added the lower arms to the loop

I had a little shop time this afternoon and put the lower arms on the loop.

As I push the center up the tips swing down and in. the lower arms swing up and the small section between the arm tips fold down over the lower arm tips.

My string slipped and gave a little slack. When it is secure it will fold into a nice little package. I left the lower arms longer while adjusting them. I will trim them and the the dowel before I put the wire on. I should have the wire Friday.

note: the lower arms are attached with small hinges.

A little more about the center joint.

I didn't get much shop time today. 
I did determine the next step on the build and decided it was a go so ordered some wire. Where I left off yesterday.

I used a scrap of popular I had cut 1/4" thick to make the plates at the center. You can see in the picture it warbled a little as I closed the loop. I added a couple more dowels close to the center pole at the top of the squares. This hold the squares in line, preventing the warble. Let's take a closer look at the center beam and beam ends.

You can see as I pushed the center up the tips folded down. The horizontal was at the point I drew the red line. The red to green is the amount of overlap I would expect if the bottom beam was the same length. The wires will have to fold back on themselves. The distance of the fold back is represented by the blue box. This is why the bottom beams are shorter than the cross beam.

The wire I ordered is a flat ribbon like lamp cord. It is four conductor 22 gauge. I made the plastic tubing long enough to put 2 wraps on either side of the beam. This would give 16 turns. When I tie the ends together it will give five taps. The taps being at 0 Turn 4 Turns 8 Turns 12 Turns and 16 Turns.  

The one I'm using for a pattern has 6 terminals so I'm thinking 5 will be good. The bottom beams will be mounted with hinges and the wire ribbon will be attached to the plastic tubing. It could be laced or attached with Duco Cement, Yet to be determine.

Proof of concept of the loop mechanism

The mechanism seems to "lock" in the down position holding tension on the wires. It might be better explained that the cross bars weight is pulling down on the wires and holding them in place.Take a look at the loop again.

As you look at the loop think about an umbrella. You push the center up and the outer tips fold down. With the loop we have the added action of the lower arms folding in. So the tip folds down as the lower arms fold in and we end up with the tips holding the lower arms in against the vertical pole. That's a lot of pivoting. It calls for four pivot points, two in the center of the vertical pole and two at the bottom.
I had a little shop time this afternoon and this is how it went.

This cherry board was left over from a cabinet build and it looked like what I needed. I set the saw to make squares from the board.

One board made five squares. I ran them through the planer to smooth saw marks and make them all the same size.

I need something to support the wires. This sink supply looks like what the doctor ordered.

I cut the sink supply in 3" pieces. and am ready to start the construction. Two 20" pieces are overlapping the center piece 4". I drilled a 3/8" hole at the end of the center piece and inserted a piece of the plastic tubing in it. Clamping the three pieces together before drilling the holes to tie them together insures the holes line up. I drilled 1/4" holes and put a piece of 1/4" dowel in it. Using wooden nails seems a good idea because I was cautioned not to put magnetic material in the loop. The shoulders created by the side pieces support the cross bar.

I used 2 16" pieces for the cross piece. Putting a piece of plastic on the end to make a place for the wire. I cut the end of the cross piece at a 45 degree with the cut starting at the center. turning the cut down allows the cross piece to "butt" the vertical pole when in the position shown. When you push it up the missing corner allows it to pivot.

I used 2 pieces of flat board to tie the center joint. Just 1 pin on either side of center allows the joint to pivot.

I tied a string on the post to see how it functions. You can see I pinned the vertical together with long pins. They need trimming after the glue cures.

 Back to the beginning. The cross bar holds tension on the upper wires and the lower bars hold tension on the lower wires. Pushing the center up umbrella style allows the cross bar tips to lower. which give slack to the lower wires and allowing the lower bars to fold in making a nice compact storage unit.
Maybe tomorrow I can put the lower section together.
looking good so far.

Loop building data

Antique loop advertisement

A builder making reproduction

Some design data

The above data can be used to determine size and shape for the antique loop. I think I will build this one.

It doesn't appear to be to difficult a project.
Just as a matter of interest the one above was auctioned for $750. (If my memory is correct.)
Hopefully tomorrow will have some shop time and the project will begin.

K2539 Amp rebuild

This is my new go to amp. ( I may remove the first stage.) It is almost to high gain. The one I made last night was great BUT I added a switch and rearranged the circuit in the build I did tonight.

 The lower one was a 1-1/2 volt Germanium transistor version of the hearing aid amp. The smaller board on top is the 9 volt JFET version. It worked so well I decided to do another and add a switch and battery tie points. To test it I connected 2 DVM's set on the 200 mv range and a signal generator. I have the ear buds plugged in so the reading are loaded values.

 Let's see .03mv = 30 uv input and 11 mv out, very good.

 The amp was to sensitive. It would hum when i put my hand close to the input. I placed a 1nfd cap and 510 Ohm resistor across the input. This helped bypass noise to ground. The readings were all taken with the input bypassed.

The next step will be to place an attenuator on the input and a demodulator to feed it. I thinking Gilbert Cell.
I'm still considering removing the first stage. I clipped a diode with a antenna across the second stage input and hear my local station. It may need the first stage for weak signal reception????? Time will tell.

Poor man's double sided circuit build of a 3 JFET amp.

The ground plane is very important and a good practice is to use a double sided board. Making one foil +Vcc and the other -Vcc. So what do you do if you have no double sided circuit board? Order some from a supply house or maybe just what you have available and make your own.

This old rough cut 2 X 4 is what I was looking for. It was used to chock some material shipped to a construction site. It would be land fill had it not found its way into my shed.

I chopped a short piece from the end of one to make it easy to handle. The sliced some thin pieces from it. I did not measure just something around 1/4".

I laid it on a magazine so I don't make a mess on my desk top.

I applied a coat of contact cement and get some aluminum foil for the laminate. What I'm using is not as thick as you might like but it was in the shop.

After the glue set for a couple of minutes I applied the foil.

I turned the page in the magazine to get a clean surface and laid the blocks facing up. Apply a coat of cement.

After a couple of minutes fold the foil over on the blocks and let it set a while so the glue can cure.

A sharp knife or razor blade can be used to cut the laminated blocks out.

 And we now have three double laminated bread boards. You could use flashing or a can just whatever is available. I like the coffee can bottoms. They are large enough and flat. Hair spray cans are good too.

As you can see it is a little ragged. You can sand or file the edge smooth but as long as it doesn't short out a little fuzz will not hurt.

This one is a little crinkled. You can use a putty knife or old playing card to work out the wrinkles I just was sloppy I guess? It will work wrinkles and all just not as pretty as it could be.

The large breadboard is poster board. It is the amp I posted 2 or 3 post ago. The little one is the double sided board version. I left the leads full length on the poster board version so i can reuse the components.

I used the copper foil glass workers use to solder stained glass with to make my solder points. I mounted all the transistors on little insulated islands and then added the grounded components. The +Vcc being on the bottom foil I just drilled holes sized to the wire and the used a 1/8" drill to drill through the foil on top. this allows the leads to pass through without shorting. The little amp is a good one. I would think you could use any JFET available to you. The biasing may vary a little but the worst case would call for adjusting the source resistor.

I used pasta maker manhatten pads to mount the transistors.
manhatten-pads-with-pasta-maker.html

If you don't have the board for the pads you can make them using copper foil or old tin can strips laminated to craft paper. Just use what's on hand and some imagination.

2SK2539 three stage AF amp

I built the circuit from 2 post earlier and it worked very well. I thought I would try it in JFET. This is what I came up with.