[sdiy] demagnetising spring reverbs

[James Dunn]

Hi list,

Some time ago I came across a suggestion to increase the signal to noise 
ratio in the ARP 2600 reverb unit by reducing the value of R273 by half. 
I tried this mod and it was indeed louder but after a while the reverb 
seemed to deteriorate. It now sounds very muddy and distorted. I looked 
at the signal being sent to the reverb tank on a scope and it was also 
distorted, although it only had a minor glitch when I disconnected the 
tank. So I concluded that the tank must be faulty (probably by 
overdriving it). This <http://sound.westhost.com/project34.htm> website 
would seem to confirm this - it says:

> ...but you must be very careful, because overdrive causes the small 
> pole piece to become magnetically saturated, leading to gross 
> distortion that increases with decreasing frequency

So my question is how can I demagnetise it or otherwise repair the tank? 
I know there was some discussion a while ago about repairing tanks, but 
not specifically demagnetising...
On the other hand, should I just buy a new tank? Where can I get one?

many thanks

James

PS - the transducer input impedance is 175 ohms and I temporarily 
connected another tank which worked fine.