Neon bulbs for HP 3420B or 419A chopper circuit
In an earlier post I quoted the following description of the photo-chopper
circuit from the 419A manual
4-43. Assume that DS1 lights when the input is applied to T2. Capacitor
C1 charges until the oscillator switches the input, and DS1 goes off. When
the oscillator switches again, the charge on C1 insures that DS2 fires, and
DS1 stays off. This cycle continues with DS1 and DS2 firing as long as
there is output from the oscillator. CR1 and CR2 prevent the capacitor from
discharging through R1 and R2
That description also applies to the 3420B chopper.
For this to work as described, George Einst says that the striking
characteristics on the neons are critical, which I totally believe given
what's happening in mine.
AFAICT, both neons are striking on every +ve portion of the square wave
drive signal, so the flip-flop behaviour doesn't happen.
I checked on the curve tracer, and both neons strike at almost exactly 70V.
Both are also totally clear which suggests to me that they are not the
originals.
Does anyone have any idea how much the strike voltages would need to differ
for this to work, and does anyone have any suitable neons - the only ones I
have are these shorter ones and they strike at about 125V.
These are the longer bodied neons (glass about 5/8" long).
Thank you
Dave Partridge
I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V
http://www.farnell.com/datasheets/57560.pdf
-pete
On Thu, Nov 16, 2017 at 6:38 AM, David C. Partridge <
david.partridge@perdrix.co.uk> wrote:
In an earlier post I quoted the following description of the photo-chopper
circuit from the 419A manual
4-43. Assume that DS1 lights when the input is applied to T2. Capacitor
C1 charges until the oscillator switches the input, and DS1 goes off.
When
the oscillator switches again, the charge on C1 insures that DS2 fires, and
DS1 stays off. This cycle continues with DS1 and DS2 firing as long as
there is output from the oscillator. CR1 and CR2 prevent the capacitor
from
discharging through R1 and R2
That description also applies to the 3420B chopper.
For this to work as described, George Einst says that the striking
characteristics on the neons are critical, which I totally believe given
what's happening in mine.
AFAICT, both neons are striking on every +ve portion of the square wave
drive signal, so the flip-flop behaviour doesn't happen.
I checked on the curve tracer, and both neons strike at almost exactly 70V.
Both are also totally clear which suggests to me that they are not the
originals.
Does anyone have any idea how much the strike voltages would need to differ
for this to work, and does anyone have any suitable neons - the only ones I
have are these shorter ones and they strike at about 125V.
These are the longer bodied neons (glass about 5/8" long).
Thank you
Dave Partridge
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To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/volt-nuts
and follow the instructions there.
Errm - I'm looking for around 65-75V range so I end up near but not exactly the same as the 70V ones that are already there.
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Pete Lancashire
Sent: 16 November 2017 18:24
To: Discussion of precise voltage measurement
Cc: hp_agilent_equipment@yahoogroups.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit
I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V
http://www.farnell.com/datasheets/57560.pdf
-pete
On Thu, Nov 16, 2017 at 6:38 AM, David C. Partridge < david.partridge@perdrix.co.uk> wrote:
In an earlier post I quoted the following description of the
photo-chopper circuit from the 419A manual
4-43. Assume that DS1 lights when the input is applied to T2. Capacitor
C1 charges until the oscillator switches the input, and DS1 goes off.
When
the oscillator switches again, the charge on C1 insures that DS2 fires, and
DS1 stays off. This cycle continues with DS1 and DS2 firing as long as
there is output from the oscillator. CR1 and CR2 prevent the
capacitor from discharging through R1 and R2
That description also applies to the 3420B chopper.
For this to work as described, George Einst says that the striking
characteristics on the neons are critical, which I totally believe
given what's happening in mine.
AFAICT, both neons are striking on every +ve portion of the square
wave drive signal, so the flip-flop behaviour doesn't happen.
I checked on the curve tracer, and both neons strike at almost exactly 70V.
Both are also totally clear which suggests to me that they are not the
originals.
Does anyone have any idea how much the strike voltages would need to
differ for this to work, and does anyone have any suitable neons - the
only ones I have are these shorter ones and they strike at about 125V.
These are the longer bodied neons (glass about 5/8" long).
Thank you
Dave Partridge
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.
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and follow the instructions there.
sorry got it upside down must have been lost in the translation :-)
so you need some 'good old' NE's. If you can find some in the UK/EU I can
send you a few.
-pete
On Thu, Nov 16, 2017 at 1:08 PM, David C. Partridge <
david.partridge@perdrix.co.uk> wrote:
Errm - I'm looking for around 65-75V range so I end up near but not
exactly the same as the 70V ones that are already there.
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Pete
Lancashire
Sent: 16 November 2017 18:24
To: Discussion of precise voltage measurement
Cc: hp_agilent_equipment@yahoogroups.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit
I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V
http://www.farnell.com/datasheets/57560.pdf
-pete
On Thu, Nov 16, 2017 at 6:38 AM, David C. Partridge <
david.partridge@perdrix.co.uk> wrote:
In an earlier post I quoted the following description of the
photo-chopper circuit from the 419A manual
4-43. Assume that DS1 lights when the input is applied to T2.
Capacitor
C1 charges until the oscillator switches the input, and DS1 goes off.
When
the oscillator switches again, the charge on C1 insures that DS2 fires,
and
DS1 stays off. This cycle continues with DS1 and DS2 firing as long as
there is output from the oscillator. CR1 and CR2 prevent the
capacitor from discharging through R1 and R2
That description also applies to the 3420B chopper.
For this to work as described, George Einst says that the striking
characteristics on the neons are critical, which I totally believe
given what's happening in mine.
AFAICT, both neons are striking on every +ve portion of the square
wave drive signal, so the flip-flop behaviour doesn't happen.
I checked on the curve tracer, and both neons strike at almost exactly
70V.
Both are also totally clear which suggests to me that they are not the
originals.
Does anyone have any idea how much the strike voltages would need to
differ for this to work, and does anyone have any suitable neons - the
only ones I have are these shorter ones and they strike at about 125V.
These are the longer bodied neons (glass about 5/8" long).
Thank you
Dave Partridge
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.
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Pete wrote:
I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V
Neon gas at the typical pressures used in small lamps ignites somewhere
near 200vDC. For this reason, commercial neon bulbs use a mixture of
Neon and Argon, which lowers the strike voltage to the 70-100v region
(again, depending on pressure). By this means, the original NE-2 was
designed to strike at around 70v (DC or peak AC), while the NE-2H was
designed to strike at around 120v (DC or peak AC).
BUT: You never know what the heck you might get from many sources
today. If you need a controlled strike voltage, the best bet is to buy
NEW bulbs from a reputable manufacturer who provides specs. Most such
bulbs have designations other than "NE-", although some are also
identified with an original type on the datasheet.
Note also that common neon lamps (e.g., NE-2) depend on some ambient
light to promote ionization due to the "dark effect." This is
particularly true for striking (many neons will not strike at all in
total darkness), but affects continuing operation as well. For this
reason, some variants had radioactive material added inside the envelope
to promote ionization. These were often identified as "dark effect
reduced" bulbs. The NE-2U, NE-2J, and NE-2H5 were among these.
Originally, Thorium was used for this purpose, but before long Krypton
85 became the standard additive. Being a gas, it was much easier to
incorporate. NOTE that the half-life of 85Kr is less than 11 years.
This explains most failures of neons in chopper and LDR applications today.
Radioactive enhancement is very important for chopper operation, since
the chopper assembly necessarily keeps the lamps in total darkness. It
also means that you probably do not want to buy/use surplus neon bulbs
to repair choppers and LDRs (for two reasons -- you never know if they
really had radioactive enhancement to begin with, and if they are old
enough that you can be sure, they were made at least two half-lives ago
and probably more like four, so they are all pooped out before you even
install them).
I managed to source some brand-new NE-2U equivalents in small quantities
a few years ago, but I can't remember where I got them. (No problem if
you want 10k of them -- several manufacturers will be happy to oblige.)
Whatever you get, test them with a beta-sensitive detector to make sure
they are reasonably active. The indication should be unmistakably
strong -- if it's a case of, "Well, I think there may be some
indication," they will not do.
Best regards,
Charles
to buy NEW bulbs from a reputable manufacturer who provides specs
Any recommendations - I can't find a source in UK. I know Philips used to make them, but where I'd buy a few &deity only knows.
Thanks
Dave
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Charles Steinmetz
Sent: 17 November 2017 08:12
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit
Pete wrote:
I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V
Neon gas at the typical pressures used in small lamps ignites somewhere near 200vDC. For this reason, commercial neon bulbs use a mixture of Neon and Argon, which lowers the strike voltage to the 70-100v region (again, depending on pressure). By this means, the original NE-2 was designed to strike at around 70v (DC or peak AC), while the NE-2H was designed to strike at around 120v (DC or peak AC).
BUT: You never know what the heck you might get from many sources today. If you need a controlled strike voltage, the best bet is to buy NEW bulbs from a reputable manufacturer who provides specs. Most such bulbs have designations other than "NE-", although some are also identified with an original type on the datasheet.
Note also that common neon lamps (e.g., NE-2) depend on some ambient light to promote ionization due to the "dark effect." This is particularly true for striking (many neons will not strike at all in total darkness), but affects continuing operation as well. For this reason, some variants had radioactive material added inside the envelope to promote ionization. These were often identified as "dark effect reduced" bulbs. The NE-2U, NE-2J, and NE-2H5 were among these.
Originally, Thorium was used for this purpose, but before long Krypton
85 became the standard additive. Being a gas, it was much easier to incorporate. NOTE that the half-life of 85Kr is less than 11 years.
This explains most failures of neons in chopper and LDR applications today.
Radioactive enhancement is very important for chopper operation, since the chopper assembly necessarily keeps the lamps in total darkness. It also means that you probably do not want to buy/use surplus neon bulbs to repair choppers and LDRs (for two reasons -- you never know if they really had radioactive enhancement to begin with, and if they are old enough that you can be sure, they were made at least two half-lives ago and probably more like four, so they are all pooped out before you even install them).
I managed to source some brand-new NE-2U equivalents in small quantities a few years ago, but I can't remember where I got them. (No problem if you want 10k of them -- several manufacturers will be happy to oblige.)
Whatever you get, test them with a beta-sensitive detector to make sure they are reasonably active. The indication should be unmistakably strong -- if it's a case of, "Well, I think there may be some indication," they will not do.
Best regards,
Charles
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.
David wrote:
to buy NEW bulbs from a reputable manufacturer who provides specs
Any recommendations - I can't find a source in UK. I know Philips used to make them, but where I'd buy a few &deity only knows.
Google is your friend. neon, bulb, lamp, radioactive, and "dark effect"
are good search terms. Here's what I found in about 5 minutes (all
US-centric):
Mouser and Digi-Key both have quite a variety of neon bulbs available,
including bulbs with wire leads from VCC, JKL, and Lumex. You would
need to review datasheets and contact the manufacturers to inquire about
radioactive additives:
https://www.mouser.com/Optoelectronics/Lamps-Holders/Lamps/_/N-5g6r?Keyword=neon&FS=True\
Other large distributors probably have similar selections.
This catalog from VCClite indicates that some of their bulbs have
reduced dark effect, including the A1D-T and A2B, both of which Mouser
and Digi-Key carry:
https://vcclite.com/wp-content/uploads/wpallimport/files/files/NeonIndicatorLamps.pdf
You will probably still want to find out for sure if the dark effect
reduction is due to a radioactive additive.
Here's some general information on glow lamps:
25 pages of glow lamp specifications from GE back in the day. Quite a
few of them are listed as having a "mild radioactive additive" to reduce
the dark effect:
https://static1.squarespace.com/static/57ae25c75016e1690c41b053/t/57ae2fd003596ed24fa8f54c/1471033297306/Glow+Lamp+Specifications.pdf
The 1966 edition of the GE glow lamp manual can be found here:
http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/GE/General_Electric_Glow_Lamp_Datasheet_1966.pdf
Best regards,
Charles
Thank you, Charles, for the excellent summary and references.
Jeremy
N6WFO
On Fri, Nov 17, 2017 at 6:23 AM Charles Steinmetz csteinmetz@yandex.com
wrote:
David wrote:
to buy NEW bulbs from a reputable manufacturer who provides specs
Any recommendations - I can't find a source in UK. I know Philips used
to make them, but where I'd buy a few &deity only knows.
Google is your friend. neon, bulb, lamp, radioactive, and "dark effect"
are good search terms. Here's what I found in about 5 minutes (all
US-centric):
Mouser and Digi-Key both have quite a variety of neon bulbs available,
including bulbs with wire leads from VCC, JKL, and Lumex. You would
need to review datasheets and contact the manufacturers to inquire about
radioactive additives:
<
https://www.mouser.com/Optoelectronics/Lamps-Holders/Lamps/_/N-5g6r?Keyword=neon&FS=True
\
Other large distributors probably have similar selections.
This catalog from VCClite indicates that some of their bulbs have
reduced dark effect, including the A1D-T and A2B, both of which Mouser
and Digi-Key carry:
<
https://vcclite.com/wp-content/uploads/wpallimport/files/files/NeonIndicatorLamps.pdf
You will probably still want to find out for sure if the dark effect
reduction is due to a radioactive additive.
Here's some general information on glow lamps:
25 pages of glow lamp specifications from GE back in the day. Quite a
few of them are listed as having a "mild radioactive additive" to reduce
the dark effect:
<
https://static1.squarespace.com/static/57ae25c75016e1690c41b053/t/57ae2fd003596ed24fa8f54c/1471033297306/Glow+Lamp+Specifications.pdf
The 1966 edition of the GE glow lamp manual can be found here:
<
http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/GE/General_Electric_Glow_Lamp_Datasheet_1966.pdf
Best regards,
Charles
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