08-11-2017, 09:24 PM
Picked this one off the pile, the last time the Cossor 520 was switched on was at least fifteen years ago.
The set did work in a fashion but it was evident the alignment was way out, stations were not tuning in on the correct positions on the tuning scale.
First confirm the IF is the correct 470Kc/s, it is. Adjustment the high frequency end of the medium waveband was easy enough but it was found that BBC Radio 4 which is 603Kc/s (approx. 500metres) was coming in on about 450M. There is no adjustable oscillator padder trimmer in this receiver, only mica capacitor C13 (450pF) The oscillator coil is an air core type, no adjustment there. The solution was found by experiment and in due course by inserting a 3000pF in series with C13 this action corrected the MW alignment problem. Check that the HF end of the MW is aligned correctly by injecting a 1550Kc/s signal and by adjusting C2 the scale point should line up with scale marker "M".
Long waves: only one adjustment, the padder trimmer C18. Inject 160Kc/s and confirm that the signal comes in when the scale pointer is coincident with marker "L". See attachment. In practise BBC R4 on 198Kc/s doesn't tune in on 1500M and C18 can be tweeked so that it does.
The Short waveband has three adjustments, the oscillator trimmer for 18Mc/s on scale marker left side "S" and adjustable oscillator core L7/8 for 6mc/s on scale marker right side "S".
Aerial trimmer peaks up on 18Mc/s.
All these adjustment have proven worthwhile, the receiver gives a good account of itself on all wavebands. RTE coming loud and clear on 282Kc/s. Short waves lively using a 10 feet of wire.
Geordie McBoyne.
The set did work in a fashion but it was evident the alignment was way out, stations were not tuning in on the correct positions on the tuning scale.
First confirm the IF is the correct 470Kc/s, it is. Adjustment the high frequency end of the medium waveband was easy enough but it was found that BBC Radio 4 which is 603Kc/s (approx. 500metres) was coming in on about 450M. There is no adjustable oscillator padder trimmer in this receiver, only mica capacitor C13 (450pF) The oscillator coil is an air core type, no adjustment there. The solution was found by experiment and in due course by inserting a 3000pF in series with C13 this action corrected the MW alignment problem. Check that the HF end of the MW is aligned correctly by injecting a 1550Kc/s signal and by adjusting C2 the scale point should line up with scale marker "M".
Long waves: only one adjustment, the padder trimmer C18. Inject 160Kc/s and confirm that the signal comes in when the scale pointer is coincident with marker "L". See attachment. In practise BBC R4 on 198Kc/s doesn't tune in on 1500M and C18 can be tweeked so that it does.
The Short waveband has three adjustments, the oscillator trimmer for 18Mc/s on scale marker left side "S" and adjustable oscillator core L7/8 for 6mc/s on scale marker right side "S".
Aerial trimmer peaks up on 18Mc/s.
All these adjustment have proven worthwhile, the receiver gives a good account of itself on all wavebands. RTE coming loud and clear on 282Kc/s. Short waves lively using a 10 feet of wire.
Geordie McBoyne.
