Removing Meter Face-Plates - UK Vintage Radio Repair and Restoration Discussion Forum

Bazz4CQJ · 25th Sep 2022, 9:34 pm

Something like 50 years ago, the Edwards Company was the leading supplier of all things to do with vacuum equipment. One of their products was a Pirani gauge, which measured vacuum, and displayed its reading on a standard moving coil meter with a log scale in calibrated in Torr: not too much use for radio work.

The FSD of the meters was 1mA and I think they were made by Sangamo Weston. I have a couple of these meters from old discarded gauges. Attempting to take off the front cover to paste on a 0-1 scale, I found it impossible to get the cover off and ended up breaking the brittle plastic. I could not see any screws, fixings or adhesives that needed dealing with. The outcome was pretty poor, needed sticky taping and it is now at the bottom of the junk box (see attached).

Has anyone any experience with working with Sangamo meters?

Thanks

B

Tractionist · 25th Sep 2022, 10:52 pm

I have no experience in this particular area/endeavour .... but - have you tried a little judicious heat?

vidjoman · 26th Sep 2022, 8:44 am

Most plastic fronts that I've encountered just clip on around the edge. Look from the back and see if you can see the join.

Kentode · 26th Sep 2022, 12:40 pm

They may be welded by ultrasonics. In my thirties l worked in a factory that used this process to prevent tampering.

When l first started lt was painful to walk past the machine when it was operating, but when I left nine years later l couldn't hear it at all!

Bazz4CQJ · 26th Sep 2022, 1:01 pm

Thanks for the suggestions. Over the years, I've successfully removed the front covers off quite a lot of meters; as often as not you can see 2 or more little mouldings which just need gracefully sliding over the edge of the main body.

But this was distinctly different; I could not see any feature which retains the cover and which would be a starting point. Even with warming, the plastic seems to "super brittle" (perhaps not surprising given the age). With the first one, I effectively wrecked the cover getting it off and the annoying thing is that no matter how hard I look at what's left, I don't understand what held what, and learned nothing in process.

Ultrasonic welding is a possibility. All I can conclude at this stage is that Sangamo did not want intruders to get inside their meters, and putting a new scale on them seems to be impossible?

B

25th Sep 2022, 9:34 pm	#1
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,934	Removing Meter Face-Plates Something like 50 years ago, the Edwards Company was the leading supplier of all things to do with vacuum equipment. One of their products was a Pirani gauge, which measured vacuum, and displayed its reading on a standard moving coil meter with a log scale in calibrated in Torr: not too much use for radio work. The FSD of the meters was 1mA and I think they were made by Sangamo Weston. I have a couple of these meters from old discarded gauges. Attempting to take off the front cover to paste on a 0-1 scale, I found it impossible to get the cover off and ended up breaking the brittle plastic. I could not see any screws, fixings or adhesives that needed dealing with. The outcome was pretty poor, needed sticky taping and it is now at the bottom of the junk box (see attached). Has anyone any experience with working with Sangamo meters? Thanks B Attached Thumbnails __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

25th Sep 2022, 10:52 pm	#2
Tractionist Heptode Join Date: Apr 2016 Location: Cheltenham, Gloucestershire, UK. Posts: 875	Re: Removing Meter Face-Plates I have no experience in this particular area/endeavour .... but - have you tried a little judicious heat? __________________ Red to red, black to black. Throw the switch and stand well back!

26th Sep 2022, 8:44 am	#3
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Removing Meter Face-Plates Most plastic fronts that I've encountered just clip on around the edge. Look from the back and see if you can see the join.

26th Sep 2022, 12:40 pm	#4
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,301	Re: Removing Meter Face-Plates They may be welded by ultrasonics. In my thirties l worked in a factory that used this process to prevent tampering. When l first started lt was painful to walk past the machine when it was operating, but when I left nine years later l couldn't hear it at all! __________________ Regards, Ken. BVWS member

26th Sep 2022, 1:01 pm	#5
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,934	Re: Removing Meter Face-Plates Thanks for the suggestions. Over the years, I've successfully removed the front covers off quite a lot of meters; as often as not you can see 2 or more little mouldings which just need gracefully sliding over the edge of the main body. But this was distinctly different; I could not see any feature which retains the cover and which would be a starting point. Even with warming, the plastic seems to "super brittle" (perhaps not surprising given the age). With the first one, I effectively wrecked the cover getting it off and the annoying thing is that no matter how hard I look at what's left, I don't understand what held what, and learned nothing in process. Ultrasonic welding is a possibility. All I can conclude at this stage is that Sangamo did not want intruders to get inside their meters, and putting a new scale on them seems to be impossible? B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.