My Second Radialva Groom Restore

[Yorkie]

the field coil of a speaker is use instead of a choke in the power suppy.connected between the smoothing and reservoir cap buget circuits use a resistor.the effect of the currant though the field coil turns the centre pole into a powerfull magnet.
rob t

Yes, I understand that Rob, but surely in terms of voltage drop, as the 3,000R field coil (acting in its dual role as a smoothing choke) carries the HT to the radio, such a high resistance will drop too much voltage when fed from 110V mains, as would a 3K resistor in the same position between smoother/reservoir caps. But now that John has the circuit, it's apparent that the field coil doesn't in fact carry the full HT. The DC comes off the cathodes of the rectifier and there is 105V at that point, which the field coil has no influence over as all of the HT doesn't pass through it. I suppose the issue then becomes whether or not the 450 Ohm field coil will draw excess current as compared to the specified 3,000. Maybe the only was of knowing would be to check the voltage drop across the coil to find out from Ohms law what current is flowing in the field coil. The usual reason for field coils failing is due to excess current being drawn when DC blocking caps become leaky, given that the coils consist of many thousands of fine wire - 48SWG I'd guess.