[volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

[Pete Lancashire]

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 at 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 at febo.com] On Behalf Of Pete
> Lancashire
> Sent: 16 November 2017 18:24
> To: Discussion of precise voltage measurement
> Cc: hp_agilent_equipment at 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 at 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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