PYE 25C

[Radio Fixer]

Seems plausible to me. Complicated compared to the Gecophone arrangement with its perfectly flat blade.

Would have thought there ought to be some witness marks ...

Gary

[Radio Fixer]

Here is an explanation of how these speakers work, this one being the RCA 103 Model. It may not be of interest so if not just pass on by.

I can no longer find a Web site for Kris Walter but these I grabbed back in 2005. He was actually selling a Radiola 60 with it and I think they were part of the advert. We had a few e-mail chats and he came across as a very learned guy. His site had beautiful animations all done by him.

I tried to add a Word.doc decode of the explanation but couldn't seem to do that? So here it is copied below:



GNT write up of the Kris Walter explanation of how the RCA 103 Speaker works



Here is how a family of 100 RCA speakers works. (see figure).

Let's refer to a cartesian coordinate sysem with x-axis pointing right, y-axis pointing up and z-axis
pointing towards you.

Position a horseshoe permanent magnet such that its south pole rests on the positive x-axis and it's
north pole on the negative x-axis, the arc pointing in the Z direction.

Shims guide the magnetic field such that Its north-south direction points along the positive y-axis at the
origin of the coordinate system.

Centered and suspended at the origin is the (ferromagnetic) armature, which can rotate around the x-axis.

Also centered at the origin and coaxial with the z-axis is the speaker driver coil, which is connected
through a filter coil and a cable to the amplifier.

The alternating current in this coil produces an alternating magnetic field along its axis, that is along the
z-axis and induces magnetism along the armature.

A positive driver current may produce a south-pole at the front (+z) end of the armature and a north-pole
at the back (-z) end.

The front-end south-pole is attracted by the north shim and repelled by the south shim, thus moving
Downwards in a negative y-direction, whereas the back-end north-pole is moving upwards, doubling the
torque.

A rod soldered to the back end of the armature is connected to a leaf spring, which in turn is connected
through another rod to the back end of the speaker cone, generating some leverage effect.

All movements reverse, when the current through the driver coil changes sign.


Gary

[pwdrive]

The question is what's the fix, it's not known for sure what the missing bit looked like if there was one, the idea I put forward in the drawing is only a suggestion.

Another question is should it work as is when reassembled, if the gap was set close I would have thought some sound would come out of it.

Lawrence.

[Radio Fixer]

Even if the lost part is fabricated will it work satisfactorily ? Perhaps not.

These sort of speakers come up regularly at swaps so changing it out might be the best way.

[pwdrive]

Thanks for the description Gary, yes, that's a balanced pivoted armature driver.

So far as I can make out there were two basic reed types, one where the reed was only fixed at one end and the other where the reed was fixed at both ends like Trevs speaker.

Lawrence.