How to adjust coil by coin? (3 replies)

I was check my IIB coil and this coil is almost out of specification. R&C knobs starting point is not in 12 o'clock. I was switch this coil to IIBa... and this coil doesn't calibrate. Doesn't work with IIBa. If you push coil calibartion button, you will get only one low, grunt sound, not few like with healthy coil..

So, I was hear about coin trick, to attach coin to broken coil (center) and than calibrate. I was check this method... and coil pass calibration process... and coil works good enough.

Any other tips? What coin? Silver, copper or doesn't matter?