Test Equipment Anonymous (TEA) group therapy thread

[Cerebus]

Just what exactly are the properties of BeO that make it suitable for this application?

Very high thermal conductivity with low electrical conductivity.

Beryllia     209-330 W m^-1 K^-1
Diamond        1000
Copper            401
Aluminium       237
Alumina            30

Resistivity of berylia is 10¹² - 10¹⁵ ohm m.

[Andrew_Debbie]

Just what exactly are the properties of BeO that make it suitable for this application?

It very high thermal conductivity for an  insulator.   

I'm not sure if a modern less carcinogenic solution would be good enough here.      Hard to know if a someone simply picked the best thermal conductor without looking at options. 

I honestly don't see why it was used here.   The input bias is fairly stable inside the meter's specified operating range even with an air gap. 

-- It  only started to drift when the meter got cold.    - Even then it eventually warmed up and was stable. 


Of course in 1978 there were not as many options.    Could be a case of  an over specified design staying in because it was too expensive to change or simply because the person who made the choice was no longer on the team.



In 1978,  making a change meant redrawing the schematics and PCB layout by hand.   Expensive and time consuming.    There are some questionable  choices but I can see why it wasn't changed.

[med6753]

 I dunno... I have some of their epoxy and it does sortof smell like some jungle animal... 

mnem
takes forever to set, tho; so I rarely use it.

Gorilla CA glue sucks, big time. Never tried the epoxy but if it smells like ass as you state then it probably has the adhesive properties of a damp, sweaty, sticky ass. 

[mnementh]

What is your opinion aboot the change in mass of the junction? It seems to me the BeO disc was chosen for both thermal conductivity and electrical insulation properties...

The whole point of the assemblage is to keep the two transistors as near the same temperature as possible to keep input offset voltage from the temperature sensitivity of V_BE as close to fixed as possible. Any changes here are going to affect offset voltage and offset voltage drift with temperature. The offset voltage can be trimmed with the front panel offset pot, drift is minimised by maximising the thermal coupling of the two transistors. That this comes with a front panel offset adjustment suggests that the whole thing was not Mr. Stable in the first place so there's clearly no long term 'baked in' stability to worry about. With that in mind, going to the expense and trouble of a BeO washer attached to the tops of the cans in hoping to replicate a monolithic matched pair (that's how it's drawn so we must presume that at some point in its production history there really was a monolithic matched pair there) with just a matched pair smacks of magical thinking.

I found myself wondering aboot this myself... we were taught that this package needs wraparound heat sinks, and specifically to avoid the convenient options that clip on the top. I would expect similar from this application... but that would require something like a BeO sleeve around both parts... which would invite mechanical damage and exposure to BeO dust and... 

Yeah, okay. So it was a half-assed (okay, maybe 3/4-assed...?) attempt to solve 2 engineering problems and be economical to produce. I guess we should be glad it works as well as it does. 

mnem

[Cerebus]

Well, we don't know where the die attach actually happens in those cans but I'd be really rather surprised if I were to learn that it was to the top of the can - it's not impossible, but it's wildly unlikely. I suspect that the die is on a lead frame and is just floating inside the can in a glob of epoxy or, at the extreme, glass. The lead frame might touch the case. The problem with all the non-hermetic TO-x cases is that the internal construction is usually a mystery. If they've got a metal base then you can be pretty sure that is where the die is attached.

[AVGresponding]

*per earlier discussion  -  I'm an American expat in the UK.  My computer is set to UK English and I use an ISO-DE keyboard.   I ignore the red underlines and despise autocorrect.    Catalog Katalog catalogue.

Fuck autocorrect. I take ownership of my typos, and sometimes they make more sense than what I was intending to say anyway.

[factory]

The hp handheld 2000 count multimeter went a bit silly, way more than I was prepared to pay considering the crap pictures & high potential for a pile of battery corrosion inside. 
https://www.ebay.co.uk/itm/144244364494


David

[Robert763]

It's my understanding that Gorrila Glue (the classic one) is a gap filler that foams as it sets. Foam is the last thing I'd use for a themal connection.....
Super glue or epoxy woud be my choice.

[Andrew_Debbie]

Well, we don't know where the die attach actually happens in those cans but I'd be really rather surprised if I were to learn that it was to the top of the can - it's not impossible, but it's wildly unlikely. I suspect that the die is on a lead frame and is just floating inside the can in a glob of epoxy or, at the extreme, glass. The lead frame might touch the case. The problem with all the non-hermetic TO-x cases is that the internal construction is usually a mystery. If they've got a metal base then you can be pretty sure that is where the die is attached.

Q3,  has a brown epoxy? base.   Q5 is a mystery.     Removing it to have a look is not an option.

I don't think any of the leads on Q3 are directly tied to the case.  I did a check and the resistances were far too high.      I didn't do a diode check though  doh!

[factory]

Almost forgot to post this here....


David

[Martin.M]

The hp handheld 2000 count multimeter went a bit silly, way more than I was prepared to pay considering the crap pictures & high potential for a pile of battery corrosion inside. 
https://www.ebay.co.uk/itm/144244364494


David

the 2000 counts mean you are counting at minimum 2000 Webshops to get the batteries for your 427.
So, if they are fresh inside, the 100+ pounds may be allready 

[Robert763]

The OKi / METCAL PS800 that Mnem forced me to buy arrived today.
Fast delivery, very well packed, All complete including barely used tip and tip removal pad. Bonus items were a brass "scrubber tip cleaner and a anti-static curly cord 
It all works. Even more importantly the coil is the latest PS-CA3. Theis is the same as i used on the current PS-900 so the current SFV series tips fit.  The handle and coil alone cost twice what I paid.

[factory]

The hp handheld 2000 count multimeter went a bit silly, way more than I was prepared to pay considering the crap pictures & high potential for a pile of battery corrosion inside. 
https://www.ebay.co.uk/itm/144244364494


David

the 2000 counts mean you are counting at minimum 2000 Webshops to get the batteries for your 427.
So, if they are fresh inside, the 100+ pounds may be allready 

No, it was part of the listing. 


I think a DIY battery would have been the best option, but I didn't win it.

David

[mnementh]

The OKi / METCAL PS800 that Mnem forced me to buy arrived today.
Fast delivery, very well packed, All complete including barely used tip and tip removal pad. Bonus items were a brass "scrubber tip cleaner and a anti-static curly cord 
It all works. Even more importantly the coil is the latest PS-CA3. Theis is the same as i used on the current PS-900 so the current SFV series tips fit.  The handle and coil alone cost twice what I paid.

Suh-weet! Glad I twisted yer arm, then.



mnem
 

[Martin.M]

HP427A

open the empty battery ( Eveready 763 Type, = 22,5V ) ,
remove all what is inside, but the cover with the connection knobs is to re-use.
Insert 2 pcs. of Lithium 9V Blocks made for smoke detectors, they provide 10,4V each, in Series this works best.
Close the batterycase and put it back in the 427A.

The original Battery will suck 50$ from your bag + postage ..

[mnementh]

*per earlier discussion  -  I'm an American expat in the UK.  My computer is set to UK English and I use an ISO-DE keyboard.   I ignore the red underlines and despise autocorrect.    Catalog Katalog catalogue.

Fuck autodefect. I take ownership of my typos, and sometimes they make more sense than what I was intending to say anyway.

There... FTFY. 

mnem
*kicks Google Keyboard in the 'nads, just on GP*

[mnementh]

HP427A

open the empty battery ( Eveready 763 Type, = 22,5V ) ,
remove all what is inside, but the cover with the connection knobs is to re-use.
Insert 2 pcs. of Lithium 9V Blocks made for smoke detectors, they provide 10,4V each, in Series this works best.
Close the batterycase and put it back in the 427A.

The original Battery will suck 50$ from your bag + postage ..

Sounds like a job for 3DP.

mnem
*drops back and punts*

[mnementh]

Looking at that listing for the 427A, this came up at the bottom of my screen: https://www.ebay.co.uk/itm/403226626870

Still a hour to go, tho...

This too: https://www.ebay.co.uk/itm/334181815293

And that one's grandpa: https://www.ebay.co.uk/itm/313709878481

And a Keithley in the US with recent Cal: https://www.ebay.com/itm/255173111195

mnem
             
*nibbling on a pig chip*

[mansaxel]

 I dunno... I have some of their epoxy and it does sortof smell like some jungle animal... 

mnem
takes forever to set, tho; so I rarely use it.

Gorilla CA glue sucks, big time. Never tried the epoxy but if it smells like ass as you state then it probably has the adhesive properties of a damp, sweaty, sticky ass. 

I've had my face glued together using medical CA. It smells the same as the Loctite gel CA that's most prevalent here. It is a madeleine cookie back to an ER in Carcassonne, where I was driven by les sapeurs-pompeurs after trying to knock down a footbridge with my forehead. (The bridge won). They used the gloo for the smaller cuts after spending 27 stitches on the big hole.

[mansaxel]

The hp handheld 2000 count multimeter went a bit silly, way more than I was prepared to pay considering the crap pictures & high potential for a pile of battery corrosion inside. 
https://www.ebay.co.uk/itm/144244364494


David

the 2000 counts mean you are counting at minimum 2000 Webshops to get the batteries for your 427.
So, if they are fresh inside, the 100+ pounds may be allready 

The meter has Option 01, mains power. Mine too, even so modern it has a C14 inlet. I removed the completely dead battery, and am running it from mains ever since. It's a desktop meter, it can be mains powered! If one insists, I believe threetwo 6F22 in series would be a sensible bodge, IIRC.

[mnementh]

 I dunno... I have some of their epoxy and it does sortof smell like some jungle animal... 

mnem
takes forever to set, tho; so I rarely use it.

Gorilla CA glue sucks, big time. Never tried the epoxy but if it smells like ass as you state then it probably has the adhesive properties of a damp, sweaty, sticky ass. 

I've had my face glued together using medical CA. It smells the same as the Loctite gel CA that's most prevalent here. It is a madeleine cookie back to an ER in Carcassonne, where I was driven by les sapeurs-pompeurs after trying to knock down a footbridge with my forehead. (The bridge won). They used the gloo for the smaller cuts after spending 27 stitches on the big hole.

Yes, I expect the only difference between that and the Dollarama CA is it has a verifiable sterile production COC. Functionally... CA is itself a pretty effective antibiotic... most biots encapsulated in CA don't remain active for long. 

mnem
*toddles off to do something constructive*

[Martin.M]

a Question about 427A:

The banana jacks don`t fit standard banana plugs perfekt,
seems to be larger holes there, not exactly 4mm.
Is the a special set of wires for the 427A?

[Cerebus]

It's my understanding that Gorrila Glue (the classic one) is a gap filler that foams as it sets. Foam is the last thing I'd use for a themal connection.....
Super glue or epoxy woud be my choice.

Yes, it's an addition cure polyurethane. It cures as it absorbs atmospheric moisture and produces CO₂ as a waste product. It's basically the same formulation as the gap filling polyurethane foams beloved of bodging builders the world over (including myself, the gaps between my living room window frames, the wall next to them and the drylining in front of them are full of the stuff).

[Vince]

[...] in Carcassonne, where I was driven by les sapeurs-pompeurs

Oh my.... 

[factory]

a Question about 427A:

The banana jacks don`t fit standard banana plugs perfekt,
seems to be larger holes there, not exactly 4mm.
Is the a special set of wires for the 427A?

4mm banana leads from Pomona should fit fine, I believe ITT/Pomona were the OEM hp used for some banana test leads & adaptors.
https://uk.farnell.com/pomona/b-36-02/stack-up-banana-plug-plug-15a/dp/2917800?ost=2917800
https://www.farnell.com/datasheets/2645545.pdf


David