Vintage Oscillograph

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Recently I obtained a vintage Clough-Brengle oscillograph. Yes, you read that correctly–the oscillograph is the predecessor of the oscilloscope. Oscillographs lack the trigger function and the calibrated vertical and horizontal scales, along with many other features now ubiquitous on the modern instrument.

First thing I did was pull the cover off to get a look at the innards.

Oscillograph - Side View

Click the image to jump to the Flickr page which includes some notes describing the various parts of the oscillograph. There’s a lot of rust and grime from years of neglect.

There is more circuitry underneath the instrument, as shown in this photo:

Oscillograph - Jumble

A cluster of components forms the sweep oscillator of the Clough-Brengle oscillograph. The radial-leaded resistors are essentially carbon rods attached to wires and painted with colors indicating their resistance.

Color code for these resistors works as follows: The body color is the most significant digit, the end cap color is the second digit, and the dot on the body is the multiplier. The colors themselves have the same meaning as today.

These resistors are probably of the +/-20% tolerance variety. They are actually trimmed; a single gash in the side indicates where resistive material was removed during production to dial in the value.

For some reason this picture reminds me of a Frank Lloyd Wright building…

I’ll post some more pictures showing the restoration in progress. If you really must look ahead and see them, take a look at my Flickr photostream.

Carbon Filament Light Bulb

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Here’s a genuine antique carbon filament light bulb. It’s 375 watts and was originally meant for 110 volts (currently in the USA we use 120 volts AC). In the photo, the bulb is running from 50 volts.

Perhaps someone out there has more information on the age of this bulb. I think it’s around 60-70 years old. It’s not older since it doesn’t have the glass seal on the top of the bulb.

This graph shows the resistance of the filament in two types of light bulbs. The blue curve shows that a carbon filament decreases in resistance as the bulb heats up, and the pink curve shows that a tungsten filament bulb increases in resistance as it heats up.

Thus, carbon filament bulbs have a negative temperature coefficient and tungsten filament light bulbs have a positive temperature coefficient.

Tungsten is the filament material most commonly used in household light bulbs.

Incidentally the curve for the carbon filament bulb stops short at 90V because I don’t want to damage it. It runs very, very hot!

Scope Clock

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Here is my first scope clock ready for assembly. The CRT is a 3GP1.

After assembly.

Nixie Alarm Clock

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This is my first Nixie clock. It uses four multiplexed tubes and includes an alarm feature which wakes me up every morning.

There is no snooze function, and the alarm will continue to beep until I shut it off.

The microcontroller is a PIC, coded in assembly. It uses the PIC’s 32KHz oscillator to keep the time.