulbs would eat under 60W with correspondingly lower current. 


I wired up one of the 8610 bulbs and installed it next to a 2114 bulb, allowing me to visually compare the two in terms of brightness. Indeed, the new bulb is noticeably brighter but it comes at a heft price in terms of power. 

2114 on left, 8610 bulb on right


Because the brightness is sufficient with the bulbs I already used, I decided to keep them in the machine. I will make the additional 14 lights to fully populate the board using the 2114 bulbs. The 8610 remain as an alternative if I ever find that the brightness must be substantially stepped up. 

Minor issue spotted and corrected


Lamp Test failed for the Accumulator Extension Register bit 10 position. It was not the bulb, thus I needed to inspect this further and repair whatever is wrong. It wouldn't light with either the Lamp Test activated nor with a +3V signal on the input pin. 

That suggested that my problem was likely another bad solder joint. Having selected 2 ounce copper pour for my PCB, I had to deal with the higher thermal mass of the pads. It took a longer time applying heat for the pad to flow solder, while the gate lead of the thyristor would flow much earlier. I ended up with a couple of heaps on the component lead that didn't attach to the pad underneath.

Reflowing the joint fixed the problem immediately. I verified that both the signal input pin and the Lamp Test control would cause it to light.

Tuesday, April 6, 2021

Almost fully populated board tested with adequate transformer I received today


I had ordered at 6.3VAC transformer rated at 6A, which is big enough to handle the 7+A of the full board for short periods. I wired up the primary to a plug, popped it into the wall and verified the voltage of the secondary was 7.6 VAC; a bit hot but even better as a test since it draws a bit more current than we will in the running 1130 system.

Transformer rated at 6A

Wiring the transformer to the board was next on the task list - tying one side to the common of my 3V DC supply while I was at it. A quick activation to ensure nothing bad was happening, and then I could turn on the Lamp Test switch.


Due to a shortage of bulbs, until the new supplies arrive, I didn't have bulbs for every position. I got close, illuminating two of the Synchronous Communications Adapter (SCA) positions but leaving the rest of the SCA and all of the Customer Engineer (CE) positions empty. Every other position that is active on an IBM 1130 had a bulb in place.

I flipped the Lamp Test switch, which injected +3V to the control line on the board that caused all of the thyristors to conduct and illuminate their bulbs. Prior to this I had hooked up three random signal inputs to +3 just to have a brightness to compare against. The result was a bit of dimming but the transformer voltage sagged less, only down to 5.76V. I could see the current jump up initially then drop to just under 6A. As I added in the last few rows of bulbs, the final current seemed to have settled to that same level suggesting that the transformer is saturating.

Lamp Test mode

Comparison of three bulbs fully lit

The board remained cool to the touch, as did all the thyristors and the wires bringing the AC current onto the board. I left the Lamp Test switched on for quite a while, with everything remaining as it was. I am now happy to consider this board fully tested and ready for its eventual connection into the IBM 1130 computer. 

Current with three bulbs lit, full voltage delivered

Current with 147 bulbs lit, noticeable sag in voltage

Sunday, April 4, 2021

Measured bulb current draw, pleasant surprise, but purchased junk ammeter


I bought a 20A ammeter through from Uxcell, claimed to have a proper internal shunt and accurate to a reasonable degree. With the ammeter in the circuit, even with 44 bulbs installed it barely registered 1/2 amp draw. However, I was suspicious about the correctness of this given the dimming that happens with that many bulbs plugged in. I am returning it to Amazon since it doesn't work properly.


My VOM has an AC current measurement but a max range of 200ma, not very useful for measuring more than a handful of bulbs, but it did give me a baseline for comparison. With four bulbs inserted, I measured almost 7V from the supply and 172ma of draw. 

The defective ammeter on the other hand is off by a factor of 4 to 5x. As a second check, I grabbed a second VOM, one with a higher range of AC current measurement, and put it into the test circuit with 10 bulbs installed. I should see 400+ ma of current draw if my other measurements are correct. I recorded 440ma with the unloaded voltage of 7.06 dropping to 6.89VAC when the lamps were lit.

Current consumed by 10 bulbs lit by Lamp Test

Populated the board with just 10 bulbs to do the measurement

Voltage while supplying 440ma to light the lamps

Unloaded voltage of the AC supply

Gate draw is going to be pretty negligible by comparison to the lamp current. The resistor voltage divider to each gate consumes about 0.2ma of current, 34ma for all 164 circuits simultaneously conducting. The thyristor adds some microamperes to the draw, which we can ignore. 


That suggests that at full supply voltage in the IBM 1130 these will draw about 40-50ma apiece when lit. All 164 positions, if the same type bulb is used, would only draw around 7 amperes, well within the capability of the new beefier transformer that will arrive Tuesday. 

Some T 1/4 size bulbs have a spec of 200ma, others 50ma, and it is possible that I have a mix of both types in my supply. I have been measuring their cold resistance (10 ohms approximately) to verify lack of shorts, but I decided to set up a jig to test all bulbs for current draw and sort them into groups.

The consumption of the bulbs directly wired to the AC feed is different from their draw in circuit, in part because of the approximately 1V drop across the thyristor while it is conducting. I think that IBM specified 7.25VAC for its lighting circuit with that drop in mind, yielding about the nominal 6.3V at the bulb that matches the bulb specifications. 

The measurements confirmed the expectation that the entire board will consume between 7 and 8 amperes depending on the exact voltage inside the IBM 1130, with all lights illuminated simultaneously. 


If I determine that I have about 150 bulbs that draw 50ma and add 14 that draw 200ma, that would bump the board consumption up over 9 amperes but still within the short burst capability of the transformer that will arrive soon. I should look for a source of bulbs at the proper current, since each burned out bulb will force me to bump up the board load by 150ma, which would scale up the draw quite a bit over time.

As an alternative, if I could find 2114 bulbs, which are the type I already bought, that would be a preferable component to use with my console. In the end, I did manage to buy a couple dozen of the desired bulbs and thus can do a full up test of the board with Lamp Test once everything arrives here. 

Saturday, April 3, 2021

Finished first version of bulb holder design for 3D printing


This holder is designed to take a two position standard (.100" pin distance) header strip in the bottom, with the longer pins sticking up through the holes with a barrier between them. A wire lead incandescent bulb is placed astride the barrier, its wire leads wrapped around the two pins and soldered in place. The side walls keep the bulb protected and aligned. The fillet of the tops of the side walls helps insure that each holder slides into the opening in the 1130 console honeycomb cell. 

View from bottom where header is inserted

Drawing views

View from above where bulb is placed