Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
Robert763:
--- Quote from: Roehrenonkel on January 13, 2025, 03:27:54 pm ---Hi Vince,
--- Quote from: Vince on January 12, 2025, 05:33:47 pm ---Do old beards here remember such things ??
--- End quote ---
Yeah, sure, i still have a dozen or so left. :-)
Ciao4now
--- End quote ---
Those are anodised aluminium alloy. Quite different to what Vince has pictured. The little tag is where they connected and hung them for the anodising.
Doh read to end of thread before posting.... :palm:
Vince's does look like a bare metal. Tin would be my next guess. Soft, density about right and better conductivity than lead.
IF you find it try touching with a soldering iron..
Robert763:
The parts That I thought I needed to repair the THS720 input fault arrived today. Three surface mount relays. The exact parts are hard to come by. They are a small signal latching type with two 4.5V coils. Part number is EB2-4.5TNU. An odd voltage given that the drive circuit is 5V via a PNP transistor. If I recall correctly the old IBM Token Ring network hubs used 4.5V latching relays. Maybe these are a throw-back to them.
Anyway after looking at the relay specifications and 720A circuits I decided that the standard 5V version EB2-5TNU relay should be OK so that is what I ordered.
Took the 720 apart. Just 4 screws and then everything is either held by friction with foam pads or plastic clips. The hybrid is under a tinplate screen. This was clipped in before it was soldered making removal a bit tricky. There is very little space between the relays to de-solder or solder them. Decause of this and assuming they all had similar amounts of use I'd already decided to change all 3. Even then had to make up a special soldering iron bit extension to solder the new ones in.
It's a bit of a PITA but it's all working now and I have a THS720P for under £250 8)
AVGresponding:
--- Quote from: Robert763 on January 15, 2025, 05:42:18 pm ---The parts That I thought I needed to repair the THS720 input fault arrived today. Three surface mount relays. The exact parts are hard to come by. They are a small signal latching type with two 4.5V coils. Part number is EB2-4.5TNU. An odd voltage given that the drive circuit is 5V via a PNP transistor. If I recall correctly the old IBM Token Ring network hubs used 4.5V latching relays. Maybe these are a throw-back to them.
Anyway after looking at the relay specifications and 720A circuits I decided that the standard 5V version EB2-5TNU relay should be OK so that is what I ordered.
Took the 720 apart. Just 4 screws and then everything is either held by friction with foam pads or plastic clips. The hybrid is under a tinplate screen. This was clipped in before it was soldered making removal a bit tricky. There is very little space between the relays to de-solder or solder them. Decause of this and assuming they all had similar amounts of use I'd already decided to change all 3. Even then had to make up a special soldering iron bit extension to solder the new ones in.
It's a bit of a PITA but it's all working now and I have a THS720P for under £250 8)
--- End quote ---
Given I have effective unlimited access to old fire alarm equipment, it's a shame that the working voltage in such systems is 24V (nominally, usually; there are 12V systems but they are uncommon). It makes the high quality parts inside (such as this exact relay type) mostly unusable in home projects/repairs.
bsdphk:
--- Quote from: Vince on January 13, 2025, 06:29:20 pm ---My stuff is lead by any way you look at it. Density alone though crudely measured, can't be aluminium nor iron.
--- End quote ---
Apart from being banned for toxicity these days, lead is not a bad choice for the job.
Lead is a quite decent thermal conductor, 30-35 W/mK, depending on alloys, it is ductile, stable, and not too dangerous (ses also: Beryllium).
For comparison mica comes in at .43 W/mK so it has to be 70 times thinner than lead for same thermal performance, but it is hard and brittle, so you also need thermal compund etc.
Of course mica is an excellent insulator, lead is anything but, but in most typical applications, oxidizing the surface will probably be sufficient, and the black-ish color on your picture may be just that, so dont clean them too much ?
In theory one can bolt a semiconductor directly to a properly anodized alu heat-sink, but it takes insane care and cleaning to avoid particles or surface imperfections from breaching the insulating oxide layer, both during initial assembly and subsequent mechanical shocks.
Robert763:
--- Quote from: AVGresponding on January 16, 2025, 06:07:38 am ---
--- Quote from: Robert763 on January 15, 2025, 05:42:18 pm ---The parts That I thought I needed to repair the THS720 input fault arrived today. <SNIP>
--- End quote ---
Given I have effective unlimited access to old fire alarm equipment, it's a shame that the working voltage in such systems is 24V (nominally, usually; there are 12V systems but they are uncommon). It makes the high quality parts inside (such as this exact relay type) mostly unusable in home projects/repairs.
--- End quote ---
I have lots of 28V (yes 28) and 115V 400Hz components. They are pretty useless outside aviation. I have used the relays in applications where I can decide the control voltage.
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