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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Jun 2019, 4:46 pm   #1
Wendymott
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Default Moving coil meter glass

Hi peeps....I bought a Pye base station TX with a meter that had a broken glass. Ok .. I thought... shouldnt be much of a problem..after an hour or so removing the glass residue from the front case... I made an acrylic replacement.
I was mindful of the possibility of static electricity and its effects.
However, the effects were too serious to "let go" and I decided that I should visit a glass emporium to cut a small piece . However...all my moving coil meter stock has acrylic covers or windows..... so how does that work ?? has meter acrylic some sort of anti static medium inserted into the mix ?? Over to you.
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Old 12th Jun 2019, 4:53 pm   #2
The Philpott
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Default Re: Moving coil meter glass

Also....do you notice that some plastic fronted meters are ribbed? - is this increase in surface area a dispersal strategy for static, and if so how does it work...? (Or is it just aesthetics to cover up the moving parts?)

I too used acrylic -once- and reverted to glass as found it unsatisfactory.

No answers, only more questions!

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Old 12th Jun 2019, 5:36 pm   #3
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Default Re: Moving coil meter glass

I have a swr bridge with a plastic meter the 0 setting changes if i clean with a microfiber cloth . The 0 goes anywhare from 0 to 3 or 4 i find a dry paintbrush flicked across plastic scale does the trick removing the static and restoring normality Mick
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Old 12th Jun 2019, 5:49 pm   #4
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Default Re: Moving coil meter glass

Other plastics are available.

Could they be using polystyrene, polycarbonate, etc?
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Old 12th Jun 2019, 8:18 pm   #5
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Default Re: Moving coil meter glass

I've had this problem with a few meters. Wiping with a damp cloth clears the static so now I only ever use a damp cloth for dust removal or cleaning purposes. It's surprising how long the static persists once you've used a dry duster.

Alan
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Old 12th Jun 2019, 8:20 pm   #6
Wendymott
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Default Re: Moving coil meter glass

I use the work !acrylic" as a catch all.. meaning clear plastic.. rather than perspex or other types...Yes Philpot...Some are ribbed, but I think thats a cheap way of keeping us "out" of the viewing gubbins, rather than static dispersal.. could be wrong.. but hey ho
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Old 12th Jun 2019, 8:34 pm   #7
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Default Re: Moving coil meter glass

A few weeks ago, I cleaned the plastic cover of a meter on an old Farnell PSU with a car polish, successfully making it a little more clear to see through. Immediately afterwards, I found that I had made the movement incredibly sensitive to static, but the effect completely disappeared over a day or so.

Try leaving your item in some warm water for a while, maybe it's an adsorption effect

B
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Old 12th Jun 2019, 10:44 pm   #8
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Default Re: Moving coil meter glass

You might not know that 2mm 'picture glass' will cut with a pair of scissors (!!), if you do it under water. No, I don't know why that stops it shattering, but it does. I cut rough circles out, and then use a belt linisher to abrade them into the true shape - it works very well. Sometimes I pick up broken picture frames on the street to keep the glass for such things.
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Old 13th Jun 2019, 9:00 am   #9
The Philpott
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Default Re: Moving coil meter glass

Underwater- it's possible that rather than simple lubrication, it's that the high speed destructive vibrations are damped before they can escalate to the breaking point of the work piece. (heavy water might be even better...!)

It's unfortunate that glass becomes completely invisible underwater, hence swimming pool rules.

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Old 13th Jun 2019, 12:20 pm   #10
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Default Re: Moving coil meter glass

Quote:
Originally Posted by The Philpott View Post
Underwater- it's possible that rather than simple lubrication, it's that the high speed destructive vibrations are damped before they can escalate to the breaking point of the work piece.e
Yes that's what I've read too a long time in one of those books with 150 experiments to do at home, so perhaps not the most scientific of sources.
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Old 13th Jun 2019, 1:47 pm   #11
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Default Re: Moving coil meter glass

Hi peeps... update.... Thanks for all the suggestions... I had a parallel thought re picture frame glass and located some old picture frames..unfortunately after umpteen efforts to cut to size.. I gave up and visited the local glass merchant who quickly cut a piece for 1. Result.
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Old 13th Jun 2019, 2:01 pm   #12
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Default Re: Moving coil meter glass

Old glass is hard to cut as it has a mass of scratches on it ready to take your proposed cut anywhere, new glass however, a joy to cut. Score, snap, done.
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Old 13th Jun 2019, 3:45 pm   #13
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Default Re: Moving coil meter glass

Static on plastic-cased meters can be dissipated using a quick burst of one of the various anti-static sprays available from RS etc.

And I remember an old Pat Hawker's TT in which it was suggested that wiping the front of a plastic meter with undiluted washing-up liquid on a tissue would work just as well.
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Old 13th Jun 2019, 4:29 pm   #14
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Default Re: Moving coil meter glass

The only glass cutter I ever use is one of these K-Star ones:

http://kansacraft.co.uk/stainedglass...&product_id=59

Use it like a pen by pushing forward, you can cut all shapes with ease, even re-entrant curves.
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Old 13th Jun 2019, 9:19 pm   #15
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Default Re: Moving coil meter glass

I always thought it was an Old Wives' Tale about cutting glass with scissors underwater. It seemed to me that if you cut yourself underwater, you could lose a lot of blood without knowing about it until it was too late. Normally I would be up for a bit of experimentation, but I was happy not knowing whether or not something was going to kill me, thank you very much!
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Old 14th Jun 2019, 5:20 pm   #16
Wendymott
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Default Re: Moving coil meter glass

I decided that to save loss of blood etc.. if glass is ok for Pye.. its ok for me.. but thanks everyone......As the meter has been rebuilt.. I will not try the various methods... till next time.73's all
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Old 16th Jun 2019, 12:03 pm   #17
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Default Re: Moving coil meter glass

Decades ago when I worked for Pye, the glass was available as a spare part.
I have used all those I had unfortunately.
Rob
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Old 16th Jun 2019, 3:15 pm   #18
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Default Re: Moving coil meter glass

Cutting glass under water. Since the glass in water is almost - if not entirely - invisible, try this trick.
Use an ink marker that is not water based - I use a Sasco Flip-Pad pen (red ink: may not be the most appropriate colour , but it's available here) - and mark the edges of the glass where you want it cut. You could even colour the entire glass if it's a small piece. Doing that makes it visible in the water. To remove the colouring, when the cut piece of glass is dry, use a clean rag and IPA. Some ink markers can't be removed in that way with IPA - so use acetone.

Al.
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