Storm Door Latch Lube

Storm door latch parts
Storm door latch parts

Our old house has storm doors with brass latch bolts and brass strike plates. Brass-on-brass is nicely self-lubricating, unlike the steel-on-steel contraptions available these days, but of late our back door hasn’t been closing smoothly.

I fiddled with the door closer’s tension and release point to no avail, then (re)discovered that a dab of PTFE lubricant on the latch and strike plate makes the storm door close exceedingly smoothly. The base grease is clear and doesn’t make a black mess of things.


Maybe everybody knows that and perhaps I knew it at one time.

I wrote about rebuilding the strike pull and shaft cam of these latches as CNC projects in my Digital Machinist column. Naturally, the replacement latches available in the local hardware stores didn’t fit the door, so the simplest course of action was some quality shop time.

Analon Slide Rule

Whenever I do anything even slightly out of the ordinary with magnetics, I must drag out my trusty Analon slipstick to make sure I haven’t lost a dimension.

Analon slide rule - front
Analon slide rule - front

Go ahead, you verify that the area inside a BH hysteresis curve is proportional to power loss in a given transformer core. I’ll wait…

Analon slide rule - back
Analon slide rule - back

My recollection is that I bought it in the Lehigh University Bookstore in the early 70s, but that doesn’t square up with the Analon’s history: they should have been out of circulation by then. I’m pretty sure I didn’t get it in high school, extreme geek though I was, and it’s for damn sure I wouldn’t have bought one after graduation. Come to think of it, if the LU Bookstore wasn’t among the last bastion of Analon holdouts, where would you look?

Over the decades I’ve penciled in a few handy dimensions they didn’t think of. Unlike most of the 600 597 (plus one in the Smithsonian) Analons in the wild, this one actually gets used, so it’s not New-In-Box (which means you collectors need not suffer from involuntary hip motions). It’s also not as grubby as it looks: I didn’t spend a lot of time futzing with the scans.

Anyway, that’s called beausage and it enhances the value.

Works that way with other antiques, right?


Yeah, OK, it’s a Slide Rule Gloat…

AA Cell Dimensions

Ever wonder why rechargeable AA cells don’t quite fit in older flashlights & gizmos? Somewhat to my surprise, the dimension specs for alkaline and rechargeable cells aren’t quite the same.

At the bottom of the Wikipedia AA battery page, we find “brand-neutral” drawings (allegedly) based on ANSI specs:

  • Alkaline: 14.0 ± 0.5 dia x 49.85 ± 0.65
  • Rechargeable: 14.1 ± 0.6 dia x 48.9 ± 1.6

A rechargeable cell can thus be 0.2 mm larger in diameter, but should have the same maximum length.

Based on my collection, alkalines seem to be near their nominal and NiMH cells near their maximum. Across a four-cell layer, the difference adds up to 1 mm or so, which is enough to strain the plastic.

8-cell NiMH AA pack
8-cell NiMH AA pack

Hint: Put some paper on the negative terminal when you measure the cell length. Steel calipers are pretty good conductors and the short-circuit ratings (even for alkalines) are surprisingly high  …

When I make up NiMH packs for our bike radios, I lash the cells in place with cable ties. It’s not pretty, but the plastic cases don’t split.

Connector? Anderson Powerpoles FTW! Make sure you align them properly to mate with anybody’s radio.

Power Outlet Contact Failure

Burnt outlet expander
Burnt outlet expander

Ordinary AC power outlets have fairly robust contacts, designed to last basically forever. I have no idea what the actual design life might be, but it’s rare to have an AC outlet fail.

This one did…

It’s an outlet expander at the end of an extension cord that provides six outlets. I’d installed it at my parent’s house (I was their go-to guy for electrical things, of course) and everything was fine. One visit involved rearranging some appliances and the adapter went nova when I plugged something into it.

Me being their go-to electrical guy, I’m pretty sure this gizmo didn’t experience a whole bunch of mate-unmate cycles in my absence. Most likely it was defective from the factory, so sticking a plug in once or twice was enough to break the contact finger.

Detail of burnt socket

Here’s a contrast-enhanced detail of the outlet in the lower-right of the top picture. The broken finger bridged the brass strips carrying the two sides of the AC line in the left side of the compartment.

Blam: brass smoke!

Oddly, the fuse didn’t blow. It was pretty exciting to have a small sun in the palm of my hand until the contact finger fell to the bottom of the compartment.

The bottom picture shows the offending finger. It’s pretty obvious what happened.

Errant contact finger
Errant contact finger

I’ve read of folks applying silicone lubricant (spray, perhaps) to their AC line plugs to reduce the mating friction in the outlet. While that sounds like a good idea, I think it’s misguided: you don’t want to reduce the metal-to-metal contact area by lubing it up with an insulator. In any event, that sliding friction ensures the contacts have a clean mating surface with low resistance.

Maybe use some Caig DeoxIT, but not an insulating spray!

For what it’s worth, do you know that the durability of an ordinary USB connector is 1500 cycles? That’s far more than PCI backplane connectors at 100 cycles. Some exotic high-GHz RF connectors can survive only a few dozen cycles.

Moral of the story: don’t unplug your stuff all the time. Use switches and stay healthy.

This took place many years ago, so the picture quality isn’t up to contemporary standards.

CD V-750 Dosimeter Charger Manual

V-750 Model 5b Manual Cover
V-750 Model 5b Manual Cover

My V-750 dosimeter charger came with two (!) copies of the manual and the modification instructions (stamped JUN–1965) for adding the anti-kick capacitor.

The paperwork didn’t fare quite as well as the metal-cased charger, sporting far more mildew on the pages than I want on my shelves.

I cut the worst-looking copy right down the middle, scanned it with some attention to detail, and now there’s a nice version that looks just as bad but lacks the mildew.


CD V-750 Model 5b Radiological Dosimeter Charger Operating and Maintenance Manual with Modification Instruction Sheet

If you’re really clever, you can figure out how to sequence the sheets and print them duplexed so they appear back-to-back, then bind them into a booklet just like the original. There’s a copy of a blank inside cover, too, so you can wrap your booklet in a nice Civil Defense Yellow cover.

The schematic shows what real engineers could do, back in the days when transistors came individually packaged with a ten-dollar price tag: 1.5 volts in, 200+ volts out, one transistor. Of course, they paid attention to their transformer lessons.

V-750 Dosimeter Charger Schematic
V-750 Dosimeter Charger Schematic

Verizon FiOS: What’s the Real Price?

So FiOS has finally arrived here in the hinterlands and the latest teaser deal is $70/month for 10/2 Internet and anywhere-in-the-US VOIP. The ad mailers always tout the blazing speed (although that’s not what they offer in the teaser) and voice clarity.

But there’s an asterisk: the prices are always “plus taxes and fees”.

So I called the FiOS order line (877-896-2263) with two simple questions:

  • What, exactly, are those taxes and fees?
  • What, exactly, will they add up to each month?

After five minutes of telling the nice man everything they already know about me and giving him permission to read their own records of our account, I managed to push him off his script long enough to get a word in edgewise.

He tells me that the taxes and fees depend on my exact location and the services I sign up for. I point out that we’ve just established my address and he should know what services he’s offering, soooo what’s the price?

We go around and around:

  • He says the only way to find out is to sign up and get my first bill
  • I refuse to buy something without knowing the price

Eventually he offers to transfer me to billing, where he says (and I have no reason to doubt) that they’ll certainly tell me the same thing. Sounds like a good idea to me, if only to get to the next screen. He’s obviously miffed that I’m not following my lines in his script and just buying FiOS like a good sheeple.

I hear the usual beeps & boops, a snippet of their on-hold blather, and dead silence. Ten seconds later, the call disconnects and I get the usual “If you’d like to make a call, please hang up and dial again” message.

They don’t care. They don’t have to. They’re the phone company.

Right now we’re getting 13/2 Internet from Cablevision (aka Optimum Online) for $50 and a Verizon landline for $25.

Let’s see: slower Internet and marginally cheaper phone service, plus the asterisk. Not a compelling value proposition in our situation. But, then, we’re cheapskates.

Incidentally, the “taxes and fees” make up $10.61 of this month’s $25.09 phone bill. I have good reason to believe that if we buy two services from Verizon, the fees will add up to $20 or so. But there’s no way to find out without buying them first, of course.

I’m seriously thinking of killing the damn landline and struggling along with VOIP and our $5/month cellphone.

Update: Today’s mail brings an even better teaser with a different phone number: 877-896-5322. It’s still $70/month for a one-year “agreement”, but now with free activation and a $100 cash card and they guarantee the rate for two years. The kickbacks push it just under $60/month for the first year. Still has that asterisk, though. Not to mention that the offers just keep getting better and better … I’m sure the early adopters are astonished at Verizon’s sliding incentive scale.

Update 2: If you ignore the flyer and sign up for FiOS via the Verizon website, you get an additional $5/month off and you don’t have to deal with Verizon customer service. That brings it down to $55 plus the dreaded asterisk… I wonder what next month’s mail will bring?

Update 3: Another flyer and the offer is still $70/month, free activation, and $100 cash back. Somehow I think FiOS uptake around here isn’t living up to their expectations.

CD V-750 Dosimeter Charger Switch Cleanup

So I got a classic Jordan Electronics CD V-750 dosimeter charger (for V-742 dosimeters) from the usual eBay supplier, mostly because I’m writing a Circuit Cellar column and need a MacGuffin to talk about HV transformers and power supplies.

The charger had some corrosion on the cast aluminum (?) knobs, but seemed largely unscathed by four decades in its original box. The charging circuitry depends on a few electrical contacts and, as you might expect, those were badly intermittent.

A bit of background…

Charging contact pedestal
Charging contact pedestal

The charging pedestal has two parts visible from the outside: an outer sleeve that’s firmly secured to the case and an inner cylinder that slides within the sleeve, with springs inside the charger pressing it outward. Well, there’s a nut, toothed washer, and the bead-chain cap assembly, but those don’t count.

The inner cylinder has a transparent plastic insert crimped in place, with a metal rod protruding about 2 mm from the flat top of the plastic. That rod presses against the middle contact of the dosimeter and connects the charging voltage to the electrostatic fiber. The outer body of the dosimeter fits snugly over the cylinder to make the other electrical contact.

The directions tell you to press the dosimeter down gently to read it. A weak spring holds the cylinder outward with about 1.5 lb of force. After about 1 mm of travel an incandescent bulb (remember those?) turns on, transmits light through the plastic insert, and lights up the dosimeter scale and fiber.

To charge the dosimeter, you press down firmly and twiddle the adjusting knob to position the fiber. Pressing hard enough to force the dosimeter body down to the sleeve, another 3 mm of travel, compresses the dosimeter’s internal bellows (or plastic seal) enough to complete the circuit to the fiber; a sealed dry air gap normally isolates the fiber from the dosimeter’s external contact. A stout leaf spring holds the cylinder outward with (according to one instruction manual) 7.75 lb of force, so it takes more pressure than you’d expect to hold the dosimeter down.

Charging contact inside view
Charging contact inside view

The internal parts of the charging pedestal makes all that stuff work without any formal switch contacts. That, unfortunately, causes the intermittent operation.

The gray “wire” inside the large 7-lb leaf spring is both the 1-lb spring and the high-voltage electrical contact. The purple wire soldered to the end of the wire spring carries the HV charging potential from the circuitry.

The black and red wires connect to the incandescent bulb, which fits into the holder near the top of the circuit board sticking up vertically just to the right of the pedestal base; I removed it to reveal the other parts. For what it’s worth, the bulb holder doesn’t do a good job of securing the bulb; I have some improvements in mind for that, too.

Note the spare bulb just beyond the center bulb contact near the top of the picture. The rubber grommet securing that has turned into black Gummi-bear substance; that sucker is in there forever.

The battery’s positive terminal connects to the case; this is a positive-ground circuit!

The leaf spring hitches over two shoulders on the circuit board and presses it firmly against the other side of the spring. The curved fork fingers pressing against the brown insulating washer are firmly mounted to the circuit board and act as one side of the switch contacts.

Pedestal removed from charger
Pedestal removed from charger

When you push the dosimeter against the sleeve, the base of the cylinder slides through the ID of the fiber washer and contacts the fork fingers. Bingo, that completes the circuit, lights the lamp, and fires up the HV circuitry. The charging voltage doesn’t reach the dosimeter fiber because the leaf spring hasn’t started pressing the cylinder against the dosimeter’s innards: there’s no connection inside the dosimeter.

With that out of the way, here’s what’s needed to get the pedestal working reliably.

Get the whole pedestal assembly out of the charger, which requires a bit of wiggly jiggly action. This will be easier if you unsolder the three wires, which I didn’t do until I was sure it was absolutely necessary.

Grab the leaf spring on both sides of the bulb circuit board, pull up while pushing down on the spring’s base with some other fingers, and lift the tabs off the circuit board shoulders. This requires a surprising amount of force; don’t let the spring get you by the soft parts!

Leaf spring released
Leaf spring released

A small crimped metal connector mates the end of the wire spring to the center contact in the cylinder. Pay attention as you maneuver the pedestal out of the leaf spring: you don’t want to deform that connector too much. Or, much worse, lose it under your workbench.

There’s a rubber O-ring inside the outer sleeve that’s barely visible in the picture of the parts. The 1-lb wire spring had trouble forcing the cylinder back out through the O-ring, leaving the switch just barely closed even with the dosimeter removed. A touch of silicone gasket lube on the O-ring made it wonderfully slippery again.

The inner cylinder has wire snap ring in a groove that adds a bit of stability and maybe some contact friction inside the sleeve. You need not remove the snap ring; they’re not called Jesus clips for nothing. It’s outside the O-ring’s protection, exposed to the world.

Basically, clean everything without yielding to the Siren Call of sandpaper. What you want to do is get the oxidized metal off the base material without scarring it.

Pedestal contact components
Pedestal contact components

I applied a tiny drop of Caig DeoxIT Red to the snap ring, worked it around & around, then wiped off the residue.

The actual switch “contacts” are the wide base of the inner cylinder (to the right in the picture) and the rounded end of the fork attached to the lamp base circuit board. The contact area is broad, smooth, plated-steel-on-steel, and utterly unsuited to the job. Wipe both of them clean, add DeoxIT, wipe them clean again.

I applied another minute drop of DeoxIT to the base of the cylinder after putting everything back together, rotated it against the fork, and wiped it off. Most likely that had only psychological benefit, but what the heck.

The parts go back together in the obvious way, again taking care not to let the leaf spring bite you. I routed the wires a bit differently, but I doubt it makes any difference.

Now the charger works perfectly again!

Memo to Self: replace that bulb with nice soldered-in-place LED

V-742 Dosimeter set to Zero
V-742 Dosimeter set to Zero

Update: It seems you can actually buy V-750 dosimeter chargers new from However, eBay is significantly less expensive and you might get some quality shop time out of it. Your choice.