BSR Factory Workers: reaching out..

[_Cosmic_]

Originally Posted by Hartley118

I'm sure that it's worth pursuing this project further: the fact that you've already achieved a voltage output is very impressive. Hoping to reproduce the performance of a TC8H cartridge without all those years of painstaking development from BSR, and before them Cosmocord, Astatic, Brush et al may be a bit ambitious.

AFAIK, a Rochelle salt sensor is different from a ceramic piezo element in that it doesn't need 'poling' - the piezo equivalent of magnetising a magnet, requiring a strong electric field to be applied to the element to align the 'cells'. A Rochelle salt element on the other hand needs no poling because its crystal cells are pre-aligned in the crystal structure, implying that a single crystal should give the biggest piezo effect. A rather rapid crystal growing process is likely to produce a complex structure with the big crystal actually containing multiple internal crystal boundaries which upsets the cell alignment and probably reducing the piezo effect.

So it's probably worth testing a number of your crystals. The smaller ones may be more effective than the bigger ones because they have a more regular structure.

Of course it goes without saying the the crystal needs to be perfectly dry: any water that isn't locked into the crystal structure will load the output signal.

Martin

Yes Martin thanks for that. I think Brush were probably the original creators of the Crystal elements, I think Sonotone (hearing aids) used their technical knowhow at their factory.

My crystals have been growing slowly over 3 weeks now at about 15C degrees. When they get larger they do look a bit flawed. I might make another batch and try to purify them an extra couple more times.

From my research I believe that a seed crystal was placed in the rocking tank and a super large rock was grown, probs about 20cm x 5cm ( just guessing the size). It was then cut into slices.

Unless they were designed to be thinner at the mount ends, the slices were 1mm thick to fit into the flexible mounts. This is rather like the next generation ceramic elements looked like.

When growing a small crystal of 16mm length the width is naturally about 3mm so I have to reduce this down to 1mm by sanding.

I'll keep going for a while until I run out of ideas, which could be quite soon!
Meanwhile I will do some tests on the smaller crystals as you suggested.

Thanks so much for posting, it's much appreciated.

[bluepilot]

Originally Posted by _Cosmic_

I'll keep going for a while until I run out of ideas, which could be quite soon!

Apologies if this has been mentioned before but there's a lot of thread to read through so I may have missed something. Are you sure you're using the correct chemicals? It's mentioned here that cheap cream of tartar may be something else which won't work.

[_Cosmic_]

Originally Posted by bluepilot

Apologies if this has been mentioned before but there's a lot of thread to read through so I may have missed something. Are you sure you're using the correct chemicals? It's mentioned here that cheap cream of tartar may be something else which won't work.

Hi Stuart.
Yes I've seen Rimstar.
Thing is, on the video he is whacking that largish crystal and only producing 2V peak. That amount of force would obliterate one designed for a pickup wouldn't it.
The size we need for the cartridge is only 16mm x 5mm x 1mm.

As regarding purity. I'm using sodium carbonate powder thus removing the drying step.
You can buy the Rochelle salt chemical, Sodium potassium tartrate (KNaC4H4O6·4H2O), ready made but its expensive. This might be my next step as it negates the purity problem doesn't it.

[Trevor]

is the output a xtal orientation thing is the crystal cut or ground in the correct direction
I am following this with great interest ! You would have thought this technology would have been well worked out by now millions of units having been made
Trev

[_Cosmic_]

Originally Posted by Trevor

is the output a xtal orientation thing is the crystal cut or ground in the correct direction
I am following this with great interest ! You would have thought this technology would have been well worked out by now millions of units having been made
Trev

Hi Trev
I know, it's a complete mystery isn't it.

I'm sure I can find out exactly how it was done but it's going to take quite a while researching on espacenet as all the copyrights should still exist on that achieve. I mentioned it earlier in the thread. That's how I discovered the rocking tank process.

Yes, the orientation does make a difference when using quartz slices for radio oscillators (see post Crystals go to War post earlier). For maximum output they have to be cut at 45 degree angle to the Y-axis I think it is. Apparently they were cut with a "bandsaw" but the Rochelle crystal is a bit crumbly and most of mine would be too small for that so I sand them down to 1mm. Plus, the crystals would have to be a bit larger to cut to orientation. I will probably try that soon.
According to the archives Rochelle crystal can be used in pickup cartridges in same orientation as the crystal grows (as sheer plates) (mentioned in a previous post).

[John10b]

I wonder if you spoke to the local newspaper editor if he would put a small article about bsr. Only a thought.
John

[_Cosmic_]

Just an update folks...
I've found out some more about the methods of making Rochelle salt crystal cartridge elements.

Most of this latest information is from patent papers filed by The Brush development Company in the 1930's.

Once the slabs of crystal were produced, by the methods described in previous posts, they were either used singularly or 'cemented' together in opposing directions to form a dual unit and these further 'cemented together to form larger units. The electrodes were then 'cemented' directly to the surfaces.

Here lies the problem.
It was found to be 'essential' that the crystal plates (produced by band-sawing from the slab) were extremely thin. They are quoted by Brush Dev. to be 0.003-0.004 inch and that is 0.07-0.01 mm which seems pretty hard to believe.
Because of the fragility problem of handling, attaching electrodes and cementing two together to make a unit with opposing forces, a method was invented to enable this to be accomplished as follows:

A slightly thicker crystal plate than finally needed was attached to a non-conductive supporting surface of similar. This process created a 'unit'. This enabled the unit to be handled and the electrodes attached without fracturing the crystal plate/element.

The use of a lathe cutter rotating at "2000 feet per minute".
The crystal units were loaded (adhered) onto a vertical turning disc with a raised rim to stop the units spinning off the disc. Crystal units were placed into receptacles and held in position either by one of 2 methods.

Either by atmospheric pressure acting down on the crystal surface aided via vacuum from under the units, or held in place by an adhesive compound made from "5 parts vaseline, 2 parts paraffine, 1 part rosin".
The cutter (adjusted more acutely than for normal cutting operations due to ease of cutting) passed either from centre to periphery or started vice versa.
On one pass of the cutter a known amount of width was removed and the process repeated until the desired thickness was achieved.

If producing a twin crystal unit, the unit was then removed, turned over, remounted and the other face reduced to the same thickness.

Producing crystal elements in this way made it commercially viable without so many losses due to handling, attaching electrodes and cementing opposing plates together.
Thinness of "two and one half to three thousandths of an inch" (0.08mm) was consistently attained within very strict limits.

The units were also later waterproofed, I will go into that later. Then the manufacturers needed to invent the stylus assembly! We are not concerned with that as we are trying to renovate cartridges that are functional apart from the crystal element.

WELL, where does that leave this project?
The next step is to cement one of my elements (made thinner than the 1mm I previously made) onto a non-conducting supporting surface and see how it responds.

I hope you are finding this as interesting as I have researching and experimenting.

[John10b]

Yes it is very interesting Chris and thank you for sharing this with us. It just shows how much went into the development and production of crystal cartridges all thoughts years ago.
I wonder how they make todays crystal cartridges?
John

[Trevor]

All done to produce a product that was to say at least very cheap a few quid at most !
this must have been a very repeatable process just look at todays piezo sounders pence each
Trev

[Refugee]

I would be tempted to try one of those 0.1uf brown ceramic "penny" capacitors.
Just bias it with a couple of volts and let the edge furthest from the leads rest on the stylus.