Wednesday, April 23, 2014

Parlophone Parvus Plays

The soundbox is now decent, but not quite on the acoustic quality level it could be. Some of the parts are made of zamak, like many of these reproducers. The material is ideal for such small parts; easily molded with good accuracies and nice smooth finish. A drawback is that over decades it corrodes from the inside and the whole part swells. It can become as brittle as a dried-out sandcastle.

This soundbox was not quite that bad, but a lug of the pivot-cover did break off in my hands by just touching it. Replacing the gaskets that hold the diaphragm was something I did not dare to attempt. The gaskets are hard, but have glued themselves to the metal in some places. The ring already showed cracks on the outside, so the risk of the ring totally breaking apart is just too high.

Carefully taking it only partially apart and gently cleaning and painting does make it look much better again though. With the cleaning, the pivot should be a bit better also.

With a new gasket on the flange that fits in the tone arm it does look the part again. Even though it's a bit lacking in treble and more 'buzz' risk on loud parts than it should have. It is however freely moving and will not damage records unduly.

Now the brake still needs some seeing to, but otherwise it is getting there. Definitely not as new; it has plenty of scuffs and marks and looks its age, but again the Parvus is a very neat and usable compact portable gramophone.


Friday, April 18, 2014

Paper Page Gauge

A while ago I spotted something like this in an old magazine. Can't find the article or magazine back again, but it set me thinking that this would be a neat thing and quite practical to make.

An experienced typist would have no need for such a thing, but I'm not an experienced typist. This does actually help getting a feel for how far along the page I am and how many lines still to go.

The magazine picture that got me the idea was from the late thirties. Scouting around a little, this was an extra feature of a carbon paper holder. A few patents were published around that time detailing this paper page gauge, e.g. US2082494 - 'Backing sheet for manifolding assemblies', US2088039 - 'Sheet aligning and gauging device' or US3842506 - 'Spacing means and method for typing paper'.

My own page gauge (sans carbon) is designed to suit DIN A4 paper (I'm on the continent...), so must be printed on a larger than A4 sheet of paper. To make your own, this PDF file is made to print on an A3 printer. Then with some cutting and pasting (the actual, not the virtual) it'll become a basic paper page gauge.

To edit and adapt to taste or paper size, here it is also in EPS format that should load in most vector graphics editing software.

Curious if/how anybody finds this in use and what changes and improvements can be made.

Thursday, April 10, 2014

Parvus Mechanism

The complete mechanism of the Parlophone Parvus portable gramophone is again mounted on the deck. Newly painted the deck and all parts polished and fitted again. The whole assembly dropped back in the case and fixed with 12 screws all around.

The side-view of the bare deck assembly nicely shows how the motor is in one part of the case and the whole acoustic part in the other half of the box. The tone-arm connects to a fairly basic and short horn. That horn projects against the divider plank in the box to project the sound backwards (and somehow out of the opening in the deck of the gramophone). It also shows the how thin the sheet-metal deck really is. Flimsy even.

The Odeon motor looked fine as it was. Didn't spot a type number, but it does have the Odeon logo, Odeon also being part of the Lindström group of companies. Luckily the spring seems to be fine, locked in a closed drum. Even though the grease in the motor is old and will be a bit hard, a full winding still plays a 12" record. So I'll not be taking this motor apart quite yet, certainly not messing with the spring drum for now.

The friction pad of the regulator was hard like a stone and quickly replaced by a small square of leather cut from an old belt. This pad is held in a U-bend that is easily pried open and bent closed again with pliers. After fitting the new pad, apply liberal amount of machine oil. (When first spinning the motor again, be aware that the friction disk is going to spin around some excess oil as the pad touches it...)

This motor has a very handy speed adjustment lever arrangement, located around the spindle. Calibrating this motor to play at 78 with the lever in the centre position is relatively easy. After setting the motor to 78 with the lever, loosening the clamping screw that locks the lever to the adjustment bush allows you to easily move the lever to the middle position of the scale. Very visible technology. (On the HMV portable this adjustment is much more of a trial and error process.)

Originally the motor was mounted with rubber washers, pulled up against the deck. These had turned to crumbly stone and a set of hex nuts now act as spacers. The way the rubber was mounted with the motor still pulled it metal on metal, I can't yet figure out why rubber was used at all. It cannot have been very useful in damping the motor sound transmitting via the deck. Maybe I will fit new proper rubber washers one day and figure it out.

The semi-automatic brake took some tweaking to make work again. The position of the brake rubber relative to the turntable inner rim is the critical alignment. When off, it should run clear of the rim always, but when the brake is engaged it must press with enough force to hold the turntable against a fully wound motor without slipping.

Ergo the Parvus is getting there. The soundbox is next to be tackled, but the gramophone already looks quite good and it even plays again!

Saturday, April 5, 2014

Printed Parvus Part

The one missing part was the flange of the winding opening in the front of the case. This flange or escutcheon not only protects the hole but also lends support to the handle during winding. The original part perhaps buckled and broke from the repeated circling load stress. Probably was made of stamped thin sheet metal.

The outline of the original part could still be seen on the outer case, a slight imprint and a different color of the leathercloth where it was protected by the flange (at least for the first part of its life). Using this outline and taking some guesses on likely dimensions, a new part was modeled in 3D that would be suitable for printing. For this I used the free to use Sketchup Maker version. It takes some getting used to, as far as I can tell it is a quite powerful 3D engine with relatively limited and simple editing tools on top.

The maker version of Sketchup has only a few file format options, but the model can be exported as a Collada 3D file (.dae file). As advised by Shapeways, this Collada file can then be loaded in the (free) Meshlab tool. This tool is all about the mesh and it offers many functions for inspecting or fixing the mesh. Having taken some care to have a closed model in Sketchup, steered well clear of all that and just exported the part as an STL file suitable for the 3D print shop.

Not being all that sure of the dimensions and proper fit, ordering it right away in metal seemed a step too far. Settled for the regular black plastic version, much cheaper and easier to drill and file to size. Arrived in due time and looked very clean and of course 'sandy'. As they explain very clearly, the Nylon part is made on an SLS machine so consists of lots of small plastic spheres that are laser-fuzed together. This also means that sanding a surface will not yield a smooth finish - just more 'sand'.

When painting the part, the first layer (or two) get sucked into the part. This probably has as side-effect that the part gets quite a bit stronger, as the fuzed spheres are now held more rigidly under load. It actually took 3 layers of paint (and some sanding in between) to get a decent looking part.

Unfortunately I got the pitch diameter of the screws slightly too small, so carefully drilling the holes larger was needed to get a good fit. During fitting to the case, one of the holes in the case needed to be re-drilled. Otherwise it fits very snuggly in the slanted winding hole.

The central winding hole diameter could have been a bit smaller, to be a closer fit with the winding handle. Then it would flex a bit less when winding the spring, but it gives decent support as it is now.

All in all a reasonable replacement part. Now that I've made and fitted this one, I know how to modify the holes (make them slots) for a better fit. Also the flange could be designed a bit different to match the clasp a bit better. But for now I'll stick with this one. (Until it breaks, of course. Then we just print and paint another one... ;)

We'll see how it holds up, but 3D printing seems a viable route for replacement parts :-)

Tuesday, April 1, 2014

Recovering Parvus

Amazing the difference new turntable cloth covering makes.

Compared to the state it was in the case also looks a lot better now after some basic cleaning and a bit of polish. The metal fittings are cleaned (de-rusted) and painted and a new (old) handle picked up from the local shoe and leather repair shop is fitted. Some of the leathercloth (leatherette, rexine) had lifted from moisture in much the same way that typewriter cases suffer this. That is now mostly glued down and flat again, well it is flatter at least. Like the portable's cases, used diluted PVA glue with a drop of dishwashing liquid to make it flow easily, then press down by a plastic bag with sand or fine grit on top of it to let it dry overnight.

It's still missing a flange for the front winding opening, but that should arrive later this week from the printers.

The logo on the inside record-tray got slightly damaged where it is pushed up by the turntable spindle as you close the lid. The top swirl of the Carl Lindström £ took some damage, otherwise still very presentable and colorful.

Even though it proudly proclaims that it is warranted best German manufacture, the Parvus decal got put on a bit askew. Small detail, but still...

Overall it is recovering nicely :-)