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Can anyone help with info on this great find ??

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sparky99

Mon Jul 12 2010, 12:45AM

Registered Member #1159 Joined: Fri Dec 07 2007, 02:10AM
Location: Hudson Valley of NY State
Posts: 84

Hi All,
Was at a Hamfest in Sussex, NJ today and found a Jennings J 1003 high voltage voltmeter at a price I couldn't pass up. Just looks alone was well worth the price! I had 4 offers to buy it, one for 8 times what I paid for it, but turned them down. I sure would like to have a manual for it, but there is little online.

Anyone have any info on this gem. A search of Jennings website turns up nothing.

Thanks,
bob

radiotech

Mon Jul 12 2010, 02:49AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Try here

It looks like a nice pre-digital meter for testing the things Jennings makes

Patrick

Mon Jul 12 2010, 04:47AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

how does that thing work?

Herr Zapp

Mon Jul 12 2010, 06:20AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Sparky -

Nice find ....... it's a Jennings Technology J-1000 capacitive voltage divider. I believe the ratio is 1,000:1.

Take care to protect the glass vacuum capacitors; if I remember correctly they just plug in to the housing from the top. I'd keep the capacitors in separate well-protected packaging except when actually using the instrument.

These dividers show up on eBay from time to time, frequently missing one (or both) of the capacitors.

Regards,
Herr Zapp

Patrick

Mon Jul 12 2010, 09:13AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

did i see on the pic a 100kv range?!

you wanna sell it to me?

does it have a frequency capability? or is it just a near DC affair?

IntraWinding

Mon Jul 12 2010, 11:11AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

What a great meter! I'm envious!

I'm under the impression that a vacuum capacitor operated at 100KV would be an X-Ray hazard, but the meter design seems to suggest the manufacturer didn't see this as a concern.
Either that or the manual warns you to only read the meter from a good distance with binoculars!

So does anyone know the truth about vacuum capacitors and X-Rays?

Proud Mary

Mon Jul 12 2010, 01:25PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

What a great meter! I'm envious!

I'm under the impression that a vacuum capacitor operated at 100KV would be an X-Ray hazard, but the meter design seems to suggest the manufacturer didn't see this as a concern.
Either that or the manual warns you to only read the meter from a good distance with binoculars!

So does anyone know the truth about vacuum capacitors and X-Rays?

The Jennings instrument is an antique, and dates to a period of minimalist radiological protection standards.

Any vacuum capacitor with a pd across it sufficient to produce electron field emission tunneling will generate X-rays - but only when ~10-15kV is applied will these
X-ray photons have sufficient energy to transit the glass envelope.

There is no fundamental difference between a cold cathode X-ray tube and a vacuum capacitor, except the geometry of the electrodes.

IntraWinding

Mon Jul 12 2010, 02:21PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

sparky99:
OK, so you need to be aware of an X-Ray hazard when this meter is used!

Proud Mary:
I'm wondering about ways to minimise the X-Ray hazard from a vacuum capacitor.
Clearly having one electrode physically located within the other allows the outer electrode material to act as an X-Ray shield.
On that basis a more substantial outer electrode made of a more X-Ray opaque material would be advantageous.
Are some electrode materials less efficient producers of the more hazardous X-Rays.
Would larger radius electrode surfaces reduce electron emission?
What about having the electrodes coated in an insulating layer?

Proud Mary

Mon Jul 12 2010, 02:59PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

IntraWinding wrote ...

[Proud Mary:
I'm wondering about ways to minimise the X-Ray hazard from a vacuum capacitor.
Clearly having one electrode physically located within the other allows the outer electrode material to act as an X-Ray shield.
On that basis a more substantial outer electrode made of a more X-Ray opaque material would be advantageous.
Are some electrode materials less efficient producers of the more hazardous X-Rays.
Would larger radius electrode surfaces reduce electron emission?
What about having the electrodes coated in an insulating layer?

I know very little about vacuum capacitors, but would imagine that they are subject to some of the same constraints as thermionic valves when it comes to choice of construction materials - compatible metal-to-glass seals, compatible coefficients of thermal expansion and contact potential problems between dissimilar metals, gas absorption and adsorption by the electrodes, and so on.

In thermionic valve technology, unwanted X-ray emission was often dealt with by the use of lead glass, warnings printed on the glass bulb, and hazard information in the data sheet. A good example of this was the American TV shunt stabiliser triode 6BK4. In its first two iterations, 6BK4A and 6BKB, this interesting valve came with a standard high temperature glass mix, but after the TV X-ray scare of the late 1960s, the 6BK4C became obviously heavier than its predecessors due to the use of lead glass, and it now sported a printed warning on the bulb, and in the data sheet. The manufacturers did not see lead glass alone as sufficient to attenuate the X-rays, so the user was advised to operate the valve inside a metal enclosure to reduce the domestic viewer's justified paranoia to non-litigious proportions.

TV thermionic EHT rectifiers could also become a hazardous source of X-rays when their heaters failed. In normal operation, the forward voltage drop across the valve would be a few hundred volts, but when the heater failed, the PD across the valve would jump to 30kV or so, making it a potent source of X-rays.

Today, vacuum capacitors have few applications outside of high power transmitters, whose designers could be expected to manage the X-ray hazard as part of their overall safety brief. Unwanted X-ray production is not confined to vacuum capacitors, but is always a problem to be worked around with high power RF amplifier valves having tens of kV of anode voltage.

See:

X-ray emission from broadcast transmitters

Hunter, E.B.
Voice of America, Greenville, NC

This paper appears in: Broadcasting, IEEE Transactions on
Issue Date: Mar 1990
Volume: 36 Issue: 1
On page(s): 14 - 23
ISSN: 0018-9316
INSPEC Accession Number: 3689360
Digital Object Identifier: 10.1109/11.52360
Date of Current Version: 06 August 2002

ABSTRACT

During the past few years amplitude-modulated transmitters employing efficient pulse-width modulators have come into common use. These transmitters are reliable, relatively insensitive to vacuum tube characteristics, and offer excellent audio fidelity. Their architecture requires, however, supply voltages in the 20-30-kV range, which greatly enhances the production of ionizing radiation in the form of X-rays. Recent analysis by Voice of America indicates that these X-rays are being emitted in short, high-intensity bursts focused into broad radial beams. The general aspects of ionizing radiation of interest to communications engineers are reviewed. The spectral and time-domain characteristics of X-ray radiation from transmitters are examined, a method for estimating fault-condition radiation values is suggested, and the findings of the Voice of America are discussed

quicksilver

Mon Jul 12 2010, 07:32PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Perhaps it would be advisable to build a cover of some transparent type to both protect you and the tubes....?

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