Ordering Bulbs
The PDP-12 uses 120 tiny lights in its console -- here's an edited still from one of our demo videos showing the PDP in operation:
If the PDP were built today, they would almost undoubtedly use LEDs due to their longer lifecycle and other properties (assuming the machine was otherwise and inexplicably unchanged!). However, during the 1969-1972 era when the PDP-12 was being built and sold LEDs were only just coming into their own for use in devices, most commonly as the well known red seven segment displays in calculators. Many of these were so small (due to manufacturing and cost constraints) that they were paired with magnifying lenses (now I understand the vintage calculators of my youth so much better). In any case, LEDs were not seen to be as having enough brightness, economy, reliability, aesthetically pleasing characteristics, or some other desirable property, so the PDP uses small incandescent bulbs.
Of course, over the course of 50 years, incandescent bulbs fail. And of course, the specific bulbs used are no longer available! We are not sure exactly which of our bulbs are burned out, although we know at least one in the address row (bottom left) is burned out. We'd like to replace the burned out ones in the short term and eventually replace all the bulbs.
We want our PDP to operate authentically, but we are not especially concerned with acquiring "period" components, which makes things quite a bit more practical. Previous restorers have used the tiny incandescent bulbs that are sometimes used for model railroad lighting, but at $3.45 per bulb we decided to go in a different direction, specifically these bulbs based on the recommendations of Michael Thompson of RICM.
The bulbs have been ordered, so look forward to seeing a post on replacement in the future!
If the PDP were built today, they would almost undoubtedly use LEDs due to their longer lifecycle and other properties (assuming the machine was otherwise and inexplicably unchanged!). However, during the 1969-1972 era when the PDP-12 was being built and sold LEDs were only just coming into their own for use in devices, most commonly as the well known red seven segment displays in calculators. Many of these were so small (due to manufacturing and cost constraints) that they were paired with magnifying lenses (now I understand the vintage calculators of my youth so much better). In any case, LEDs were not seen to be as having enough brightness, economy, reliability, aesthetically pleasing characteristics, or some other desirable property, so the PDP uses small incandescent bulbs.
Of course, over the course of 50 years, incandescent bulbs fail. And of course, the specific bulbs used are no longer available! We are not sure exactly which of our bulbs are burned out, although we know at least one in the address row (bottom left) is burned out. We'd like to replace the burned out ones in the short term and eventually replace all the bulbs.
We want our PDP to operate authentically, but we are not especially concerned with acquiring "period" components, which makes things quite a bit more practical. Previous restorers have used the tiny incandescent bulbs that are sometimes used for model railroad lighting, but at $3.45 per bulb we decided to go in a different direction, specifically these bulbs based on the recommendations of Michael Thompson of RICM.
The bulbs have been ordered, so look forward to seeing a post on replacement in the future!
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