Would you guys slow down long enough for me to type a reply? ?:)
Tom,?Dave,
I wish. ?But the glass stops beta. ?The Kr-85 worked?because it was?inside.
Bob, Elliott,
So many parts in series... sometimes brute force is the best solution, but this one puts me off. ?That's just my personal taste; if you want to do
it, knock yourself out.
Elliott,
HP used?1% metal film resistors. ?The pot is a weak point for long-term stability, but I think that since it's in a voltage divider the high-leg tempco compensates the low-leg tempco.
In a related thread, Alan Melia suggests adding a LED to illuminate the gas tube. ?If the problem was dark effect, brought on by Kr-85 depletion, that should work around it just
dandy. ?I hope someone tries it. ?I can't, my ZZ1000 is still working. ?If I can find a flickering neon at home, I'll try to figure out what wavelength LED is the most effective. ?It will be visible light, not?UV, the glass blocks UV, same as external nuclear?radiation.
Dave Wise?
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From: hp_agilent_equipment@... <hp_agilent_equipment@...> on behalf of Tom Gardner tggzzz@... [hp_agilent_equipment]
<hp_agilent_equipment@...>
Sent: Friday, July 14, 2017 2:18 PM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?
?
Or to a supermarket and find the "LoSalt". Replacing part of the NaCl with KCl inevitably includes K40 :)
On 14/07/17 22:15, Artek Manuals
manuals@... [hp_agilent_equipment] wrote:
?
Go down to one of those 2nd hand store with your geiger counter and find a very old $5 watch with the glow in the dark? radium painted hands and dial. Peel of the minute hand and shrink tube it to the NE-2
:-)
Dave
manuals@...
On 7/14/2017 5:06 PM, 'Alan Melia'
Alan.Melia@... [hp_agilent_equipment] wrote:
?
?
The thing is that most "zeners" do not depend on the Zener effect. That only occurs around voltages up to around 4volts, above 5v the process is Avalanche Breakdown , a bit like a gas tube. Then the temperature coefficient of
these two processes have opposite senses so if you combine a true?Zener with a forward diode or an avalanche diode you can minimise the tempco.?The lowest tempcos are usually around 5 to 6v."zeners".
?
Alan
G3NYK
----- Original Message -----
Sent: Friday, July 14, 2017 9:16 PM
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?
Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.
When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the
voltage.
There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.
Let us know your re sults.
Bob
Hi Dave,
In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.
However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and
remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?
Thanks all for your input!
--E
W6EL
?
--
Dave
Manuals@...
