Homebrew Can Capacitors.

[Station X]

In the near future I hope to be restoring a New Zealand Wireless Set ZC1. Visual inspection showed that two of the three dual 10uF can capacitors had been replaced with components which looked nothing like the originals. The third cap had been broken away from its base. I tried to obtain three identical sized cans for restuffing, but this proved impossible. Another possibilty was to use Steradent tubes, which are the correct size, but crimping the base in would have presented problems. So I decided to make new cans from scratch.

The original caps were a bit like top hats, a bit like a very tall 2N3055 cans. These were fitted from under the chassis which made removal very difficult. For that reason I decided to use conventional mounting brackets fitting the holes in the chassis and I made those too.

The pictures should be fairly self explanatory. I'm a tight fisted radio amateur, so most of the parts came from the proverbial scrap box. The 1" diameter alloy tubing is from an old TV aerial pole, the top caps were machined from old heat sinks and the base insulator is made from copper clad board with the copper etched off. The only parts bought in were the capacitors which are 450V DC 10uF 105 deg C types with a 140mA ripple rating.

The top caps are held in with araldite. To hold the base insulator in place a shallow recess was turned in the end of the tubing to be a close fit on the base. The edges were then gently peened over with a small hammer. I made the cans slightly longer than necessary, so that if restuffing is needed in future the tube can be cut through just above the base and a new recess cut in the can.

The solder tags are held to the base with screws nuts and washers. The capacitor leads pass through small holes adjacent to the tags and are soldered to the tags OUTSIDE the can. This means that loose nuts can't lead to high resistance connections. The positive leads are sleeved, which together with a cylinder of cardboard inserted into the can, prevents them shorting to the metal. I had intended that the negative connections should be made to the can. I have often soldered aluminium in the past by cleaning and soldering it through a film of oil, but it just didn't work with this particular alloy. Thus a third tag was added and placed close to the can. In theory this could be bent back and trapped under the mounting brackets, but I think wiring it across to a tag held by the mounting screws will be better.

Before final assembly the capacitors were tested for capacitance and leakage at the full working voltage.

I have yet to label the cans, but will probably make labels using a labelling machine with silver label tape.

Off the shelf mounting brackets were no good as they wouldn't fit the holes in the chassis, so I made those too. This took longer than making the cans. No amount of calculation or making cardboard templates resulted in the lugs being in the right place. Finally I made them far too large, rolled up the bracket and filed them to the correct size and position.

If I make any more of these capacitors I will position the negative tags further from the cans and devise an arrangement for spinning the bottom crimp rather than peening it. That should make for a neater job.

The next thing I have to do is make a solid state vibrator for the same rig. Watch this space.

[Robert Darwent]

Those caps look very authentic, great work Graham! Well worth the effort IMHO to retain the original look of the chassis.

Regards

[HamishBoxer]

Excellent!
David
also bvws and rsgb member

[MichaelR]

Graham,

I am not one for going to the trouble of restuffing failed electrolytics and I will not take that any further however I must congratulate you on your making new cans and excellent finished product.

I do agree the NZ set deserves it. Some sets I must admit need to have the original cans on the chassis , the R1155 is a case in point , just does not look right without them.

Well done

Mike

[Mike Phelan]

Nice work, Graham, and the sort of thing I like to do!

[Aerodyne]

The pleasure of a job well done is profound (I'm thinking of entering for one of the poetry competitions... not really...-))
Very neat work, Graham, and a clever use of scrap materials too.
Very impressive.
-Tony

[Station X]

They have labels now. I used a labelling machine loaded with black lettering on clear tape. This lets the aluminium show through. I resisted the temptation to add a makers name such as "Shunts"

[Radio_Dave]

Very impressive, well done Graham

Regards
David