Building Eric’s Mk-VII

The 25th of February 2019 I started the build of a Mk-VII Paraset, the wooden case model and a power supply, also in a wooden case, like in this photograph:

Gathering parts, in my case, is today not such a problem, as I can pick freely from the Paraset Warehouse. I agreed with Eric to make the outside of the Paraset looking more or less authentic, but use modern parts “under the hood”.

First thing to do was to countersink the water-jet cut holes in the factory made front panel:

cof

As you see, I clearly marked the holes that were NOT to be centered.

Next thing to do is to clear up the workbench in the garage, to make room for the spray-painting job. I will be preparing 3 front panels at the same time, to have a few painted panels on the shelf.


April 18, 2019. Finally! Temperature and moisture level in my garage are finally acceptable to spray paint the three panels I drilled earlier. They all got 3 coats of flat grey paint. I will leave them rest for a few days so the 2 component paint can harden.

Next thing to do is to put on the lettering. Or making the needed mechanical parts in the meantime. Phew! A lot to do, but great fun!


April 2, 2019. Some weeks ago I started the build of a new jig for modifying trimmer variable air capacitors into variable air capacitors with a shaft. The latter types are almost unable to find anymore. I had made a wooden jig before and that worked also, but had a few issues. So I made this:

To be able to see the adjusting of the vanes properly, I mounted an affordable digital microscope, that I can also use for other jobs that need magnification.

Next step is to take 3 varcaps apart and to cut off the extended bearing:

To the left, the original varcap without the blocking nut. In the middle the one with the cut off bearing. To the right the rotor and pressure spring.

Than, the varcap and its new shaft go in the jig and the vanes are adjusted. Than a hole through and through is drilled to receive the blocking pin, a 1,2 mm brass nail that is riveted. Below, the varcap in the jig. On the bottom you see the image of the vanes on the microscope screen.

And finally, after a while, you end up with the 3 variable air capacitors:


June 3, 2019. I have completed some more mechanical parts. From M12 bolts I made the bearing for the vernier drive. One starts with 5 of these:

….. and after sawing, and turning, they become like these:

Than drilling the hole for the shaft. First I used a 3 mm drill bit:

… and after that a 1/4 inch drill bit:

Resulting in 5 of these:

Now, that is only the bearing. Notice the hole is off centre. That is for adjusting the grip on the driver plate, under the dial. You will see that later.
Next is to make a shaft. On the next photo you see a piece of 40 mm brass rod, 1/4 inch diameter. In the middle the tapped bottom piece, to the right the untapped top piece.

I cut out of a piece of brass sheet, little square pieces. Square because that is easier to cut than round. The sheet has to remain flat, so need a hack saw to make it round. I made them round on the lathe.

When you assemble these parts, you will end up with 5 of these:

Finally I decided to cut the nuts in half. As sawing would be a tedious job, I used the angle grinder to take away about the half of the nut’s thickness. A finish in the lathe to make them properly flat did the rest.

Next thing to do is to make a mounting sheet for the 60 mH rf-choke. The Paraset used a type of choke that had 4 mounting holes. The modern chokes we can get our hands on, have only 2 holes, and these don’t correspond with the holes in the front panel. the solution to this problem is to make a fitting mounting sheet on which the choke is mounted. Here it is:

And here you see the parts put together:


June 7, 2019. Today I made the coils. I began with the raw formers and polished them. In the TX-coil I made groves to accommodate the 1 x windings for the light bulbs:

After that I put the windings on. Three sizes of wire are used. Last job is to cover the wires with varnish, to keep them in place and moisture out.


June 16, 2019. It is inevitable: the legend on the front panel is the next thing to do. After that, mounting of components can begin. So I laid yesterdays fake news on the table to work on, fetched a bowl of water and started cutting the text transfers. Now, you can’t draw pencil lines on the panel to align the text, it has to be done “at sight”. In the old days they used silk screen print, I guess.

The first three transfers I ruined. I had to get the hang of it, again. After those first three, it went all right and after a few hours I ended up with this:

Now I will let it dry over night and tomorrow I will put a few layers transparent varnish on the panel, to protect the transfers.


June 22, 2019. Time to mount the necessary hardware, like sockets and solder lugs and alike. I’ll have to wait before mounting the variable air capacitors, I have to find suitable knobs before knowing the length the shafts have to be cut.



July 13, 2019. Last few days I have been busy filling up the front panel with the last mechanical parts. Also soldered in some components and wiring. It is certainly going somewhere! The big empty space is where the TX coil will be fitted. The Rx coil is already in it’s place.

Let’s flip it around. The scale is a temporary one. It will be replaced by an original, later. The other knobs are at least 60 years old, from war production tuning boxes for the BC610 transmitter.