ADJUSTED RESISTOR VALUE TO 300 OHMS FOR BRIGHTER LAMP
After comparing the LED bulb to incandescent bulbs side by side on the SAR board I put on the testbench, I decided to decrease the resistor value from 470 to 300 in order to get a more comparable brightness with my substitute bulbs.
SIZE OF LEADS PASSING THROUGH NYLON HOLDER DETERMINES TIGHT FIT
The nylon holders have a bronze cylinder into which a metal pin is pressed to fit when the bulb is installed on the SCR. The wire lead incandescent bulbs that IBM uses have very thin leads which allow the pin to fit into the cylinder and compress the wire.
The size of the LED leads is relatively enormous, completely unsuitable to pass through the cylinder because the pin can't be pushed in at all with that large wire cross section. Even the leads of the 1/8W resistors I am using are too large to allow for acceptable fit of the pins into the bronze cylinders.
MY SOLUTION IS LABOR INTENSIVE BUT WORKS
I am using some 26 ga wire to pass through the cylinders. I have to solder the wire to the resistor and LED, having cut off most of the leads from those components. It is a fiddly process but I have been able to create half a dozen test bulbs that fit onto the pins about the same as the original IBM incandescent based bulbs.
LIVE TEST WITH SAR AND CARRY/OVERFLOW UPDATED BEFORE I BUILD MORE BULBS
Once I have the SAR board resoldered into the display panel and populated with a few of the LED replacement bulbs, I will do a power on test and compared the results. Assuming they pass muster as they are now, I can then dive into the tedium of manufacturing several dozen replacement bulbs.
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