Electronics > Metrology

General Radio 1403A 1000pf capacitor adjustment

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Labrat101:
Hi I would not try opening the nuts they are torque set .
If its that far out I would wash it very care fully in IPA . even better an ultrasonic bath .
If dirt dust has got between the plate it will have become static charged to the surfaces .
 so while cleaning it make sure the out terminals are shorted .
If you have loosened any of the clamping nuts . Find one that you have not opened and with a
stainless steel torque key measure the release pressure and the reset all the lock nuts to the same.
when these are assembled they put shims between the plates so they are all parallel to each.
That Last picture looks like it has been knocked and bent .
I would get hold of some Plastic feeler gauges and measure the good plate distances.
 These unit are also dependent on air . so altitude is also part of the calibration & temp.

Henrik_V:
The one pictured is one of a batch made by Quadtech and cans only, most of them failed due to wisker and in some you hear something is jingling inside while shaking. I harvested them out of the dumpster.
We opened some cans (the 1404 cans are sealed and filled with nitrogene to avoid the influence of humidity) hot air didin't do the job, we used a torch  ;D
(and vented the cans first  >:D)
... the one showed dropped  on the floor :-//  some of the plates are bended. However still enough parts for CDs cap.

Maybe one day we rebuild some without solder plating in the housing and polish the plates (the genuine GR ones definitly look better than the successors)
 

Conrad Hoffman:
I thought the 1404 plates were invar, but not the 1403. Have to check that.

Labrat101:
I am glade you rescued them from near death . ..
 There are a few rules when working with this type of aluminium . Most people don't realises that
aluminium oxidizes in air .Oxygen  just scratching aluminium under a high power microscope the
surface of the scratch looks like its alive and the oxidisation starts happening in a few seconds.
aluminium oxide is not a true insulator more like a semi conductor and the particles are very small and
are always particle charged . Under clean room involvement they can cause a lot of problems in the hyper
filter as the static charge created by the dust can under certain frequencies produce 10kv plus.
so the the plates should only be handled with cotton gloves as not to add oils or other contaminates to
the anodized surface . aluminium is the metal form of Ruby and we all know when ruby is excited we get
light Lazar .
So polishing the plates will cause more harm . clean them with ultra pure DI water . Or IPA .
 And when reassembling at home I use to do it inside a large plastic bag  which helps to keep dust and
moisture limited . (heavy breathing & coffee )
One of those units looked very nice probably the one that was nitrogen filled The pressure is normally
1 bar (14.7 psi) which will give the calibration @ Sea level and wont be influenced by outside pressure
changes .
I'm sure you will get these back within spec with a Lot of Love & tender Care .
 

Henrik_V:

--- 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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