The entire family of CD V-710s. From left to right El-Tronics SID-1 CD V-710 Model 1, Jordan Model 2, Victoreen Model 3 Victoreen Model 4 and Victoreen Model 5. Click Photo To See Larger.
The CD V-710 is one of the early issue Civil Defense instruments. The only documented date I have seen in relation to this instrument is 1955 from a Jordan Model 2 manual that has a copyright date of 1955 on the back cover. The CD V-710 was superseded by the CD V-715 when it was issued later in 1962. The entire family of CD V-710s went through disposition in the 1960s. Most of the CD V-710s found today have had the labels defaced and the "CD" logos marked over. This was done during the disposition process. (See Below) The CD V-710 was manufactured in both metal and plastic cases. The early CD V-700 had one model with a plastic case as did the CD V-720.
The CD V-710 is a high-range radiological survey meter (not a Geiger counter) that reads only Gamma radiation. The range of the CD V-710 is 0-50 Roentgens per hour. The scale of the meter reads in 0-0.5, 0-5 and 0-50 R/hr using an Ion Chamber detector. All of the 710s use various combinations of D-Cell and 22.5 Volt batteries. The CD V-710 Model 1 might be the most hard to find of all the CD meters. The other models of CD V-710 are fairly common. I won't go into detail about each CD V-710 model on this page.
The CD V-710 and CD V-720 are very high-range gamma radiation detecting instruments. THESE ARE NOT GEIGER COUNTERS!
This is the CD V-710 Model 1 or El-Tronics SID-1. Notice the manufacturers model number SID-1 is printed on the side of the case. The CD V-700 Model 1 and Model 2 also have the manufacturers model numbers as part of their identifications but the later CD instruments are all identified by the CD V numbers alone.This unit is similar in build to the CD V-710 Model 2 by Jordan. I've seen some photos of other types of El-Tronics Geiger counters and they all appear to have the same type of huge cast iron handle that this meter has. The huge handle makes the zero knob virtually inaccessible. The 710 Model 1 and Model 2 both have all metal cases where the 710 Models 3-5 all have plastic cases. This El-Tronics unit takes no less than 5-22.5 volt batteries and 1 D-cell to power it. This unit did have a CD emblem on the case but it was scratched off and the paint touched up with spray paint.
In March of 2006 I got a partial CD V-777 kit consisting of a this CD V-710 and a CD V-720. This is one of the nicest items in my collection. It even still has the original batteries and the strap with it. A very nice example of the set of items that came with CD V-710s when they were new.
Here is a good example of a CD V-710 Model 4 that has gone through the disposition process. The old mid-50s era meters are commonly found in this condition. The CD emblem and identification label have both been painted over on this meter. I have seen some of the plastic case CD V-710 and CD V-720s that have had the ID labels burned though with a soldering iron but it seems like most were painted like this. To see the document describing the disposition process click here. The document is in Adobe Acrobat pdf format.
This is the CD V-720 family. From left to right in the photo: Chatham CD V-720 Model 1, Victoreen Model 2, Landers Frary and Clark Model 3 and a Victoreen Model 3A. Click photo to see larger.
The CD V-720 is one of the early issue Civil Defense instruments. I haven't been able to find an exact issue date for the first CD V-720s. The first 720's were originally issued in the mid-1950's with the CD V-710. The Victoreen Model-2 is the only CD V-720 that I know of that was manufactured with a plastic case. The early versions of the CD V-720 (Chatham and Victoreen Model-2) were declared obsolete and went through disposition like the entire family of CD V-710s. Many of the early CD V-720s that are found today have had the labels defaced and the "CD" logos marked over. This was done during the disposition process.
The CD V-720 is a high-range radiological survey meter that can discriminate between Beta and Gamma Radiation but only measures Gamma. The range of the CD V-720 is 0-500 Roentgens per hour. The sliding cover on the bottom of the meter case blocks Beta particles when closed allowing only Gamma radiation to pass through the detector. When the cover is opened this allows Beta particles to pass through the very thin metal membrane on the bottom of the CD V-720's Ion Chamber resulting in detection of beta radiation. See picture below.
In the above image the holes on the bottom of the Ion Chamber can be seen. The bottom of the CD V-720 Ion Chamber has a thinner metal (.006 inch) on the bottom. This thin material allows the Beta particles to pass through the thinner metal bottom and then be detected by the chamber. The Victoreen CD-V720 Model 3A (seen here) has a thick aluminum plate with holes glued to the bottom of the chamber to reinforce it around the thin area and for protection.
Inside of the Chatham CD V-720. Click photo to see larger.
As far as I know Chatham only made a CD V-720 and CD V-700 in the early days. These Chatham meters are really unique. Note the plastic strap battery holders and the rounded, cast case design. This meter has the sliding metal cover on the bottom like all 720s. Also worth noting is that the ion chamber is mounted inside the removable bottom of the meter and has a cable that plugs into the top electronics section when the bottom is installed.