Hewlett Packard 4440B Decade Capacitor.

[beanflying]

A fairly old and rare beast arrived in today's mail from Brisbane via Evilbay. The Photos on the add looked fairly grubby and knocked around but I thought it was worth a look for not many $$.

Quick check on my 'best' Capacitance meter showed all ranges working very well. The Box is Rated at 0.25% makes my hunk of junk $7 special look not bad.

In person it has certainly been well used but the outside was better than I thought. Rubber Feet have perished and the corners of the plastic bit of the case need a bit of love. Some cleaning of the metalwork and outside will come up nicely.

The Body of the unit is bonded to the Earth terminal on the front of the case but isolated from the Inner Aluminium box by the Plastic side frames it is fixed too to provide more safety at higher voltages. Undo a few screws and ....... 

Link to Manual http://exodus.poly.edu/~kurt/manuals/manuals/HP%20Agilent/HP%204440B%20Ops%20and%20Service.pdf

[beanflying]

Inside it consists of 3 main decades driven from some interesting Cam drive stitches in a binary layout meaning only 4 Caps are needed per decade. All caps as per the manual are Silvered Mica which should make them stable for a long time yet.

The lower decades are different in construction with trimmers and the final stage is a Capacitor Gang with a series of tuning gangs to tweak it throughout it's range.

[beanflying]

Not sure how the higher decades are constructed internally as they are fully sealed. I will try and get some better shots of the lower decades but looks like desoldering would be needed at this stage so unlikely to happen.

Cleaning the switches will present a similar problem with access. Proper read of the manual is in order which does include full calibration methods for the lower decades.

Cleaning time.......

[beanflying]

This is as far as the teardown goes. Any further involves Jesus clips, springs and most likely several hours of 

The switch contacts are all over the shop from 1-3mOhms to over 10 ohms  Time to break out my fathers relay tweaking tools and some long cleaning sticks.

Apart from the interesting decision to use threaded knobs on parallel shafts  nothing much else of interest apart from the phenolic shaft on the lower gang.

[beanflying]

Switches cleaned and tweaked all contacts under 3mOhm and most 1-2mOhm. Broke out the Big Kev Goo Remover for the stickers followed by some IPA so it smells less citrus like on the outside.

Tested all ranges on my Classy $7 meter and see what it got  Not sure I need a 'proper' LCR meter at present.....

Ready for the next few decades of it's life.

[kj7e]

In the late 80's when I was about 10, I was first getting started in Ham Radio and electronics.  All I could afford at that time was 1950's and 60's used gear from swap meets.  I had a room filled with old HP gear, 524D Frequency counter (later a 5245L), 608D Generator, 410B VTVM, 200CD oscillator, 175A scope, 3440 digital voltmeter and so on...  Love the 1960's HP gear, they don't make things like they used to.  No shortcuts, everything was built to last.