[sdiy] How do reverb tanks work?

[RMC]

Hello

I'm interested in spring lines and most specifically, the transducers used. 
Does anyone know the detail of how the output transducer works?


The input transducer uses the motor principle to develop torque which 
imparts torsion to the spring, but how does the output element work?

Having just dismantled and repaired a broken springline (the output 
transducer coil had gone open circuit where the lead-out flex solders to the 
coil turns, due to 1970s corrosive flux!), I can't understand with certainty 
how it works.

The ends of the spring seem to have tiny ferrite beads mounted on them, 
which are lined up to occupy an air gap in the output transducer. Either 
that, or they're magnets.

In the former case the gap reluctance presumably gets modulated by movement 
of the ferrite bead. In the latter case, an MMF gets generated by the 
magnetic flux cutting the core (aluminium laminations??) and hence inducing 
a current in the output coil which is common to the magnetic circuit thus 
formed.  As far as I can tell, the circuit that receives the tank output 
doesn't provide a constant current through the coil so there isn't a method 
of detecting the relucatnce - it must be that the little beads are magnets. 
Is it true?

I managed to leave out a couple of tiny little brittle black (plastic?) 
"plugs" which appeared to act as some kind of spring damper, where the 
spring end feeds into a tube, where it gets anchored. This is after it has 
passed through the output trasnducer. However, it works without these 
components (which shattered, hence why they're not re-fitted).

There are a load of picrues on my website - which the ISP has just shut down 
because I exceeded my storage allowance. I'll post a link if I get that 
problem resolved.

Cheers

RMC, England