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quantum · 19th Apr 2003, 7:33 pm

This is a fault that I have come across on a couple of occasions with Cossor 500AC 'Melody Maker' sets, although the same problem could occur with any of the Cossor series with identical RF stages with their associated coils, namely the 494AC/U, 501AC/U and the 520AC.

With these sets the primary of the short wave oscillator coil is permanently in circuit, regardless of which waveband the set is tuned to. The primary of the MW/LW osc coil is connected in series with the SW osc coil primary, being shorted out when the the set is switched to SW. Thus if the osc coil primary is open circuit the set would not function on any waveband.

I have found sets with o/c osc coil primaries on two occasions - bypassing this primary restores the sets to operation on MW and LW, although not SW of course.

Why the osc coil primary should go o/c is not certain - it does not carry DC so perhaps it is just age or a quality problem in the original coil - after all, the sets were not designed with the thought of how they would operate in 50 years time!

19th Apr 2003, 7:33 pm	#1
quantum Retired Dormant Member Join Date: Mar 2003 Location: Birmingham, West Midlands, UK. Posts: 785	Cossor 500AC SW oscillator coil failure This is a fault that I have come across on a couple of occasions with Cossor 500AC 'Melody Maker' sets, although the same problem could occur with any of the Cossor series with identical RF stages with their associated coils, namely the 494AC/U, 501AC/U and the 520AC. With these sets the primary of the short wave oscillator coil is permanently in circuit, regardless of which waveband the set is tuned to. The primary of the MW/LW osc coil is connected in series with the SW osc coil primary, being shorted out when the the set is switched to SW. Thus if the osc coil primary is open circuit the set would not function on any waveband. I have found sets with o/c osc coil primaries on two occasions - bypassing this primary restores the sets to operation on MW and LW, although not SW of course. Why the osc coil primary should go o/c is not certain - it does not carry DC so perhaps it is just age or a quality problem in the original coil - after all, the sets were not designed with the thought of how they would operate in 50 years time!