george wrote:

Note that the NE-2U is a "high brightness" lamp with a 135vDC (max)
strike voltage.  Standard brightness lamps strike at 90vDC (max).  The
Farnell site available to me here in the US lists the CML (Chicago
Miniature Lamp) A3C, which CML list with NE-2U as the "Old Reference
Number."

Farnell do not seem to carry the CML standard brightness lamps with
reduced dark effect.  According to the CML datasheet, there are four
part numbers with that combination:  A1D, A1D-T, A2B, and A2B-T.  "T"
indicates tinned leads.  The design current of the A1 parts is 300uA,
and of the A2 parts it is 700uA.  Check the schematic and you should be
able to calculate the neon operating current of the circuit, and choose
A1 or A2 accordingly.

Dave, perhaps Farnell will special order one of these part numbers for
you.  If Farnell can't get you the right part, I believe both Mouser and
Digi-Key operate in the UK and both have A1D(-T) and A2B(-T) parts in
stock (in the UK, I think).

Cheers,

Charles

Then an A3C (NE-2U) shouldn't work.  The drive voltage is 125V.

The operating current is 1.5mA (.15V/102R) in the 3420B, so I would expect this to be the A2B (NE-2V) part.

Interestingly the operating current for the 3420A is 2.45mA which you would think might suggest the A3C (NE-2U), but the drive voltage isn't high enough!

Dave

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Charles Steinmetz
Sent: 17 November 2017 20:53
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper

george wrote:

Note that the NE-2U is a "high brightness" lamp with a 135vDC (max) strike voltage.  Standard brightness lamps strike at 90vDC (max).  The Farnell site available to me here in the US lists the CML (Chicago Miniature Lamp) A3C, which CML list with NE-2U as the "Old Reference Number."

Farnell do not seem to carry the CML standard brightness lamps with reduced dark effect.  According to the CML datasheet, there are four part numbers with that combination:  A1D, A1D-T, A2B, and A2B-T.  "T"
indicates tinned leads.  The design current of the A1 parts is 300uA, and of the A2 parts it is 700uA.  Check the schematic and you should be able to calculate the neon operating current of the circuit, and choose
A1 or A2 accordingly.

Dave, perhaps Farnell will special order one of these part numbers for you.  If Farnell can't get you the right part, I believe both Mouser and Digi-Key operate in the UK and both have A1D(-T) and A2B(-T) parts in stock (in the UK, I think).

Cheers,

Charles

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and follow the instructions there.

David wrote:

Correct.

The NE-2V is another 700uA design current lamp, just like the CML A2B
and A2B-T.  Indeed, if you look at p.117 of the 1965 GE glow lamp manual
I linked to yesterday, you will see that it lists the NE-2V as an "A2B"
lamp, with "NE-2V" in parentheses.  So, the primary designation for this
lamp was "A2B" at least as far back as the mid-'60s.

Note that 700uA is the "design current," not the maximum safe current.
GE explicitly sanctioned using neon glow lamps at up to 2x the design
current, and they were routinely used at even higher currents back in
the day.  Some of GE's published application circuits used them at
2-3mA.  Mostly, the design current was the current at which the lifetime
was rated (higher current leads to shorter life).

It seems easy enough for you to obtain CML A2B or A2B-T lamps from
either Mouser or Digi-Key in the UK, so why don't you just get some and
see how they work?

I would not be surprised to find that the original neon lamps in the
3420A were 700uA "design current" parts that HP determined had
sufficient lifetime at the 3420A operating current.  If this is correct,
presumably the 3420A choppers fail with lower operating hours than the
419 and 3420B choppers.  (Perhaps this is why HP reduced the neon
currents in the "B" version?)

Note that 700uA was the highest "design current" rating for wire-leaded,
standard-brightness neons back in the day.

In a related vein, neon glow lamps produce less light as they age (both
from envelope darkening and because less of the cathode [DC operation]
is illuminated).  This may mean that the HP optical choppers degrade
significantly before they outright fail, so the chopper amps may start
drifting more than specified some time before the choppers fail entirely.

Best regards,

Charles

I'm in the process of getting some A2B neons from Mouser.

Dave

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of Charles Steinmetz
Sent: 18 November 2017 13:11
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper

David wrote:

Correct.

The NE-2V is another 700uA design current lamp, just like the CML A2B and A2B-T.  Indeed, if you look at p.117 of the 1965 GE glow lamp manual I linked to yesterday, you will see that it lists the NE-2V as an "A2B"
lamp, with "NE-2V" in parentheses.  So, the primary designation for this lamp was "A2B" at least as far back as the mid-'60s.

Note that 700uA is the "design current," not the maximum safe current.
GE explicitly sanctioned using neon glow lamps at up to 2x the design current, and they were routinely used at even higher currents back in the day.  Some of GE's published application circuits used them at 2-3mA.  Mostly, the design current was the current at which the lifetime was rated (higher current leads to shorter life).

It seems easy enough for you to obtain CML A2B or A2B-T lamps from either Mouser or Digi-Key in the UK, so why don't you just get some and see how they work?

I would not be surprised to find that the original neon lamps in the 3420A were 700uA "design current" parts that HP determined had sufficient lifetime at the 3420A operating current.  If this is correct, presumably the 3420A choppers fail with lower operating hours than the
419 and 3420B choppers.  (Perhaps this is why HP reduced the neon currents in the "B" version?)

Note that 700uA was the highest "design current" rating for wire-leaded, standard-brightness neons back in the day.

In a related vein, neon glow lamps produce less light as they age (both from envelope darkening and because less of the cathode [DC operation] is illuminated).  This may mean that the HP optical choppers degrade significantly before they outright fail, so the chopper amps may start drifting more than specified some time before the choppers fail entirely.

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.

Is there a relaible source for the GT-NE6H1925T neons?  Mouser has them for
special order and I suspect they want a high minimum quantity.  A source in
China lists them but I'm not sure I trust a Chinese source.

On Sat, Jan 6, 2018 at 8:19 AM, David C. Partridge <
david.partridge@perdrix.co.uk> wrote:

Randy,

There appears to be no MOQ on those bulbs and they have 972 in stock. I
think you can order what you want.

Todd

On Sat, Jan 6, 2018 at 12:34 PM, Randy Evans randyevans2688@gmail.com
wrote: