--- In CDV700CLUB@yahoogroups.com, "Ron" <telewinze@a...> wrote:
> Why not this "surplus" tube as a spare? Whats the ups and downs?
>
> PROBE 5980 THESE PROBES WERE USED IN THE SEVERAL MILITARY COUNTERS
TO
> EXTEND THE RANGE UP TO 500mR/hr. EASILY ADAPTABLE TO THE CDV-700
FOR
> RANGE EXTENSION.
>
> It's about $30 plus shipping.
>
>
The QPL 5980 is a small thin wall tube for Gamma detection only. A
modern part number would be LND 726.
They both return 3.5 CPS per 1 mR/H. Used as the high range tube in
many wide dynamic range Military Geiger's.

3.5 CPS = 210 CPM, therefore with a CDV700, max reading would be
30,000 ( max range switch) / 210 =142 mR/H.

A LENi with X2 range extender switch would double that.

Clearly the CDV-700 based units are biased for very low,
environmental and science project ranges.

Ludlum Model 3 has a 0-500,000 CPM range, so could read out all the
way to 2380 mR/H ( 2.38R/H)
still not WAR METER material, but better than the original Military
capabilities ( .5 R/H)

Most of the commercial high range tubes use 500V, while the Military
versions all use 700V. CDV-700's use 900V and are not normally
adjustable.

This is not a deal breaker though, because I have developed an in-
probe adaptor that works very well:
From the meter jack, series a 3.3M resistor with a 1.8M resistor,
then run that to the tube. At the junction of the two resistors,
place a Zener Diode string to ground, of a value to equal the tube's
requirement ( say 700V). Now from the connection point on the tube,
run a .01 uF, 2000V capacitor back to the jack connection. The
resistors and Zeners drop the 900V down to that required by the tube,
while the capacitor shunts that DC network, passing the pulse back to
the meter.

In most meters, this setup works perfectly, and is the basis for a
new probe I'm making, using those 480V Russian Pancakes!

One last thing, Lee Frank now advertises the 5980's for 19.99 USD on:

http://www.surplustuff.com/radiolog.html

Note, his 7616 is also small and has 10 CPS per 1 mR/H.

Have Fun

Geo