Electronics > Metrology

General Radio 1403A 1000pf capacitor adjustment

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Labrat101:
Invar is magnetic check with a small magnet

Labrat101:

--- Quote from: Henrik_V on June 15, 2021, 03:43:28 pm ---
--- Quote from: Conrad Hoffman on June 15, 2021, 01:50:55 pm ---I thought the 1404 plates were invar, but not the 1403. Have to check that.

--- End quote ---
Don't know for the 1403, but the 1404 and 1406 are invar.


I don't think there is any aluminium in the 1404 ... haven't found some :)

Our plan is to polish the invar plates and maybe have them (and the bolds,spacers...) gold plated  ;D 8)  , more important is the removal of the tin/solder plating of the brass(?) housing parts to prevent whisker.  Maybe will be tricky for/around the throug-hole plating ...  But a very good workshop and galvanic is inhouse :)   also vacuum/ Nx refill / clean room/ temper  all there... but time and motivation ....since we have nice&stable working 1404 .

I attached a picture of one of those and marked a wisker... probably posted before ..

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Interesting idea about Gold plating . I would check that this is feesable as in the use of 2 Dissimilar Metals
 I think that the extra cost of gold plating during manufacture would not increase the cost of these units very much
 I guess that this process is not good when it comes to high tolerance caps . I would check on what the overall effects are.
 I have never seen gold used in this way .. except in Aerospace and that's for a different reasons.

 

Henrik_V:

--- Quote from: Labrat101 on June 15, 2021, 04:49:14 pm ---Interesting idea about Gold plating . I would check that this is feesable as in the use of 2 Dissimilar Metals

--- End quote ---
I expect that one or more additional layers of some other elements will be needed, but that up to our galvanic experts :)

Conrad Hoffman:
I used to work for a place that made optical equipment out of invar and had the parts plated. Only plating shops that really know what they're doing are successful and I still don't trust the stuff. Even with a good flash of copper or whatever else they use, adhesion over time can be tricky. I've seen a lot of lifted and peeling plating. Invar has so much nickel that it should be pretty good if the environment is good. Even lying around in the uncontrolled shop, the stuff would slowly develop a haze, but not really corrode. I suspect a polished surface, something we never did, would be resistant to oxidation.

Labrat101:

--- Quote from: Conrad Hoffman on June 16, 2021, 08:09:08 pm ---I used to work for a place that made optical equipment out of invar and had the parts plated. Only plating shops that really know what they're doing are successful and I still don't trust the stuff. Even with a good flash of copper or whatever else they use, adhesion over time can be tricky. I've seen a lot of lifted and peeling plating. Invar has so much nickel that it should be pretty good if the environment is good. Even lying around in the uncontrolled shop, the stuff would slowly develop a haze, but not really corrode. I suspect a polished surface, something we never did, would be resistant to oxidation.

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You right what you say also Invar & Gold is in the wrong place on the periodic table
which is why  copper or any plating will peal as the dielectrics of Invar has a very good temperature stability and copper or silver are the opposite and will peal off.
separate due to the chrome content .
Invar as you said has a very resilient surface and pure chrome is almost as tough as titanium .
 

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