Cossor501AC (Actually a 494AC) - raised from the grave? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Boater Sam · 13th Jul 2017, 10:58 pm

Capacitor across the output transformer primary?
And cap from the grid1 to ground?

Steve_P · 14th Jul 2017, 11:38 am

Have you tried another speaker? Always check the simple stuff first....

The Capacitor linking the Volume Control wiper to the grid of the First Audio amp.

There is a feedback loop on these - check it. And go in on the pick-up and see if that is clean.

Get the HT right first!

Cheers,

Steve P.

John G8MWF · 14th Jul 2017, 11:55 am

As previously mentioned the best HT I can get is approx. 230 volts.

My next step is to thoroughly clean the valve bases as all the usual suspects have been changed or checked.

telstar · 14th Jul 2017, 2:26 pm

Hi John.
I was unlucky with a Cossor 494A radio some time ago, the mains transformer secondary windings had been transposed and it had been burnt. It took some time to find a replacement, but eventually I got one.
Cheers
Mike

John G8MWF · 14th Jul 2017, 3:08 pm

Hello Mike, This one is still 'fighting' me!

Don't suppose you/anyone have a diagram for the 494? I have the 501 but there appear to be some big differences in the tone control wiring or modification by a previous engineer - there's only a cap from the Anode of V3 going into it and the wiper and other end of the pot are grounded - nothing like the 501 diagram!

The volume control is 1M not 500K etc. If it had Dilithium crystals I am sure that they would be blown as well!

Boater Sam · 14th Jul 2017, 5:54 pm

It will be on the service data top right of this page for the massive sum of £1.99 to support the forum. If the you can't get makers sheet, its Trader 924

Tone is as you say on 494, its a very simple top cut.

John G8MWF · 14th Jul 2017, 6:44 pm

Hello Sam,

Its finally alive!
There were a heck of a lot of wiring errors, bad components and dirty valve sockets. There's still a LOT to do and it's looking more like Frankenstein's monster than a radio with bits tagged on everywhere.

I am listening to Capital Gold at the moment with the odd crackle that may be due to the fault on the mains transformer but it does sound nice.

The HT is now being supplied by both the valve and semiconductors which I hope gives it a 'softer' start than having a solid stage bridge rectifier.

Thank you and everyone else for their help I really couldn't have done it without you.

Cheers

John

Boater Sam · 14th Jul 2017, 7:05 pm

Brilliant!
More of a rebirth than a repair. Its been fun to help, your determination is appreciated.
Sam

John G8MWF · 17th Jul 2017, 1:32 pm

The radio is now 'well' and all of the Arachnids have been cleaned out but I do have concern about the Christmas lights twin mains cable currently fitted to it.

It has a strain relief that consist of a knot in the cable inside the chassis and that's it.

Has anyone come up with a better solution that is sympathetic to safety and looks?

Kind regards

John

Boater Sam · 17th Jul 2017, 3:54 pm

A 3 core flex, maybe a bit of nice cotton covered like iron flex, 0.75 sq mm min, a grommet in the hole, "p" clip secured with a nut and bolt to restrain the cable. The Earth onto the chassis with a nut and bolt should be the longest wire, i.e. the last one to pull off in the event of the cable pulling out.
You should be able to drag the radio along a flat surface without pulling the cable out.
OR
File the hole to fit a 3 pin IEC C13 appliance socket and use a made up lead, as in computer lead.
Use a 1 Amp fuse, from electrical wholesaler.

TrevorG3VLF · 17th Jul 2017, 4:29 pm

I have used a wooden dowell and a clove hitch to restrain the cable. It does not bend the cable as tightly as a normal knot and can easily be repositioned.

John G8MWF · 19th Jul 2017, 4:31 pm

Hello Trevor et all,

I think that is the method I shall try first although I may use a plastic dowell of some description.

Many thanks - John

13th Jul 2017, 10:58 pm	#21
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Capacitor across the output transformer primary? And cap from the grid1 to ground?

14th Jul 2017, 11:38 am	#22
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Have you tried another speaker? Always check the simple stuff first.... The Capacitor linking the Volume Control wiper to the grid of the First Audio amp. There is a feedback loop on these - check it. And go in on the pick-up and see if that is clean. Get the HT right first! Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

14th Jul 2017, 11:55 am	#23
John G8MWF Hexode Join Date: Aug 2014 Location: Dartford, Kent, UK. Posts: 435	Re: Cossor501AC (Actually a 494AC) - raised from the grave? As previously mentioned the best HT I can get is approx. 230 volts. My next step is to thoroughly clean the valve bases as all the usual suspects have been changed or checked.

14th Jul 2017, 2:26 pm	#24
telstar Octode Join Date: Dec 2003 Location: Leeds, West Yorkshire, UK. Posts: 1,593	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Hi John. I was unlucky with a Cossor 494A radio some time ago, the mains transformer secondary windings had been transposed and it had been burnt. It took some time to find a replacement, but eventually I got one. Cheers Mike

14th Jul 2017, 3:08 pm	#25
John G8MWF Hexode Join Date: Aug 2014 Location: Dartford, Kent, UK. Posts: 435	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Hello Mike, This one is still 'fighting' me! Don't suppose you/anyone have a diagram for the 494? I have the 501 but there appear to be some big differences in the tone control wiring or modification by a previous engineer - there's only a cap from the Anode of V3 going into it and the wiper and other end of the pot are grounded - nothing like the 501 diagram! The volume control is 1M not 500K etc. If it had Dilithium crystals I am sure that they would be blown as well!

14th Jul 2017, 5:54 pm	#26
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor501AC (Actually a 494AC) - raised from the grave? It will be on the service data top right of this page for the massive sum of £1.99 to support the forum. If the you can't get makers sheet, its Trader 924 Tone is as you say on 494, its a very simple top cut. Last edited by Boater Sam; 14th Jul 2017 at 5:59 pm. Reason: added

14th Jul 2017, 6:44 pm	#27
John G8MWF Hexode Join Date: Aug 2014 Location: Dartford, Kent, UK. Posts: 435	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Hello Sam, Its finally alive! There were a heck of a lot of wiring errors, bad components and dirty valve sockets. There's still a LOT to do and it's looking more like Frankenstein's monster than a radio with bits tagged on everywhere. I am listening to Capital Gold at the moment with the odd crackle that may be due to the fault on the mains transformer but it does sound nice. The HT is now being supplied by both the valve and semiconductors which I hope gives it a 'softer' start than having a solid stage bridge rectifier. Thank you and everyone else for their help I really couldn't have done it without you. Cheers John

14th Jul 2017, 7:05 pm	#28
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Brilliant! More of a rebirth than a repair. Its been fun to help, your determination is appreciated. Sam

17th Jul 2017, 1:32 pm	#29
John G8MWF Hexode Join Date: Aug 2014 Location: Dartford, Kent, UK. Posts: 435	Re: Cossor501AC (Actually a 494AC) - raised from the grave? The radio is now 'well' and all of the Arachnids have been cleaned out but I do have concern about the Christmas lights twin mains cable currently fitted to it. It has a strain relief that consist of a knot in the cable inside the chassis and that's it. Has anyone come up with a better solution that is sympathetic to safety and looks? Kind regards John

17th Jul 2017, 3:54 pm	#30
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Cossor501AC (Actually a 494AC) - raised from the grave? A 3 core flex, maybe a bit of nice cotton covered like iron flex, 0.75 sq mm min, a grommet in the hole, "p" clip secured with a nut and bolt to restrain the cable. The Earth onto the chassis with a nut and bolt should be the longest wire, i.e. the last one to pull off in the event of the cable pulling out. You should be able to drag the radio along a flat surface without pulling the cable out. OR File the hole to fit a 3 pin IEC C13 appliance socket and use a made up lead, as in computer lead. Use a 1 Amp fuse, from electrical wholesaler. Last edited by Boater Sam; 17th Jul 2017 at 3:56 pm. Reason: addition

17th Jul 2017, 4:29 pm	#31
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Cossor501AC (Actually a 494AC) - raised from the grave? I have used a wooden dowell and a clove hitch to restrain the cable. It does not bend the cable as tightly as a normal knot and can easily be repositioned.

19th Jul 2017, 4:31 pm	#32
John G8MWF Hexode Join Date: Aug 2014 Location: Dartford, Kent, UK. Posts: 435	Re: Cossor501AC (Actually a 494AC) - raised from the grave? Hello Trevor et all, I think that is the method I shall try first although I may use a plastic dowell of some description. Many thanks - John