Cossor 497A.C - UK Vintage Radio Repair and Restoration Discussion Forum

vampyretim · 25th Jul 2019, 2:14 pm

Hello,

I'm trying to repair the above radio and the top cap of the OM-10 isn't connected to anything it just has a loose wire hanging from it. I can't work out from the schematic or from the valve data where this should be connected.

Would someone mind looking over the schematic and point out where I'm going wrong please?

Cobaltblue · 25th Jul 2019, 2:30 pm

Hi Tim is this a 487 rather than a 497 which ISTR is a Radiogram ?

If it the 487 then the top cap should go to the Capacitor an resistor on the back of the tuning gang.

Cheers

Mike T

Nanozeugma · 25th Jul 2019, 3:01 pm

As said, you likely mean the 487 as the 497 is a radiogram which uses B8B valves.
The 487 uses an OM-10 frequency changer (V1.)
The top cap is the control grid of the Hexode section.
It connects to the junction of C9 and R3 which are located on the back of the tuning capacitor.

Cobaltblue · 25th Jul 2019, 3:18 pm

Haha at least someone is using my website

Cheers

Mike T

Nanozeugma · 25th Jul 2019, 3:38 pm

Indeed, a most valuable resource, my complements

vampyretim · 26th Jul 2019, 12:40 pm

Thanks guys,

Yes it was a 487!

My mistake.

vampyretim · 26th Jul 2019, 1:04 pm

I'm a bit low on H.T. It has at one time had a replacement output transformer installed but I'm getting 342v A.C on the anodes and only 220v at the cathode of the rectifier.

Could the 6X5G be low on emissions? Could I just replace with diodes if so?

Nanozeugma · 26th Jul 2019, 11:06 pm

When you say "output transformer," just to clarify, the audio output transformer?
Before you condemn the rectifier http://www.r-type.org/exhib/aad0070.htm ...
have you eliminated a knackered reservoir capacitor?
Replacing a valve rectifier with modern silicon diodes would be the last resort for me - as in a replacement was made of unobtainium.
The GT equivalent seems available if you need one... here's one... https://www.ebay.co.uk/itm/BRIMAR-6X...UAAOSwsnldGQEO

25th Jul 2019, 2:14 pm	#1
vampyretim Heptode Join Date: Aug 2011 Location: Bristol, UK. Posts: 538	Cossor 497A.C Hello, I'm trying to repair the above radio and the top cap of the OM-10 isn't connected to anything it just has a loose wire hanging from it. I can't work out from the schematic or from the valve data where this should be connected. Would someone mind looking over the schematic and point out where I'm going wrong please?

25th Jul 2019, 2:30 pm	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: Cossor 497A.C Hi Tim is this a 487 rather than a 497 which ISTR is a Radiogram ? If it the 487 then the top cap should go to the Capacitor an resistor on the back of the tuning gang. Cheers Mike T Attached Thumbnails __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk Last edited by Cobaltblue; 25th Jul 2019 at 2:37 pm.

25th Jul 2019, 3:01 pm	#3
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: Cossor 497A.C As said, you likely mean the 487 as the 497 is a radiogram which uses B8B valves. The 487 uses an OM-10 frequency changer (V1.) The top cap is the control grid of the Hexode section. It connects to the junction of C9 and R3 which are located on the back of the tuning capacitor. Attached Thumbnails __________________ Thermionic Emission, warms the cockles of your tubes.

25th Jul 2019, 3:18 pm	#4
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,864	Re: Cossor 497A.C Haha at least someone is using my website Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

25th Jul 2019, 3:38 pm	#5
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: Cossor 497A.C Indeed, a most valuable resource, my complements __________________ Thermionic Emission, warms the cockles of your tubes.

26th Jul 2019, 12:40 pm	#6
vampyretim Heptode Join Date: Aug 2011 Location: Bristol, UK. Posts: 538	Re: Cossor 497A.C Thanks guys, Yes it was a 487! My mistake.

26th Jul 2019, 1:04 pm	#7
vampyretim Heptode Join Date: Aug 2011 Location: Bristol, UK. Posts: 538	Re: Cossor 497A.C I'm a bit low on H.T. It has at one time had a replacement output transformer installed but I'm getting 342v A.C on the anodes and only 220v at the cathode of the rectifier. Could the 6X5G be low on emissions? Could I just replace with diodes if so?

26th Jul 2019, 11:06 pm	#8
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: Cossor 497A.C When you say "output transformer," just to clarify, the audio output transformer? Before you condemn the rectifier http://www.r-type.org/exhib/aad0070.htm ... have you eliminated a knackered reservoir capacitor? Replacing a valve rectifier with modern silicon diodes would be the last resort for me - as in a replacement was made of unobtainium. The GT equivalent seems available if you need one... here's one... https://www.ebay.co.uk/itm/BRIMAR-6X...UAAOSwsnldGQEO __________________ Thermionic Emission, warms the cockles of your tubes.