Vacuum Tube Lights: Urethane Coated Plate Cap

With a generous dollop of JB Plastic Bonder left over from a set of Bafang brake sensor magnets, I tried coating the ersatz plate cap of a triode tube:

Triode - urethane coated plate cap
Triode – urethane coated plate cap

That’s the result after leaving it hanging upside-down while it cured to push all the drips to the top.

For comparison, the uncoated cap back in the day:

Triode - plate cap plug
Triode – plate cap plug

Seeing as how the urethane is an adhesive, not a coating, I’d say it looks about as bad as expected.

As with all 3D printed things, one must embrace imperfections and striations, rather than endlessly strive for perfection.

Now, if I had a resin printer …

Discrete LM3909: Green and Blue vs. Dead Alkalines

These two discrete LM3909 circuits recently stopped blinking:

LM3909 AA alkaline - Green and Blue
LM3909 AA alkaline – Green and Blue

The green LED (on the left) took six months to wear its pair of not-dead-yet AA alkalines from 2.7 V down to nearly zero.

The blue LED in the radome took two months to go from 1.0 V (!) to nearly zero. It didn’t start very bright and went decidedly dim along the way, but the LM3909 circuitry still managed to jam a few microamps through the LED.

In both cases, one of the cells was reverse-charged by a few hundred millivolts, although neither leaked.

Both got another set of not-quite-dead AA cells and they’re back in action.

Satco PAR30 LED Spotlight Teardown

One of those LED spotlights may have barely outlasted its worthless warranty, but not by much, and has been languishing on the back of the bench with “Flickers hot” scrawled on its side.

The metal base didn’t respond to twisting, so I slit the threads with a cutoff wheel:

Satco PAR30 - thread slit
Satco PAR30 – thread slit

Applying the screwdriver removed the base to reveal a silicone rubber casting:

Satco PAR30 - thread silicone
Satco PAR30 – thread silicone

The small wire emerging near the edge of the plastic case seems to be the neutral contact to the shell, with a poor enough joint to suggest it might have been why the lamp flickered when it got hot.

Some brute force snapped the silicone off at the bottom of the plastic case and broke the two wires bringing AC to the PCB:

Satco PAR30 - thread silicone base
Satco PAR30 – thread silicone base

Digging around inside produced a debris field of silicone crumbs, broken resistors, torn caps, and various other components, with zero progress toward removing the shell:

Satco PAR30 - silicone extraction
Satco PAR30 – silicone extraction

A little lathe work converted a chunk of PVC pipe into a crude mandrel supporting the mangled case:

Satco PAR30 - base cutting setup
Satco PAR30 – base cutting setup

A few millimeters of sissy cuts released a silicone O-ring sealing the shell against the reflector:

Satco PAR30 - O-ring seal
Satco PAR30 – O-ring seal

Continuing the cuts eventually revealed the three screws holding the shell to the reflector and the two wires powering the LED:

Satco PAR30 - reflector separated
Satco PAR30 – reflector separated

Chopping off the screws with a diagonal cutter freed the shell and revealed the top of the PCB:

Satco PAR30 - electronics top
Satco PAR30 – electronics top

It really does have a surprising number of components!

Those three screws connected the LED panel / heatsink to the shell through the back of the double-walled reflector. More brute force peeled the outer shell away and released the panel:

Satco PAR30 - lens assembly
Satco PAR30 – lens assembly

Each of the 5050 packages contains a pair of white LEDs with 5.2 V forward drop for the pair, at the very low test current. They’re all in series, so you’re looking at well over 60 V total forward drop:

Satco PAR30 - LED panel detail
Satco PAR30 – LED panel detail

Note that the wiring, which nobody will ever see, follows the electrical color code of white = common and gray = hot.

Perhaps I should turn the lens into an interesting art object

Discrete LM3909: Blue LED

Once again, the discrete LM3909 circuitry can blink a blue LED while running a pair of alkaline cells all the way down to about 1 V, with one cell ending at 0.2 V and the other at 0.8 V. They started out discharged to 1.2 V each during their useful life, then blinked for a month; it’s as good a use for dead cells as I can think of.

With another pair of not-dead-yet cells providing 2.4 V, it started up again:

Blue LM3909 2.4V alkaline - 042
Blue LM3909 2.4V alkaline – 042

That’s a frame from a short video taken in subdued light, just to show it really does work.

Discrete LM3909 Blue LED: Off at 1.0 V

The blue LED inside the radome got fainter as the alkaline AA cells faded away, but remained visible in a dark room until the discrete LM3909 circuitry stopped oscillating with the battery at 1.0 V. One of the cells had flatlined, with the other supplying what little current was needed.

The circuitry restarted with a pair of weak alkalines applying 2.4 V across the bus bars:

LM3909 Blue - 2.4 V alkaline
LM3909 Blue – 2.4 V alkaline

The LED waveform shows it needs about 2 V:

LM3909 Blue - 2.4 V alkaline
LM3909 Blue – 2.4 V alkaline

It’s barely visible in normal room light and strikingly bright at night.

Astable Multivibrator: Red RGB Piranha

A red LED has a sufficiently low forward voltage to run with a MOSFET astable multivibrator and a pair of run-down AA alkaline cells:

Astable AA Alkaline - red
Astable AA Alkaline – red

The red LED is actually part of an RGB Piranha, just to see how it compares to an as-yet-unbuilt version with a single red LED in the same package.

The LED drops 1.9 V of the 2.75 V from the mostly used-up AA cells:

Astable Piranha Red - 2.75 alkaline - V LED
Astable Piranha Red – 2.75 alkaline – V LED

The original 33 Ω ballast resistor showed a peak current of 11 mA in a 30 ms pulse:

Astable Piranha Red - 2.75 alkaline - V 33 ohm
Astable Piranha Red – 2.75 alkaline – V 33 ohm

Replacing it with a 12 Ω resistor boosts the current all the way to 12 mA:

Astable Piranha Red - 2.75 alkaline - V 12 ohm
Astable Piranha Red – 2.75 alkaline – V 12 ohm

The 2N7000 gate sees a just bit more than 2 V, barely enough to get the poor thing conducting, which makes the ballast resistor mostly decorative. The MOSFET datasheet puts its 1 mA threshold somewhere between 0.8 and 3 V, so it could be worse.

Keep in mind the DSO150’s 1 MΩ input impedance sat in parallel with the 1 MΩ gate pulldown resistor forming the RC differentiator when I measured the gate voltage; I’ll leave the simulation as an exercise for the interested reader. The blinks were noticeably dimmer and perhaps a bit shorter, although eyeballometric calibration is notoriously hard.

The slightly revised schematic-layout doodle stacks the transistors along the negative bus bar:

Astable wiring layout - stacked 2N7000
Astable wiring layout – stacked 2N7000

Flipping the bottom transistor over to snuggle the two timing caps next to each other would eliminate the long jumper wire and probably look better.

Astable Multivibrator: Amber LED

Adding an amber LED to the collection:

Astable AA - Amber - overview
Astable AA – Amber – overview

Because a yellow / amber LED runs at a lower voltage than blue and green LEDs, it sits atop an astable multivibrator, rather than a discrete LM3909. The battery holder has a pair of carbon-zinc “Extra-Heavy Duty” AAA cells, so corrosion and leakage pose a foreseeable hazard.

The voltage across the 100 Ω LED ballast indicates a 9 mA peak LED current, which is somewhat dim in ordinary room light:

Astable AA - Amber - LED current 100 ohm
Astable AA – Amber – LED current 100 ohm

The corresponding LED voltage says the LED runs at 2.1 V for that much current:

Astable AA - Amber - LED V
Astable AA – Amber – LED V

Something around 39 Ω should make it more visible.