GEC BC4750 capacitor question - UK Vintage Radio Repair and Restoration Discussion Forum

Atlantic 52 · 18th Jun 2019, 9:45 pm

Hello,
At a recent car boot sale I couldn't resist a rather dirty but very unmolested GEC BC4750 dated January 1949. The set is amazing as I can't find any evidence of any component replacements. It had a very tatty 2 pin 5A plug on it and was thick with dust. Before I condemn the usual coupling / decoupling capacitors and before doing anything else, I wanted to ask how these 'EC' capacitors compare with the Hunts wax types. The ones in the set are hard plastic axial types marked EC and I have not come across these before. Are they just as likely to be leaky?
The build quality of this set is rather impressive and no doubt quite a nice radio in its day. Thankfully the wood slats are intact. I just need to re-finish the cabinet now its all been cleaned up.
Many thanks.

Nuvistor · 18th Jun 2019, 9:49 pm

No experience of EC capacitors but I would want to replace them, I expect them to be paper dielectric with all the problems those have.

slidertogrid · 18th Jun 2019, 11:04 pm

A lot depends on how the set has been stored if it's been in a damp environment moisture could have got into the capacitors. The best way would be to test them, if the capacitance is miles out that's usually a sign that they are leaky. It also depends on where in the circuit the capacitor is as to how much effect leakage has. I have a few sets which work well still on their original capacitors and others where every one has had to be changed.

I always try to reuse the original cases where possible or at least disguise the new capacitors in some way. To me an old chassis full of bright yellow capacitors just looks wrong.

It looks like a nice set in as you say original unspoilt condition!

Rich.

AC/HL · 18th Jun 2019, 11:59 pm

Do they all say EC, they could be GEC?

dazzlevision · 19th Jun 2019, 7:43 am

Quote:

Originally Posted by AC/HL

Do they all say EC, they could be GEC?

I’m pretty sure they are GEC’s own manufacture.

Heatercathodeshort · 19th Jun 2019, 7:50 am

Yes, GEC manufacture and probably all very leaky by now. They are 60 years beyond their design life. John.

Tim · 19th Jun 2019, 8:45 am

I did one of these a few years ago, and found the wax capacitors to be no different from any others. ie. electrically leaky. The one on the tone control was so bad it was putting enough current through the tone control to cause an audible arcing. The filter caps were bad too, but easy to fit new ones atop the chassis as there is plenty of space.

crackle · 19th Jun 2019, 8:59 am

Connect them up to the HT+ and negative chassis via a 22k resistor and measure the DC current passing through them. Start off on a 10mA range and switch down to a 50uA range.
If they are good there will be no measurable leakage current.

Mike

Atlantic 52 · 19th Jun 2019, 11:33 am

Many thanks to you all for your valued experiences. I'll check it all out carefully and expect the worst!

18th Jun 2019, 9:45 pm	#1
Atlantic 52 Pentode Join Date: Feb 2014 Location: Aldershot, Hampshire, UK. Posts: 108	GEC BC4750 capacitor question Hello, At a recent car boot sale I couldn't resist a rather dirty but very unmolested GEC BC4750 dated January 1949. The set is amazing as I can't find any evidence of any component replacements. It had a very tatty 2 pin 5A plug on it and was thick with dust. Before I condemn the usual coupling / decoupling capacitors and before doing anything else, I wanted to ask how these 'EC' capacitors compare with the Hunts wax types. The ones in the set are hard plastic axial types marked EC and I have not come across these before. Are they just as likely to be leaky? The build quality of this set is rather impressive and no doubt quite a nice radio in its day. Thankfully the wood slats are intact. I just need to re-finish the cabinet now its all been cleaned up. Many thanks. Attached Thumbnails

18th Jun 2019, 9:49 pm	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: GEC BC4750 capacitor question No experience of EC capacitors but I would want to replace them, I expect them to be paper dielectric with all the problems those have. __________________ Frank

18th Jun 2019, 11:04 pm	#3
slidertogrid Octode Join Date: Apr 2005 Location: Peterborough, Cambridgeshire, UK. Posts: 1,898	Re: GEC BC4750 capacitor question A lot depends on how the set has been stored if it's been in a damp environment moisture could have got into the capacitors. The best way would be to test them, if the capacitance is miles out that's usually a sign that they are leaky. It also depends on where in the circuit the capacitor is as to how much effect leakage has. I have a few sets which work well still on their original capacitors and others where every one has had to be changed. I always try to reuse the original cases where possible or at least disguise the new capacitors in some way. To me an old chassis full of bright yellow capacitors just looks wrong. It looks like a nice set in as you say original unspoilt condition! Rich.

18th Jun 2019, 11:59 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: GEC BC4750 capacitor question Do they all say EC, they could be GEC?

19th Jun 2019, 7:50 am	#6
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: GEC BC4750 capacitor question Yes, GEC manufacture and probably all very leaky by now. They are 60 years beyond their design life. John.

19th Jun 2019, 8:45 am	#7
Tim Dekatron Join Date: Jan 2003 Location: Bradford on Avon, Wiltshire, UK. Posts: 3,310	Re: GEC BC4750 capacitor question I did one of these a few years ago, and found the wax capacitors to be no different from any others. ie. electrically leaky. The one on the tone control was so bad it was putting enough current through the tone control to cause an audible arcing. The filter caps were bad too, but easy to fit new ones atop the chassis as there is plenty of space. __________________ "Nothing is as dangerous as being too modern;one is apt to grow old fashioned quite suddenly."

19th Jun 2019, 8:59 am	#8
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: GEC BC4750 capacitor question Connect them up to the HT+ and negative chassis via a 22k resistor and measure the DC current passing through them. Start off on a 10mA range and switch down to a 50uA range. If they are good there will be no measurable leakage current. Mike

19th Jun 2019, 11:33 am	#9
Atlantic 52 Pentode Join Date: Feb 2014 Location: Aldershot, Hampshire, UK. Posts: 108	Re: GEC BC4750 capacitor question Many thanks to you all for your valued experiences. I'll check it all out carefully and expect the worst!