Wednesday, May 20, 2020

Recreating 1920s crystal-set wiring

Continuing the restoration of the 1923 Edison Bell crystal wireless set, the wiring needed to be re-created. The remnants of wiring in the set as it arrived was clearly not original - at some stage the original wiring had been modified to probably use a 'modern' diode roughly screwed to the roughly drilled extra holes in the baseplate. The old wiring and all the lamp-parts were likely removed to make space for this. The thin cotton-covered wire itself also looked incorrect - the length of PVC-insulated wire was certainly not original.

Even though there is not that much information on the inside of these Edison Bell sets, or even on 1920s crystal sets in general, some pictures could be found online that showed the inside wiring. These are of three different units, so that common features to these three are likely to be original factory fitted parts.

From these images, it becomes clear that the set was originally wired with 'thick' wire rod. This was actually quite common in 1920s radios and electrics; bare wire forming a neat three-dimensional circuit. From the pictures made a guess at the diameter (probably just over a mm) and got some tinned copper fuse wire of just over a mm diameter.

To straighten the thick wire ('rod' material, really); the regular procedure. Unwind and manually un-bend a length of the wire. Then clamp one end in a vise (or clamp to the bench-edge) and the other end in a drill. By pulling and then twisting the wire left and right it gets nicely straightened. A hand drill is good to use as it gives a bit of 'feel' for how you're deforming the wire and when to twist back. For safety, always keep a bit of tape over the wire ends (cut wire is rather sharp and springy...).

With needle-nose pliers and a bit of 4mm tubing as former, bent loops in the wire ends and made the sections to fit the terminal posts. The first leads to fit were the connections to the crystal detector - these must've been formed in-place, as they pass through the small hole in the base-plate and should have loops at both ends. The loops at the detector crystal-covers need some tweaking with a kink in the lead to clear the glass. (Suspect the original may have used slightly thinner gauge wire, or perhaps even not made a loop there at all - just a straight wire-end?)

Following the same procedure and consulting the reference images of original sets, the complete wiring could be recreated and fitted again. Also the leads to the slightly-different reproduction lamp-fitting was added.

Bringing the leads to the far end of the variometer seems a bit odd - reversing the variometer to have the terminals closer to the baseplate would've saved some copper. But perhaps the ease of fitting (or whim) was more important than a few inches of copper wire back in 1923.

With some thinner cotton-covered wire to the battery-compartment, the lamp again works too. (From the pictures it could be seen that this should also be thick 'wire' with a green insulating sleeve - but there's a limit to authenticity here, this is more practical.)


Sunday, May 10, 2020

Missing fittings and an assembly puzzle

Continuing the restoration of the Edison-Bell Type B crystal wireless set, a next step was to find replacements for the missing fittings. A British product of nearly a century ago, it naturally does not use any metric standard-size fasteners or fittings. This made it a bit of a puzzle to determine the right sizes - and then a puzzle how to get these today.

From playing with 1920s vintage Meccano (the Electrical Outfit), had learned that BA-threads were common in electrical equipment of the era. Checking with a Meccano part 304 (6BAx1/2" screw) confirmed that e.g. the mounting holes for the lamp in the panel were indeed 6BA. Measuring the remaining fittings on diameter and threads-per-inch confirmed all fittings to be 4, 5, and 6BA thread. (To measure t-p-i, firmly roll the screw in a bit of paper or cardboard to make clear marks and then measure ~10 marks to get the value.)

Again the internet-age allowed ordering of individual BA-sized brass screws and nuts. These duly arrived from Britain (despite current conditions!) and were quickly nickel-plated like the originals. One 4BA screw first had the cheesehead filed down to a flat top - from the tool-marks on the original contact-studs, this was exactly what the Edison-Bell must have done in 1923.

Now all fittings cleaned and missing fittings replaced by new - the panel looks very presentable again:

No more unsightly empty holes. Also underneath, the missing screws and nuts are added - more complete, but still without wiring. (The variometer is still assembled wrong in the below image - that one turned out to be quite the puzzle.)

The battery-studs and lamp-holder-screws are 6BA, the variometer fittings and mounting screws are all 5BA, as is the detector mounting screw. All terminals and studs are 4BA. (In case anyone has one of these radios and needs to replace a fitting.)

The variometer (or variator?) is a rather clever set of parts by Edison Bell - they also sold it separately for building into other sets and it can be assembled in several ways. The mounting brackets can e.g. be mounted any side - also it took me a while to work out the correct, intended assembly of the circuit for the coils.

Both the outer and the inner sphere have 48 windings, at ~65 and ~70mm diameter. These should be in series, allowing the centre sphere to rotate and work with or against the overall inductance. A surprising element (to me, at least) is how the outer shell coil-halves are connected. This is simply a pressing of the bare wire agains the small nut in the other half that clamps that other half's wire.

The two pivot bolts that hold the inner sphere are the leads into and out of its coil. The brackets on those bolts allow routing the circuit to the outer coil terminals. Took a bit of puzzling, this.

One other item was the dial scratching the panel. It turned out to not be warping of the dial (as originally suspected), but a manufacturing defect in the top knob. The middle insert-nut must have been placed slightly askew in the mould, before over-moulding. This was mitigated by shimming (waxed paper) between the top-knob and dial.

The markings in the dial were then re-done with white wax - following again the advice from the excellent book on typewriter repair by Teege.

Radio repair with thanks to the Typosphere and Georg Sommeregger :-)

Saturday, May 2, 2020

Obtaining obsolete accessories (B&L part nr. 31-59-59)

One of the entertaining challenges with obsolete technology can be finding the correct accessory or spare part. The item itself is long obsolete, the manufacturer no longer services the item (or more often the manufacturer is long defunct). However the digital age with the global flea-market that is the internet often helps out - if not available right away, then it's a matter of laying in wait for a time.

Sometimes on the other hand, you just stumble on an item by accident - as was the case with this accessory for my plain-stage Bausch & Lomb type H microscope. This microscope is the simpler (cheaper) version, catalogue number 31-21-50-08 with a plain stage priced at USD 135 back in 1935.  (Who at B&L came up with these type numbers? There probably is a logic there...)

(Catalogue image from scan at

To later add a mechanical stage to one of the lower-cost H microscopes, Bausch & Lomb sold attachable mechanical stages. These were available both with and without a graduated scale. Not a cheap item, either version. The graduated stage shown here in the 1940 catalogue for USD 33.

(Image also from the great library of B&L literature at

Purely by chance and not specifically searching for it, I spotted this B&L mechanical stage with graduated scale for sale online.

As it was offered for a reasonable amount, and the chances of the exactly-right accessory being available a next time being slim, went ahead and 'bought it now'. A rare item to find - Bausch & Lomb microscopes are relatively plentiful in North America, but in Europe they're uncommon. Specialised accessories more so. Even with international shipping (Portugal), it still came in reasonable at around 20 Euro.

It is of course 'vintage', so there's some play on the horizontal movement and the vertical-movement wheel is a bit bent (must have gotten a heft knock). But other than that, it is functional and complete with the thumbscrews to attach it to my plain-stage type H microscope.

So now a B&L type H fitted with the attachable mechanical stage.

The stage has straight-sided knurled knobs. From some scouting around and checking serial-numbers and images, it seems that in 1940 Bausch & Lomb changed their microscope knobs and wheels from double-knurled to straight. This makes this accessory indeed likely a 1940s item (still dimpled face to the wheels); a good match for the 1939 microscope.

Already used to chase pond-life around a slide - and neat to be able to add the accessory to this obsolete piece of technology. (I.e. entertainment for the 'completist' in me :)