PYE 25C

[Refugee]

I am thinking that there would have been an armature that may well have come adrift and stuck to one of the pole pieces. Perhaps it is still there.

[pwdrive]

The adjusting screw probably set whatever was poking through that slot, as you say, might have come adrift.

Lawrence.

[trev757]

                                    Dear all

Many thanks for the replies. I have added some more photos to show the individual bits.

The construction starts off with the black 4 arm frame. Onto this is mounted a brass block which is held to the black frame with two screws with springs on them. There is then a centre screw, also with a spring, in the centre of the brass block. This screw pokes out through the centre of the speaker grille on the front of the cabinet, so is obviously meant to be user adjustable. As this screw in the middle of the brass block is turned, it moves the plate with the letter box hole (notice it widens out on the underside), and the coils mounted on it, nearer or further away from the copper coloured strip with the thread in it which goes to the centre of the cone. The screws holding the letter box hole/coil plate also fix the horseshoe magnet in place. One interesting thing I have just noticed in taking the latest photographs is that one side of the brass block has a + sign on it. Could this be to ensure the magnet is fitted the correct way up? I have also attached a photo of the underside of the copper coloured strip with the thread on it. Maybe something could have been attached there to go into the letter box shape hole, but I can't see any obvious way it would have been fixed. I don't know what these "reeds" look like anyway. When the coil/letter box plate is moved up towards the copper strip it magnetically attracts the strip very strongly.

I hope this helps to shed some light on things. There is audio getting to the coils by the way.

Thanks

Trev

[Refugee]

It looks even more like there should be a little steel flag that reaches into the letterbox shaped gap that is missing and may have been in the bottom of the cabinet so if you keep odd little things you find in the dust you may be lucky.

[pwdrive]

The latest photo's are interesting Trev, when I saw the first set you posted showing the slot only from the top I thought that there might have been an adjustable pole piece that poked up through it that was missing.
Having now seen the rest of the innards I cannot see were it would have been attached to the screw adjusting mechanism, so it might be that nothing is missing? The fact that the slot is tapered is also interesting and I am wondering if it is shaped like that to concentrate the magnetic field from the permanent magnet in the area of the reed.

You seem to have established that there is plenty of attraction between the pole piece and the reed, it's important that the reed does not have any contact with anything except at it's two fixing points and the rod to cone fixing point.

As for the other two screws with the springs that secure the brass plate/block to the main frame then they might be adjustable, possibly adjusting the tilt of the assembly with respect to the reed, the face of the pole piece (the one with the slot) needs to be parallel with the underside face of the reed and adjusted as close as possible to the reed without any physical contact between the two, the reed needs to vibrate freely.

Lawrence.

[Radio Fixer]

I think there should be a steel pole piece between the coils. Well there is bar that goes across.

Here is a pic of a Gecophone motor fitted to a Stork speaker restored by me.

   

Edit by me to remove reference to a magnet, that is there in the shape of the horse shoe.

Gary

[Refugee]

The pictures look like the cone to motor drive spindle has been adjusted by a twiddler so that the steel or magnetic flag has been pushed off the end and has then got lost.
The field concentrator will produce its strength across the gap and it will be stronger where it is narrow.
I am pretty sure there must be something projecting down there.
Try introducing a bit of steel with a sheet of cardboard fixed to the other end with a signal applied to the coils and see/hear what is happening.

[Radio Fixer]

Yes! with you Refugee. In the Gecophone design the horse shoe magnet concentrates flux into steel pole pieces and the plain steel blade, attached to the cone is attracted and repelled by the flux in the coils.

It looks as if in this design the horse you magnet (put a 'keeper' on this whilst disassembled) concentrates flux into the bar with the rectangular cut out. Into this as suggested by you goes a steel flag at right angles to the blade that has the cone connected to it.

Gary

[pwdrive]

You might be able to get an idea if something is missing by setting the user adjustment screw to the midway position then see what size gap you have between the underneath of the reed and the slotted pole piece, I would have thought that it was designed so when the adjustment is in mid position the gap would have been approaching it's ideal distance.

Lawrence.

[Refugee]

It looks like the user screw adjusts a static magnetic bias and that audio in the coils drives the flag to move the cone by adding or subtracting from the bias.