The start of the build of a replica Paraset

NOTE on cad files

Our laser cutting files do not have every hole included deliberately, when compared to other cutting patterns on the web. If we put every original hole in you might get stuck for a part that has to have those hole centres.....since we leave some holes out as you can soon drill them if needed.

Do you need a flat pack or folded pack of the metal work?

If you have no access to a laser cutter and would like a flat pack, or a folded pack then please email directly at:-

gw.woo@btinternet.com

and he will reply as to the possibility of supplying such a pack to you.

If you would like to have the chance of replica knobs for you Paraset click here

If you have not read the "How our Paraset works" section then please have a look there as many of your questions will be answered !!

Explanation for C2 is here

Explanation for C7 is here

Explanation for C9 and 9a is here

Here is a picture of some of the metal work as received from the laser cutters and also a chassis that has been folded. The laser should have marked out the folding lines for you, do not remove these when you sand the surfaces. If you look at the picture you can clearly see the folding line as etched by the laser on the bottom part which forms the box.

At this stage one needs to emery off all rough edges and all surfaces now whilst they are flat. Use emery cloth (or sanding paper if that's what you have) to remove all razor sharp corners...don't "round" them off, just remove the sharp corners so you cannot get cut by them when performing operations !

Use a file on all those edges to be soldered, as the laser cut edge will be "blued" slightly making it difficult to solder later.

I de-grease the parts using hot soapy water, you might like to use some sort of de-greaser. Leave the parts to dry. When dry you can proceed to the next stage which is folding the box, lid, chassis and lip.

16th July 2010

We like to think that our laser cutting files do produce a good box if folded with a little care. Don't rush.

You might like to read this before bending your box.

Here you can see the bending operations needed to fold the box, lid and chassis. Fold the box using two bits of angle iron in the vice and a block of wood (very hard wood...oak) and fold the ends into the sides...just. This will ensure an overlap making a good solder joint and the chassis will fit into the box nicely.

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6

7

A pleasing result we think. This leaves the lip to be bent and fitted and then cut to length but this is only done after the box and lid are built and soldered at the corners.

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Now drill out the corners with a small drill (the holes already exist having been cut by the laser) these holes being there to help bending operations. Drilling them out removes the blue surface allowing the solder to take.

Make sure each side fits correctly and stays in position then, If you can, pre heat the metalwork on the gas stove just a little and using a large soldering iron (60w or more) solder the corners.

Clean the strap of all blue edges and sand clean and degrease. Now bend the strap to fit tightly to the edge of the lid. I know it is too long.....you cut the excess off later.

Tack the lip using solder and check it fits halfway over the edge of the lid. Then pre heating just lightly if you can solder along the lip securing it to the lid. Solder a couple of inches at a time and squeeze the lip tightly to the lid using small pliers.

Trim off the excess and file the edges. Dress the edges of the box and lid using a file and then sand clean. Here is a picture of a finished box prior to sanding clean ready to fit a hinge and then paint. We hope you like it.

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Make your antenna and earth sockets and crystal sockets from some brass bolts. File the head down until it is flat...or if you have a lathe use this. Now grip the bolt in the vice and drill down it with ever increasing size drill until you get to 3mm. Yes sure, the first one you drill you will come out the side of the bolt! But you will get the skill required after a couple of attempts and drill the holes correctly. Of course if you have a lathe......use that.

Incidentally grip the bolts in the vice using a couple of nuts on the bolts, this way the thread is not damaged by the vice...or lathe chuck come to that!

In the photo you can see two such sockets, they are fitted with insulating washers and a small insulating sleeve (made from the outer of white co-ax cable) which prevents the bolt from shorting to the chassis. The finished ones look very close to the original type fitted except for the brass colour!

In the back ground you see some odd bolts lying around, I used 0 BA sized bolts. You will need four and don't forget you will need four nuts and four insulating washers and two solder tags to fit the bolts.

Rub down lettering.

With the preparation done for painting the front panel it was sprayed with normal crackle finish "Hammerite". After the paint has dried the lettering can begin.

We use rub down lettering on the Paraset front panel. As you can see in the picture this lettering can be purchased from "WHSmiths" or similar shop. It comes under a variety of names such as "Letteraset" or "Dry Transfer lettering" etc. There is a skill required to get this to look good when completed. Here are a few pointers....

1 If you have access to a pc, great, start a new word document and type in each word (capitals please!) and centre justify each word. Between each word type in the letter "I" twice. Once they are all typed in and the pc has centralized them you can now see at a glance where the exact centre of each word is. Now you know this you can place the lettering in the right place with respect to the controls.

3 If the letters are not in a straight line, not spaced correctly.....in short anything that makes the wording look wrong then it is wrong. Take it off, using sticky tape to attract the letters/word that is at fault and do it again. It will be no good if you leave it as your eye will always go to the faulty lettering.

4 Varnish over the lettering with satin or matt polyurethane varnish or similar. Don't touch the panel for a couple of days allowing the varnish to harden. To damage it now will really give you a headache to repair it.

To make a change from all that lettering which can be boring (!) I fitted the insulated dial pointer.

As you know the Paraset has a built in key...which some folk find hard to use and would like to use an external key.

I fit an insulated dial pointer ( which cannot be seen easily ) and connect this to the keying circuit.

Now I can use an external key by connecting it to this insulated pointer using croc clips the other side of the key going to the chassis. You like?

If this is for you make and fit it now. I use fibre washers to insulate the pointer from the chassis.

Have a good close look at the pictures.

Now the matt varnish has dried on the lettering some of the hardware can be added. You will notice this paraset has an additional variable capacitor fitted where the slow motion drive would normally fit. Also a key jack is fitted where the morse key would normally go. More on these two modifications later...suffice to say this is a bespoke version the builder wants. Use locking washers on all the nuts/bolts to make sure they do not come undone. Where this cannot be done use some varnish on the thread which will lock the nut/bolt thread when it dries.

Look at the photos to give you some idea of how the parts are fitted. Of course you will need to refer to the building instructions elsewhere on this web site (click below) when it comes to soldering in the components.

If you are sticking to the design shown there.... well follow the instructions carefully.

The hinge can be offered up to the cabinet and placed so the holes are centrally spaced about the centre line of the box. Mark the hinge for length, mark the hole positions and then cut the hinge and drill the holes. Remove all swarf. The hinge is best fitted with small rivets (as the picture shows) or if you cannot get rivets use round wire nails which can easily be cut to length and used as rivets.

Rivet heads will be flat inside the box when hammered down...and so they will not foul the chassis as you push it in the box. You will note the paper sticking out the box.....this is to prevent the screw heads from damaging the paint on the chassis whilst I try the "fit".....

Here you can see the receiver coil hanging up drying as it has been painted with varnish to fix the windings.

Drill pairs of small holes in the former to pass the wire through as this will stop the coil from un-winding! Plastic coil former, close wound turns and this coil is similar to the original.

Note the turns start from left and wind to right.

As you can see in the picture are from the left 5 turns and tap, another 3 turns and tap and then 33 turns to the end.

This produced a coil going from 8 to 3.3 MHz. The high end frequency limit is determined by your circuit's stray capacity and so it will vary. The low end limit is determined by your tuning capacitor's maximum capacity.

This is quite normal.

If you are going to follow the circuit we use then don't forget to follow the instructions elsewhere on the web site by clicking on this link.

The coil fitted here needed just such a hole drilled. The position of the coil, once establishing it would fit, in is marked, drilled, swarf removed and the coil fitted. See the photo.

You will also notice that I have started to fit some of the wires but only the earth connections to the tuning capacitors....and in very stout wire indeed. We don't want these wires moving about or the receive frequency might start to wobble!!

See the picture.

DISCLAIMER

As we have no control over your build, whilst we are happy to try to answer your questions, responsibility of the build is yours, as are precautions regarding HIGH VOLTAGES such as are necessary with valve equipment. If you have any doubt in your ability to safely construct a Valve Rig, then we humbly suggest you take a look at the Transistor Paraset.

These pages show the order of assembly of the components

Then also have a look at the pictures below to have an enhanced idea of what you could achieve.

Here are some photos of the paraset so far.

A couple of minor changes have been made to the layout for experimental purposes and you may spot these.

One in particular can be seen easily. Look for the small copper plate fitted to the tank tuning capacitor. This is a home made 100pF capacitor, the one that is switched across the tank to get a lower tuning range on the transmitter. In normal use this capacitor is "stressed" so a home made one of double sided copper pcb is being tried here. This should never fail! You will also see I came across a really good quality R.F.Choke for the PA so I used it!

In some places I used two components in parallel to get the right value so don't worry if you see too many components!

The tank coil has to be made now when I can find some tube to make it from.

This coil assembly will probably be made from the tube that aluminium cooking foil comes on. It will be soaked in varnish and allowed to dry hard before working on it to make the coil..

Paraset knobs Bukgin Type K94

Look at the top of this page for more details

The picture shows the inside of the box

There is no secret to riveting. However a couple of pointers might help:

1

Countersink the holes (a drill for this is perfect) on the inside of the box and lid so that the splayed rivet material has somewhere to go. This will enable you bash the rivets flush to the surface which is something you want. Think about it!!

Use copper rivets as they deform easily. Steel ones do as well so if that is all you can get use them. If all else fails try using some round wire nails. They too will rivet over if you hit them with a hammer.

3

Try a practice run of riveting. Rivets are cheap.......paraset boxes with all that metalworking working involved are not cheap!

The picture shows the outside of the box

Here you can see the tank coil has been wound and fitted to the chassis on a small insulating stand off. This allows one room to fit the coil as space is at a premium. The Tank coil is 18 turns of large wire if you have it (as per original....but this is not critical) if not use what you have available. The Antenna coil is 22 turns of slightly smaller wire....again this is not critical but looks more the part...but other wise use what you have available.

Drill the mounting hole in the tank former after you have wound the coils. Once wound and varnished several times offer the coil up to the chassis and then making sure it fits in mark and drill the mounting hole in the chassis front panel DON'T SCRATCH THE PAINT!

Secure the coil, and then varnish the nut and bolt so they cannot inadvertently come un-done. Actually I varnish all my nuts and bolts at the end to finish off. makes a nice job.

Look at the photos for guidance.

Now you can see the painted "cash box" paraset completed. It needs a dial, which as yet I do not have but live in hope of finding one. The valves are coming in the post. When the valves arrive I shall fit the spring clips to hold them in the lid properly. It will then be possible to test this replica paraset. I already have the power supply working from 12V D.C. using the circuit from this web site, ready and waiting.

Click here for link to power supply

You can see by looking at the dates put on by the web-master how long it has taken. The metal work for the complete box and chassis were laser cut from files downloaded from this web-site. Now you can see for yourself the standard of replica paraset that can be built, using our laser cut files in only a few days. The pictures show the paraset and below its 12V D.C. power supply.

Have a go yourself and if stuck for metal work we might be able to help...look elsewhere on this site. Certainly if you have a problem...send it to us by email and we will endeavour to reply with some suggestions to put it right.

When it is tested, details will be put here to finish the diary of the building of a replica paraset.

This is the chart for inside the lid which is as near an original as we can get !!!

Overall dimensions are 108mm long  by 70.5mm wide.

To use the graphic

1. Right Click on it and
2. use "SAVE as ..", and
3. save it in the usual way.

When the file is opened in say "Paint Shop Pro" you can check the size, adjust as needed, colour it if you like (HTML colour code #F7CB55 looks nice) and then print it off!

This appears to be an aluminium stamping with the number added after the stamping. The recess is painted black and it is held in place with rivets probably also aluminium.

The type style is apparently Gill Sans MT which has also been used in this section.

The length of the part we estimate at 38mm and width 11.5mm

The receiver did not work too well, the reaction was very fierce. The problem was caused by me missing out the resistor in series with the reaction pot. Once I fitted the resistor the reaction was working well. The receiver coverage was slightly too low in that it tuned from 7.1 to 3.2MHz. This was cured by removing two turns from the top of the receiver coil. This was carried out with the coil in-situ and the top of the winding re-varnished.

The transmitter did not work at all. Why.....I forgot to connect the anode of the 6V6 to the tank coil. It still didn't work. I had fitted an 82pF across the cathode rf choke (it was the one I came across first in the junk box) but it turned out this was just a little too small in value and was replaced by a 120pF and all is well with the transmitter now.

The dial arrived at last thanks to a kind offer and so now the paraset has been calibrated.

It was my original intention to try and use the paraset with its normal receive coverage of roughly 3.3 to 7.4MHz. But like this the receiver does not give of it best as the L to C ratio of the receiver tuned circuit is optimized for best performance. Remember I want to use this little rig and have lots of contacts. The receiver MUST hold its own on a ham band. Having listened to it there was only going to be one outcome. It had to be band-spread on 80m and the L to C ratio of the coil needed to be changed.

If you are patient enough and follow the instructions you can achieve results like the picture indicates. A nice straight line tuning characteristic. If you think this is good...then wait till you try the receiver as the change in LC ratio to achieve this tuning characteristic makes the reaction easier to use.

To test the transmitter I short out the antenna socket to the earth one and key the transmitter. Both bulbs should light up well if all is ok. All I need now are the correct knobs for the controls and my paraset a Whaddon MkVII/2 is finished! Well what are you waiting for!!