The Fluke 845 does not use a mercury cell. In a lot of these type systems, the mercury cell was used in a ratiometric configuration. Its exact voltage is not important. What is important is a stable voltage over your measurement interval. Lithium cells are usually OK. Also the NE-2 neon lamps are still made, readily available, and dirt cheap. Standard chicken soup for a twitchy 845 is to clean all the switch contacts, check the electrolytics, check the chopper system. _________________________________________________________________ Hotmail: Trusted email with powerful SPAM protection. http://clk.atdmt.com/GBL/go/210850553/direct/01/

I attempted to head off chopper failure by replacing my 740B's neon lamps with NE2H's (NE-2H was recommended by HP tech at now defunct Paramus,NJ repair center) from Digikey (about 1993). Worked for about an hour. Tried another set of lamps, choppers still dead. I wasn't in the mode to troubleshoot, and figured I'll pre-age the rest of my stock for 24 hours in a string of relaxation oscillators. No go. Replaced with the original HP NE2 style lamps, and no trouble since. From what I've read (Signalite catalog from around 1972), there was a difference between illumination NE2's, and control NE2's. Some differences would be due to lack of radioacitve gas in illumination neons, as these wouldn't be subject to total darkness, as is the case in a chopper. Without radioactivity, NE2's suffer from "dark effect" with reduced light output. Also, it is better to have a lamp without emissive coatings on the electrodes. While coatings are good for constant illumination, they're bad for stability. Perhaps my stock of lamps was more prone to sputtering, which also would darken them. All China sourced NE2 lamps I've come across, are strictly optimized for illumination. No one produces "control neons" anymore. Perhaps generic NE2's (NE-2H's) from 40 years ago just happened to be stable enough, and bright enough, to permit that HP tech to use them to replace factory lamps. If anyone on this list has had recent, long term success, replacing the neon lamps in HP419's, or HP740B's, please post the source for your lamps. Stan On Thu, Mar 25, 2010 at 7:20 PM, Mark Sims <holrum@hotmail.com> wrote: > > The Fluke 845 does not use a mercury cell. > > In a lot of these type systems, the mercury cell was used in a ratiometric > configuration. Its exact voltage is not important. What is important is a > stable voltage over your measurement interval. Lithium cells are usually > OK. > > Also the NE-2 neon lamps are still made, readily available, and dirt > cheap. > > Standard chicken soup for a twitchy 845 is to clean all the switch > contacts, check the electrolytics, check the chopper system. > > > > _________________________________________________________________ > Hotmail: Trusted email with powerful SPAM protection. > http://clk.atdmt.com/GBL/go/210850553/direct/01/ > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

Two different neons with the same part number seems very unlikely. More likely is a change in production over time eliminating the radioactive component. In a hotel bathroom, I saw a wall-mounted hair dryer with a neon pilot light. If the room was dark, the neon was out. If you turned on the room lights, the pilot glowed. A flashlight would also make the neon glow. -John ============= > I attempted to head off chopper failure by replacing my 740B's neon lamps > with NE2H's (NE-2H was recommended by HP tech at now defunct Paramus,NJ > repair center) from Digikey (about 1993). Worked for about an hour. Tried > another set of lamps, choppers still dead. I wasn't in the mode to > troubleshoot, and figured I'll pre-age the rest of my stock for 24 hours > in > a string of relaxation oscillators. No go. Replaced with the original HP > NE2 > style lamps, and no trouble since. From what I've read (Signalite catalog > from around 1972), there was a difference between illumination NE2's, and > control NE2's. Some differences would be due to lack of radioacitve gas in > illumination neons, as these wouldn't be subject to total darkness, as is > the case in a chopper. Without radioactivity, NE2's suffer from "dark > effect" with reduced light output. Also, it is better to have a lamp > without > emissive coatings on the electrodes. While coatings are good for constant > illumination, they're bad for stability. Perhaps my stock of lamps was > more > prone to sputtering, which also would darken them. All China sourced NE2 > lamps I've come across, are strictly optimized for illumination. No one > produces "control neons" anymore. Perhaps generic NE2's (NE-2H's) from 40 > years ago just happened to be stable enough, and bright enough, to permit > that HP tech to use them to replace factory lamps. > > If anyone on this list has had recent, long term success, replacing the > neon > lamps in HP419's, or HP740B's, please post the source for your lamps. > > Stan > > On Thu, Mar 25, 2010 at 7:20 PM, Mark Sims <holrum@hotmail.com> wrote: > >> >> The Fluke 845 does not use a mercury cell. >> >> In a lot of these type systems, the mercury cell was used in a >> ratiometric >> configuration. Its exact voltage is not important. What is important >> is a >> stable voltage over your measurement interval. Lithium cells are >> usually >> OK. >> >> Also the NE-2 neon lamps are still made, readily available, and dirt >> cheap. >> >> Standard chicken soup for a twitchy 845 is to clean all the switch >> contacts, check the electrolytics, check the chopper system. >> >> >> >> _________________________________________________________________ >> Hotmail: Trusted email with powerful SPAM protection. >> http://clk.atdmt.com/GBL/go/210850553/direct/01/ >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > >

Hi,NE-2 is now  a very generic number. Lots of variation in detail design and materials. Many discharge lamps and devices use radioactive isotopes to maintain a low level of ionisation. Krypton 85 was commonly used in the gas mix. It has a half life of 10 years, it's decay may be a factor in lamp failure. Tritium is used in modern devices. Nickel 63 or Cobalt 60 can be used in the electrodes (normally only one to save cost) and sometimes Radium 226 was used in older devices (I have a 1B29 T/R tube that is quite hot). Often the choice of isotope was down to what was cheapest at the time. Note that at low voltages some LEDs  won't work in the dark either! To use an LED in place of  a neon (AC) just use two back to back. CDS cells peak around 520nm so a high efficiency green LED (LMP-LM65 to keep it in the family) would be a good choice at 525nm.Robert G8RPI. P.S. I'm a Geiger Counter Enthusiast as well as a time and Volt nut, whole different set of measurement issues! --- On Fri, 26/3/10, J. Forster <jfor@quik.com> wrote: From: J. Forster <jfor@quik.com> Subject: Re: [volt-nuts] HP 419 & Fluke 845 To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Date: Friday, 26 March, 2010, 3:11 Two different neons with the same part number seems very unlikely. More likely is a change in production over time eliminating the radioactive component. In a hotel bathroom, I saw a wall-mounted hair dryer with a neon pilot light. If the room was dark, the neon was out. If you turned on the room lights, the pilot glowed. A flashlight would also make the neon glow. -John ============= > I attempted to head off chopper failure by replacing my 740B's neon lamps > with NE2H's (NE-2H was recommended by HP tech at now defunct Paramus,NJ > repair center) from Digikey (about 1993). Worked for about an hour. Tried > another set of lamps, choppers  still dead. I wasn't in the mode to > troubleshoot, and figured I'll pre-age the rest of my stock for 24 hours > in > a string of relaxation oscillators. No go. Replaced with the original HP > NE2 > style lamps, and no trouble since. From what I've read (Signalite catalog > from  around 1972), there was a difference between illumination NE2's, and > control NE2's. Some differences would be due to lack of radioacitve gas in > illumination neons, as these wouldn't be subject to total darkness, as is > the case in a chopper. Without radioactivity, NE2's suffer from "dark > effect" with reduced light output. Also, it is better to have a lamp > without > emissive coatings on the electrodes. While coatings are good for constant > illumination, they're bad for stability. Perhaps my stock of lamps was > more > prone to sputtering, which also would darken them. All China sourced NE2 > lamps I've come across, are strictly optimized for illumination. No one > produces "control neons" anymore. Perhaps generic NE2's (NE-2H's) from 40 > years ago just happened to be stable enough, and bright enough, to permit > that HP tech to use them to replace factory lamps. > > If anyone on this list has had recent, long term success, replacing the > neon > lamps in HP419's, or HP740B's, please post the source for your lamps. > > Stan > > On Thu, Mar 25, 2010 at 7:20 PM, Mark Sims <holrum@hotmail.com> wrote: > >> >> The Fluke 845 does not use a mercury cell. >> >> In a lot of these type systems,  the mercury cell was used in a >> ratiometric >> configuration.  Its exact voltage is not important.   What is important >> is a >> stable voltage over your measurement interval.   Lithium cells are >> usually >> OK. >> >> Also the NE-2 neon lamps are still made,  readily available,  and dirt >> cheap. >> >> Standard chicken soup for a twitchy 845 is to clean all the switch >> contacts,   check the electrolytics,  check the chopper system. >> >> >> >> _________________________________________________________________ >> Hotmail: Trusted email with powerful SPAM protection. >> http://clk.atdmt.com/GBL/go/210850553/direct/01/ >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

I vaguely remember reading that the time response (on to off time) of CdS cells varied with input wavelength of the light, but can't currently find a reference. It was in a paper I read in the late 60s, I think. -John ============ > Hi,NE-2 is now  a very generic number. Lots of variation in detail design > and materials. Many discharge lamps and devices use radioactive isotopes > to maintain a low level of ionisation. Krypton 85 was commonly used in the > gas mix. It has a half life of 10 years, it's decay may be a factor in > lamp failure. Tritium is used in modern devices. Nickel 63 or Cobalt 60 > can be used in the electrodes (normally only one to save cost) and > sometimes Radium 226 was used in older devices (I have a 1B29 T/R tube > that is quite hot). Often the choice of isotope was down to what was > cheapest at the time. Note that at low voltages some LEDs  won't work in > the dark either! To use an LED in place of  a neon (AC) just use two back > to back. CDS cells peak around 520nm so a high efficiency green LED > (LMP-LM65 to keep it in the family) would be a good choice at 525nm.Robert > G8RPI. > P.S. I'm a Geiger Counter Enthusiast as well as a time and Volt nut, whole > different set of measurement issues! > > --- On Fri, 26/3/10, J. Forster <jfor@quik.com> wrote: > > From: J. Forster <jfor@quik.com> > Subject: Re: [volt-nuts] HP 419 & Fluke 845 > To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> > Date: Friday, 26 March, 2010, 3:11 > > Two different neons with the same part number seems very unlikely. More > likely is a change in production over time eliminating the radioactive > component. > > In a hotel bathroom, I saw a wall-mounted hair dryer with a neon pilot > light. > > If the room was dark, the neon was out. > If you turned on the room lights, the pilot glowed. > A flashlight would also make the neon glow. > > -John > > ============= > > > > >> I attempted to head off chopper failure by replacing my 740B's neon >> lamps >> with NE2H's (NE-2H was recommended by HP tech at now defunct Paramus,NJ >> repair center) from Digikey (about 1993). Worked for about an hour. >> Tried >> another set of lamps, choppers  still dead. I wasn't in the mode to >> troubleshoot, and figured I'll pre-age the rest of my stock for 24 hours >> in >> a string of relaxation oscillators. No go. Replaced with the original HP >> NE2 >> style lamps, and no trouble since. From what I've read (Signalite >> catalog >> from  around 1972), there was a difference between illumination NE2's, >> and >> control NE2's. Some differences would be due to lack of radioacitve gas >> in >> illumination neons, as these wouldn't be subject to total darkness, as >> is >> the case in a chopper. Without radioactivity, NE2's suffer from "dark >> effect" with reduced light output. Also, it is better to have a lamp >> without >> emissive coatings on the electrodes. While coatings are good for >> constant >> illumination, they're bad for stability. Perhaps my stock of lamps was >> more >> prone to sputtering, which also would darken them. All China sourced NE2 >> lamps I've come across, are strictly optimized for illumination. No one >> produces "control neons" anymore. Perhaps generic NE2's (NE-2H's) from >> 40 >> years ago just happened to be stable enough, and bright enough, to >> permit >> that HP tech to use them to replace factory lamps. >> >> If anyone on this list has had recent, long term success, replacing the >> neon >> lamps in HP419's, or HP740B's, please post the source for your lamps. >> >> Stan >> >> On Thu, Mar 25, 2010 at 7:20 PM, Mark Sims <holrum@hotmail.com> wrote: >> >>> >>> The Fluke 845 does not use a mercury cell. >>> >>> In a lot of these type systems,  the mercury cell was used in a >>> ratiometric >>> configuration.  Its exact voltage is not important.   What is important >>> is a >>> stable voltage over your measurement interval.   Lithium cells are >>> usually >>> OK. >>> >>> Also the NE-2 neon lamps are still made,  readily available,  and dirt >>> cheap. >>> >>> Standard chicken soup for a twitchy 845 is to clean all the switch >>> contacts,   check the electrolytics,  check the chopper system. >>> >>> >>> >>> _________________________________________________________________ >>> Hotmail: Trusted email with powerful SPAM protection. >>> http://clk.atdmt.com/GBL/go/210850553/direct/01/ >>> _______________________________________________ >>> volt-nuts mailing list -- volt-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >>> and follow the instructions there. >>> >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. >> >> > > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > > >