Cossor melody maker 501AC - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

cathoderay57 · 23rd Oct 2018, 10:23 pm

As mentioned here is a pic of the spare valves that I hold for this set; from left to right ECH35 (OM10), EF39 (OM6), EBC33 (OM4), Brimar 6V6GT, Cossor 6V6G, EZ35 (6X5G). You have a PM.

Guineafowl · 24th Oct 2018, 11:09 am

I stripped the IF tranny last night - coils reading 10 ohms and caps 100 nF as they should. No leakage evident in the caps either. I’ll try aligning again once the valves come from cathoderay57.

Also checked all the little square caps with one leg lifted - no leakage (Gohm range readings) at 100 vdc.

Boater Sam · 24th Oct 2018, 1:14 pm

The Cossor 500 series chassis is let down by the bottom coupled aerial coil.
I have several and most work to a good standard, not outstandingly sensitive.
One however is terrible and its the aerial coil that is at fault.
Why I cannot establish, it looks and measures resistance wise the same as others, obviously something is amiss with its Q.
I would attempt to rewind it but it is difficult to establish the internal connections as the winding ends disappear into the hollow center and the fine wire is buried in the wax.
If the set was more desirable I would try to redesign the front end with new coupled aerial coils.

ms660 · 24th Oct 2018, 4:17 pm

Some stuff about bottom end coupling in this article:

http://www.vintageradio.me.uk/radcon...mage/jan55.pdf

Lawrence..

kalee20 · 24th Oct 2018, 4:58 pm

Quote:

Originally Posted by Sideband

The Cossor 501 is not particularly sensitive... The DAC90A will far out-perform it

Quote:

Originally Posted by Boater Sam

The Cossor 500 series chassis is let down by the bottom coupled aerial coil.

Absolutely. It only has single-point tracking adjustment too, so the aerial coil is really only in tune at one point on the dial.

It also has simple AVC, about as basic as you can get, even though it does have a double-diode triode. The DAC90a has delayed AVC, giving better sensitivity with weak stations.

Its saving graces are that it has a good-size loudspeaker, and a good robust output valve (6V6 or equivalent). It has a mains transformer so runs cool. And it's dead easy to service, with everything well-spaced and accessible.

Looking forward to news on the IFT!

Guineafowl · 24th Oct 2018, 6:44 pm

Kalee20 - see above. I stripped the IFT and found no faults. Not sure why the top screw wouldn’t tune, but I report back once the new rectifier arrives.

Guineafowl · 30th Oct 2018, 6:07 pm

Right - valves arrived yesterday from Cathoderay57.

Swapped the knackered rectifier 6X5G for the NOS Elpico EZ35, and all the voltages jumped up to what they should be...

Except for V3 (OM-4, detector/preamp) whose anode voltage was too high. Swapped in the replacement and volume and general performance improved dramatically.

Fitted a 3-core, twisted flex with a nice bronze cloth outer. Aligned and reassembled.

It’s now sitting in the bedroom - reception is reasonable, although with some static in the background. Not sure if this is normal for these old things or not.

On SW there’s still some motorboating, but I never use that anyway.

Thanks all, especially Cathoderay57!

23rd Oct 2018, 10:23 pm	#21
cathoderay57 Nonode Join Date: Oct 2017 Location: Bristol, UK. Posts: 2,384	Re: Cossor melody maker 501AC As mentioned here is a pic of the spare valves that I hold for this set; from left to right ECH35 (OM10), EF39 (OM6), EBC33 (OM4), Brimar 6V6GT, Cossor 6V6G, EZ35 (6X5G). You have a PM. Attached Thumbnails

24th Oct 2018, 11:09 am	#22
Guineafowl Tetrode Join Date: Sep 2018 Location: Inverness, Scottish Highlands, UK. Posts: 74	Re: Cossor melody maker 501AC I stripped the IF tranny last night - coils reading 10 ohms and caps 100 nF as they should. No leakage evident in the caps either. I’ll try aligning again once the valves come from cathoderay57. Also checked all the little square caps with one leg lifted - no leakage (Gohm range readings) at 100 vdc.

24th Oct 2018, 1:14 pm	#23
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor melody maker 501AC The Cossor 500 series chassis is let down by the bottom coupled aerial coil. I have several and most work to a good standard, not outstandingly sensitive. One however is terrible and its the aerial coil that is at fault. Why I cannot establish, it looks and measures resistance wise the same as others, obviously something is amiss with its Q. I would attempt to rewind it but it is difficult to establish the internal connections as the winding ends disappear into the hollow center and the fine wire is buried in the wax. If the set was more desirable I would try to redesign the front end with new coupled aerial coils.

24th Oct 2018, 4:17 pm	#24
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Cossor melody maker 501AC Some stuff about bottom end coupling in this article: http://www.vintageradio.me.uk/radcon...mage/jan55.pdf Lawrence..

24th Oct 2018, 6:44 pm	#26
Guineafowl Tetrode Join Date: Sep 2018 Location: Inverness, Scottish Highlands, UK. Posts: 74	Re: Cossor melody maker 501AC Kalee20 - see above. I stripped the IFT and found no faults. Not sure why the top screw wouldn’t tune, but I report back once the new rectifier arrives.

30th Oct 2018, 6:07 pm	#27
Guineafowl Tetrode Join Date: Sep 2018 Location: Inverness, Scottish Highlands, UK. Posts: 74	Re: Cossor melody maker 501AC Right - valves arrived yesterday from Cathoderay57. Swapped the knackered rectifier 6X5G for the NOS Elpico EZ35, and all the voltages jumped up to what they should be... Except for V3 (OM-4, detector/preamp) whose anode voltage was too high. Swapped in the replacement and volume and general performance improved dramatically. Fitted a 3-core, twisted flex with a nice bronze cloth outer. Aligned and reassembled. It’s now sitting in the bedroom - reception is reasonable, although with some static in the background. Not sure if this is normal for these old things or not. On SW there’s still some motorboating, but I never use that anyway. Thanks all, especially Cathoderay57!