Dansette 1960s pickup

out.

is

Let this be a lesson to anyone in the UK - DO NOT store Rochelle crystal cartridges in lofts or sheds. The crystal must be hygroscopic. After removing the copper rivits (used flute section of small end mill to avoid the rotating rivet problem with drilling out rivets in plastic) and separating the 2 main parts, the problem was obvious. I just managed to move the parts apart enough to photograph before the active part fell to bits, lightly probing with a pin it was the consistency of dusty paste. (1 mm graph paper)

Left section is the cover, slid sideways, and the R section, on a nylon nut for focus, is inverted, part of the "crystal" with angled ground strip that touches the central pu pin (common to the other pu) to the outside, along with the signal pin for that pick up. The other pickup , not seen yet, but will be the same state, is under the central view. The brown part is the rubbery material that engages with the crystals and stylus shafts. Plenty of copper carbonate corrosion inside.

The remaining parts of the yoke, styli etc

Anyone reckon I can rob the crystal from a piezo ceramic pickup to fudge a functional and "as original" repair? I assume piezo-ceramic is not prone to this problem over 40 years.

--
Diverse Devices, Southampton, England 
electronic hints and repair briefs , schematics/manuals list on 
http://home.graffiti.net/diverse:graffiti.net/

FWIW, I have seen a number of grow-your-own Rochelle salt crystal experiments on the web; the process seems rather straightforward and the results look good if the work is performed with care. If you were successful with this cartridge and posted your work I'm sure it would attract a lot of attention :-)

Regards,

Michael

As I recall, ceramic cartridges do not have anything like as much output as a genuine crystal type. Why not just replace the whole cartridge with an SX5H or whatever ? I seem to think that Dansettes were fitted with a comparitively 'modern' type such as this, anyway.

Arfa

a

I reckon it is possible to convert piezo cartridges. I have dozens of later N.O.S Sonotone mono pickups, but have never looked inside one.

The central image is the active section. Not obvious in pic but the 2 vertical sections are each metal/piezo-ceramic/metal sandwich like bi-metal strip in fabrication, set in quadrature, so a pair of pickups, but electrically combined for mono output. So although these are pinned out as mono, just rewiring the innards and adding a pin would presumably convert to stereo. Electrical contacts are via fine sprung strips set in a black rubber pad like the white one shown, there is also another such black block removed, they hold in place in the casing. The lower creamish joining part is the plastic cradle/saddle for the stylus shaft. Cutting down the rubber pads a bit and sorting out some contacts and gluing in the ful-fi casing will probably work, whether capacitance etc is wrong I'll wait and see.

The kid's clothes peg, 1 inch long was just right as an insulated clip to hold a pair of contacts, temporarily, to check on a scope.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

fudge

bi-metal

stylus

gluing

I did not note how the 3 little silver springs were connected to the Sonotone active elements, I lost one in removing. As 3, I assume they were connected in series for mono output. But would they have been like to like or opposite faces connected between the 2 sensors, One of them is dye spotted red so there may be a difference in fabrication . Any opinions for ew-wiring, ie could go parallel .

Assembled new elements in the old casing but will wire up with silvered wire tomorrow as I've done enough working under a magnifying lamp today.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

ISTR that cheap record players that just had a single valve output stage and no pre-amplifier used a "High-output" cartridge. (Is that what the H in SX5H means ?) a standard output cartridge would be very quiet and a ceramic quieter still.

Also FWIR that output valve would typically be a UL84 or similar (not as a rule EL84), with 100ma (80v) heaters fed off a tap on the shaded pole turntable motor, to save the cost of a filament transformer.

The crystal cartridges didn't need any excitation voltage.

DG

funnily enough this came up just a couple of days back here:

to be honest I wouldn't mess about rebuilding a cartridge this common and low cost unless you have lots of time and patience on your hands. It would be simpler to get a NOS stock TC8 turnover cartridge off ebay if you want the orignal look rather than functionality, or even better, fit a slightly more recent stereo-compatible cart like a BSR x5H (has output which matches the crystal carts) which will enable safe playback of stereo records. these are widely available on the 'bay for low cost and the main advantage over your original turnover cart is the turntable can play all kinds of records.

-B

Yes Derek, that's it exactly. I did one just last week that used a UL84 and UY85 reccy, fed just as you say, by a tap on the motor winding. I seem to recall that those crystal cartridges had an output approaching 2v p-p, and obviously, with a very high impedance in the order of megs, which matched nicely for level and Z, directly to the grid circuit of the UL84. Ceramic cartridges, on the other hand, only have an output of 200 mV or so I think, at an impedance of around 50 - 100k. I think that you are right that the "H" is for high. The BSR SC5H is a high output ceramic, so I guess it's "S" for stereo, "X" for xtal, "C" for ceramic, and "H" for high.

It's all going back a bit to my apprentice years now, but I have a dim recollection of later units that were fitted with a ceramic cartridge, using something like a UCL84 which contained a triode as well as the output pentode, and that the triode was pressed into service as a preamp.

Arfa

fudge

and

think,

"H"

for

using

The circuit is minimalism, as in the Newnes 1959 guide for Dansette Major de Luxe. A triple cap can, 2 other axial caps, 2 Rs, rectifier , 2 pots, EL84, mains and o/p transformer. I took another Sonotone apart. I had not lost a silver spring from the other one, only one active element is used so 2 wires only. I will try lashups as series and parallel trying to determine which gives most signal/ most f range.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I decided to take a skew view before wiring in

2 rings of green silicone rubber sleeving to take silvered wires before dabs of gummy glue. One black rubber pad chamfered to rest in the top cover, yellow-white rubber pad cut down , orginal brown rubbery moulding that enclosed both original rochelle crystals and extensions to both stylii saddles. The saphire of the original remounted ( coded yellow and green) stylus is just visible to the top and right of the brown section, through a gap in the white plastic casing. The original small plastic stylus saddle went quite neatly through the hole for the original rochelle. The now unused second brass screw mount for the other stylus and its corresponding saddle rest flat, on the brown section, is visible on the lower edge. Decided to wire in only one active element of the Sonotone and also to have more space to play with ditch the 78 option and just use 2 of the original 3 pins and plates to the outside. It is very critical on signal generation on how much the rubber supports are compressed, I may cut the thickness down a bit if the sound is ropey. It would probably be possible, in space terms, to separate the 2 sonotone and mount one either side and retain double stylus, rotating function.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I wish I could make enough money in the repair business, to have time to 'play' like this ... !! d;~}

Arfa

original

is

original

generation

down

sonotone

Googling for what a Rochellle crystal should look like I found someone else has gone down this route

completely different internals

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

dabs

rubber

the

hole

have

3

on

a

Got back to this back-burner job today. I had to abandon putting piezo element in the original cartridge housing, not enough output. Sliding a cable tie lightly over the stylus gave about 100mV , wheras doing the same over a complete piezo, ie vibration not having to go through a load of brownish rubber gave about 2V pk-pk output with the cable tie. Adabted the yoke to be able to slide in piezo pick-up ,retains the little

78/LP flag , and can rotate but no second stylus, and is shrouded in the arm so nothing shows in normal use.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on