Category: Electronics Workbench

Having put the Tek AM503 with the 4 MHz oscillation (B075593) on the shelf pending arrival of what might be the world’s last remaining NOS 2625 op amp in the “screened and tested” 156-0317-03 grade, I figured I might as well go through the adjustment procedure on one of the bench units (B064098) to reset the gain and reduce the peaky leading edges (green trace):

I conjured a low-budget Special Adapter to feed signals into the front-panel connector:

I also used a somewhat smaller resistor in place of the required 3 Ω 3 W wire-wound unit:

It need only soak up a few seconds of the degaussing signal and never even got warm, so it’s all good.

To my surprise, the square-wave output of the JDS6600 Function Generator meets the 10 ns risetime requirement:

Perhaps half an hour of adapter shuffling and trimmer twiddling later, the AM503 output looked better:

The (purple) input comes from the function generator output through a BNC tee and an unterminated foot of coax, so the leading edge ringing is perfectly normal.

With the scope input now providing the 50 Ω termination and the Hall probe clamped around one wire of a clip-to-clip pair of BNC-to-alligator-clip adapters, we’re still not talking RF-grade interconnection quality:

Even through it’s not factory spec, the output tracks the input well enough for my simple needs.

Good old Tek instruments: gotta love ’em!

In preparation for the next time a task puts my head in a dark place, I got a cheap headband LED light:

Unlike most of the others you’ll find, this one has a pair of 18650 lithium cells in the box on the back of the headband:

Contrary to what you might think, the cells are in parallel, with shorting plates connecting the battery compartment terminals. This works well for perfectly matched cells, which is not what arrives in the package.

The 3200 mA·hr capacity claimed (in one line of the product description) doesn’t match the 2200 mA·hr capacity (claimed in another line and) printed on the cells. As expected, both claims far exceed the actual 1500 mA·hr measured capacity.

The 1 A load is somewhat more than the 800 mA I measured at full brightness, but makes for easy comparisons.

I think they put the cells in parallel to reach the claimed 4-6 hours of run time, but in practice the connection discharges the better cell to match the weaker one with no assurance of equal load sharing thereafter.

So I conjured an insulator from the Box o’ Retail Clamshells:

In the unlikely event my head must remain stuck in a dark spot for longer than one cell lasts, I can move the insulator to the dead cell and continue the mission. Charging alternate cells isn’t much of a burden, either.

For unknown reasons, the (anonymous) manufacturer soldered the LED package at a jaunty angle inside the frame:

The lens pulls in-and-out to zoom the focus. The tightest setting (all the way out) projects a bright tilted square out in front, which is somewhat unsettling.

The whole affair cost less than a pair of known-good 18650 cells from a reputable supplier, so ya get what ya get.