Tag Archives: Education

Identify It! Answer for 6-3-2010

This Identify It! Challenge was a little different than normal. Thanks to everyone who DIDN’T post an answer! I knew when I posted this weeks picture that a portion of our audience would likely know exactly what this object was. Imagine my delight when one fan posted a picture of himself with his very own!

Heathkit Model 336 High Voltage Probe

Heathkit Model 336 High Voltage Probe

This item is a High Voltage probe manufactured by the Heathkit corporation as a build-your-own kit in the early 1950’s. In fact its is a model 336 “Television Test Probe Kit.” It is meant to work with multiple models of their popular vacuum tube volt volt meters. The unit pictured here was bought along with a model V5 Heathkit VTVM kit and originally sold for $5.50 in 1951! It extends the range of the VTVM so that it is possible to measure voltages up to and including 30KV.

What Its For:

This probe is meant primarily for use in servicing cathode-ray-tube based television sets. A CRT works like any other vacuum tube in that a filament heats a cathode which then emits electrons (a.k.a. the Edison effect). Since electrons are negatively charged they will be attracted to, and accelerate towards a positively charged plate. In an ordinary audio or radio tube the plate voltage is anywhere from a few hundred to 450 volts. Since a CRT is much larger it requires a much higher positive voltage in order to operate. A black and white TV might have a voltage from 7KV to 20KV depending on the size of the tube and a color TV (with its three electron guns) operates at anywhere from 20KV to 30KV. This high potential accelerates the electrons in a beam so that they can strike phosphorus on the screen which then emits the light you see. One problem, especially with older TV sets and early color sets is that if the current flowing through the tube is too high the picture tube (and other tubes relating to the generation and rectification of the high voltage) can emit X-rays. It is important to be able to measure the high voltage (in the KV range) present at the anode of a CRT in order to adjust the high voltage circuits to eliminate the chances of producing X-rays and also provide enough voltage for a bright focused picture.

How It Works:

The probe body is made of plastic that while clean and dry will not conduct electricity. The fins around the base act as a hand guard and also increase the surface area of the exterior of the probe so that a spark can only jump from one end of the probe to the other if the voltage is well in excess of 30K volts. Similar designs are used on glass insulators on telephone and antenna terminals to help dissipate the potential for lightning damage.

Inside the probe are two specially designed high-voltage / high-frequency resistors which are bolted together from end to end forming a path for electricity from the tip back to the base. These resistors are made of a carbon stripe which is deposited in a helix around a ceramic core. The value of the two resistors in series is 1090 megaohms. The entire resistor is then glazed over to seal it from moisture and insulate it electrically. Since the CRT anode voltage in a TV is pulsating at a rate of 15.624 kHz (for NTSC TV’s in the US) there is also some capacitive and inductive reactance which is accounted for in the resistors design.

The probe is designed to plug into the phono-jack style connector used on Heathkit meters of this period. The resistors inside the probe add to the overall impedance (resistance to alternating or pulsating current, i.e. A.C. Resistance) of the VTVM extending its own input impedance of 11 Mega-Ohms many times. This has the effect of adding a 100x multiplier when using the 300 Volt scale on the meter.

And More:

Since most modern electronics run on lower voltages and since CRT’s are becoming more and more rare in new electronic devices this probe is largely obsolete. However it is still useful for working on older TV’s and I have also used it in some high voltage experiments (along with a high-voltage Diode to rectify the alternating input source to D.C. before measuring.

You can learn more about Heathkit at the following links:

The Heathkit Virtual Museum: http://www.heathkit-museum.com/

Heathkit Schematics: http://www.vintage-radio.info/heathkit/

Manuals and Pictures of Heathkit Test Equipment: http://www.nostalgickitscentral.com/heath/products/test.html

A cool site about Vacuum Tube Volt Meters: http://oak.cats.ohiou.edu/~postr/bapix/VTVMs.htm

Thanks to everyone who took part (and especially to those who avoided taking part) in this weeks Identify It! Challenge.  Stay tuned for more Identify It!’s and feel free to contact us and share your own images related to science, technology, engineering, or mathematics that others can guess about and learn from.


Jeri Ellsworth Reviews our Reinventing Edison: Build your own Light Bulb science kit!

We were VERY pleased to have self taught electrical engineer, entrepreneur, chip designer, pinball aficionado, and roller girl Jeri Ellsworth review our Reinventing Edison: Build your own Light Bulb science kit.

Jeri Ellsworth in her new "Nerd Dungeon" reviewing Reinventing Edison (image by Simon Langhof)

Jeri Ellsworth in her new "Nerd Dungeon" reviewing Reinventing Edison (image by Simon Langhof)

Jeri did a review on her live stream and also did a video that she posted to YouTube.  Other than accidentally calling us Harrison Electronics in the introduction (we forgive you Jeri) she gave us a very positive review.   See for yourself:

We are very happy that Jeri had a good time with our science kit.  Here is another photo of the Light Bulb kit in action.

Reinventing Edison: Build your own Light Bulb science kit in action (Image by Simon Langhof)

Reinventing Edison: Build your own Light Bulb science kit in action (Image by Simon Langhof)

To learn more about our Reinventing Science Kits (including other kits like Reinventing Morse) click on the “Science Kits” tab at the top of our blog.  OR visit one of our social media sites like our Fan Page on Facebook:

Find us on Facebook: http://www.facebook.com/HarrisEducational

The kits can be purchased through many educational and scientific/electronics hobby catalogs such as Edmund Scientific, Educational Innovations, Science Kit, The Vision Forum, and more.  (coming to more catalogs soon!)

Introduction to the “GIMP” for Educators

(some terms are defined at the bottom of this article)

The “Gimp” stands for GNU Image Manipulation Program. The Gimp is a free image editing program that has quite a bit of power. Chiefly it works with “raster” images (also known as bitmaps) and can handle many popular file formats including JPEG, GIF, and PNG. Its great for editing digital photographs and can be used as a drawing tool if you like to use raster editors to create images. The Gimp was not created specifically to be a competitor or replacement to Adobe Photoshop though it is often compared with Photoshop and in my personal opinion can easily handle 100% of the needs of a casual digital image editor, educator, or student.

The Gimp is available for multiple platforms (Windows, UNIX, OS X, and others) and is licensed under the GNU public license including totally open source code. It is one of the most popular and well known pieces of open source software. It is supported by a large community of users and a responsive community of developers that maintain, improve, and add to the program on a regular basis. There are also forums and on line documentation to help users learn how to use the Gimp’s many tools and features. One criticism of the Gimp has been that its user interface has been a bit clunky and hard to learn or use. I agree that there is room for improvement but having used the Gimp from its early days through its current incarnation I do think that they have improved the UI quite a bit over time and I have read about plans to further improve it as time goes on. There is even a fork in the Gimp code base that arranges the user interface, buttons, and control-key sequences to be much more like photoshop for those who are expert users of that software.

Some of the common tasks that I use the Gimp for include cropping photographs, changing the size/resolution of a photograph, taking the backgrounds out of images, compositing two or more images together, and adding text annotations to images. It supports concepts similar to photoshop including layers, channels, paths, brushes and plugins. It also has some useful tools for web developers including a button generator, logo generator, and image map generator.

Educators can make use of the Gimp in three main areas:

1) A free and relatively easy to use tool to edit images that you may use when building presentations, handouts, worksheets, tests, web content, or any other digital or print media. Since it runs on all platforms and is free, you can use it at home as well as at school. So even if your school has Apple and you have a PC at home (or vice versa) you can still get work done on your own terms.

2) A free tool that will work on any platform including older machines that you can use to teach students concepts of digital photography, image editing, or as a tool for students to edit images used in their own reports and presentations. As we move more and more into the age of WEB 2.0 students are going to be asked to create presentations, web pages, social media and report and publish their projects for others to see and use. A tool like the Gimp gives them a tool that will let them get this job done AND can teach them concepts they may one day need in their careers as they are called upon to create reports, publish content to a web page, or do more complex tasks.

3) A tool for scientific analysis of digital images taken for scientific purposes. It is possible to strip out certain color bands, adjust brightness and contrast, take measurements, and form conclusions based upon image data. Color analysis of pH indicators or from some other chemical reaction comes to mind. Spectral analysis may be another possibility.

Here are some resources for Educators, or anyone else interested in learning more about the Gimp:

The Gimp’s main website, from here you can download the program or its source code:

Wikipedia’s entry about the Gimp. This page contains a number of useful links to Gimp and Digital Image related topics:

The Gimp Manual: This site is an online user manual for the Gimp:

Groking the Gimp: This site is an online version of the book “Groking the Gimp” and acts as a user manual along with some examples and tips:

Meet the Gimp: This site contains video tutorials, podcasts, and other articles that show tricks and tips of digital image editing. It is a wonderful resource!:

The GNU foundation: The Free Software Foundation

Terms used in this article:

FORK: A term that comes from UNIX. To fork means to take one input and split it into two (or more) outputs. Those outputs may then be processed differently to produce two different versions of the same basic input. In open source software, the design of a software package often forks into two different pieces of software based upon a specific user communities needs or desires. The Gimp has a few forks including Cinepaint used in Hollywood to process film, and a version that mimics Photoshop’s user interface.

FOSS: Free Open Source Software. Free as in no cost to purchase or use, also free as in freely available, and freely distributable under public license. Open Source, as in the code used to create the software is open for all to view and modify under a public license.

GIF Image: An older image format for raster images. GIF is a proprietary format but is supported by many software tools. GIF images are limited in the number of colors they may contain but do support transparency. GIF images also support simple frame based animation and can contain multiple frames.

GNU (pronounced G-NOO with no vowel sound between the G and NOO) stands for GNU’s Not Unix and is a kind of Free Software Foundation. GNU created the GNU Public License under which many open source and freeware applications are licensed. GNU is also a big part of the operating system Linux.

JPEG Image: A common digital image format. JPEG images are raster images but do not support transparency. JPEG is a very common image format on the web and almost any software that can work with images supports this format. JPEG images support compression, which means trading file size for image clarity. Smaller file sizes means shorter download times which is why JPEG has become such a popular web image format. Most digital cameras create JPEG images. (file extension .jpg or .jpeg)

Raster Image: A bitmap image made up of pixels on a grid. Each pixel has a coordinate (x,y) and a color value. Some raster images also support transparency, in which case a pixel can also be transparent. Digital photographs are Raster Images. Raster images have a fixed resolution and if scaled image data can be lost or distorted. This is in contrast with Vector images which are more of a mathematical model of an image and are thus able to be scaled dynamically without data loss or distortion. Raster images tend to be less data intensive than Vector images which is why they are more commonly used for photographs.

PNG Image: Stands for Portable Network Graphics. This is another image format that is gaining popularity on the web. PNG images support transparency and layers and can also be compressed to save file size.