Codar CR70A - UK Vintage Radio Repair and Restoration Discussion Forum

avometereight · 5th Mar 2007, 7:51 pm

Hi everyone
I have a Codar CR70A receiver which I purchased new in 1972.
It has been laid up in my mothers loft for the past 15 years, I recently found it and have been using it for the past few month with no problems.
I left it on standby at the weekend and forgot about it for 2 hours, when I came back into the room, there was a strong smell of burning and the backlight was dim.
Upon examination, the mains transformer T4 has burnt out.
Can anyone tell me if a modern alternative is available and where to get one?
Thanks.

Ian - G4JQT · 5th Mar 2007, 8:54 pm

Looks like a fairly standard 250-0-250 with 6.3v heater. I'd guess the HT winding is 50mA and LT 1A.

The manual says the auxiliary socket at the rear supplies other equipment HT 230V 20mA and LT 0.75A so that should be a guide.

But what caused the mains transformer to burn out? Has it actually been damaged? Usual suspects: Smoothing capacitors, HT wiring, V5. If the 2K resistor between the smoothing caps looks cooked, check second smoothing cap (furthest from V5 in electrical terms!) and then other HT faults.

I have a manual (Codar's usual poor attempt) if you want a copy. Though it's not a workshop manual, just user's.

IMO this is a surprisingly poor set! Codar did a very good tx (AT5) and the PR40 preselector was pretty good, but this receiver is nothing more than a domestic set witha BFO in metal box.

Although re-reading your post, shorted HT may not affect the LT (from which the backlight is presumably powered?) that much... Is it just the LT windings with a fault?

Ian

avometereight · 5th Mar 2007, 9:40 pm

Hi Ian
Thanks for your reply.
I guess that just the LT is faulty as the valves all light up OK.
The transformer has dumped a pile of cream wax onto the bottom of the case.
I have a manual and a circuit diagram, thanks for the offer.
I have had a good look around the circuit and cannot see any other signs of cooked components, although I am not an electronics expert.

avometereight · 25th Mar 2007, 5:07 pm

Hi
I posted a message a couple of weeks ago regarding replacing the faulty mains transformer on my Codar CR70A receiver.
I have had a good look around on the net today and found one on the Maplins website.
It is a N90CC valve power transformer. 230V HT and 6.3V LT.
Can anyone tell me if this one is suitable.
Regards

Station X · 25th Mar 2007, 5:19 pm

Here's a link to the Maplin Transformer:-

http://www.maplin.co.uk/Search.aspx?...source=15&SD=Y

It looks fine for the job if there's room for it and it can supply enough current.

Add up the heater curents of all the valves in the set to be sure the rating of the LT winding is not exceeded.

Do the same for the HT winding by adding up all the anode and screen currents.
Before you replace it check why it failed in the first place though. Read post 2 in this thread again.

The manual and circuit for this set can be downloaded here:-

http://www.portabletubes.co.uk/sitefiles/downloads.htm

avometereight · 9th Apr 2007, 4:59 pm

Hi everyone
I removed the original faulty mains transformer today and fitted the Maplin transformer, all is well, the set performs better than before.
If anyone else requires a replacement transformer for the CR70A, this is the one.
Thanks for your help.

5th Mar 2007, 7:51 pm	#1
avometereight Retired Dormant Member Join Date: Mar 2007 Location: Wiltshire Posts: 4	Codar CR70A Hi everyone I have a Codar CR70A receiver which I purchased new in 1972. It has been laid up in my mothers loft for the past 15 years, I recently found it and have been using it for the past few month with no problems. I left it on standby at the weekend and forgot about it for 2 hours, when I came back into the room, there was a strong smell of burning and the backlight was dim. Upon examination, the mains transformer T4 has burnt out. Can anyone tell me if a modern alternative is available and where to get one? Thanks.

5th Mar 2007, 8:54 pm	#2
Ian - G4JQT Octode Join Date: Jun 2004 Location: Reading/Fakenham, UK. Posts: 1,323	Re: Codar cR70A Looks like a fairly standard 250-0-250 with 6.3v heater. I'd guess the HT winding is 50mA and LT 1A. The manual says the auxiliary socket at the rear supplies other equipment HT 230V 20mA and LT 0.75A so that should be a guide. But what caused the mains transformer to burn out? Has it actually been damaged? Usual suspects: Smoothing capacitors, HT wiring, V5. If the 2K resistor between the smoothing caps looks cooked, check second smoothing cap (furthest from V5 in electrical terms!) and then other HT faults. I have a manual (Codar's usual poor attempt) if you want a copy. Though it's not a workshop manual, just user's. IMO this is a surprisingly poor set! Codar did a very good tx (AT5) and the PR40 preselector was pretty good, but this receiver is nothing more than a domestic set witha BFO in metal box. Although re-reading your post, shorted HT may not affect the LT (from which the backlight is presumably powered?) that much... Is it just the LT windings with a fault? Ian

5th Mar 2007, 9:40 pm	#3
avometereight Retired Dormant Member Join Date: Mar 2007 Location: Wiltshire Posts: 4	Re: Codar cR70A Hi Ian Thanks for your reply. I guess that just the LT is faulty as the valves all light up OK. The transformer has dumped a pile of cream wax onto the bottom of the case. I have a manual and a circuit diagram, thanks for the offer. I have had a good look around the circuit and cannot see any other signs of cooked components, although I am not an electronics expert.

25th Mar 2007, 5:07 pm	#4
avometereight Retired Dormant Member Join Date: Mar 2007 Location: Wiltshire Posts: 4	Codar cR70A mains transformer Hi I posted a message a couple of weeks ago regarding replacing the faulty mains transformer on my Codar CR70A receiver. I have had a good look around on the net today and found one on the Maplins website. It is a N90CC valve power transformer. 230V HT and 6.3V LT. Can anyone tell me if this one is suitable. Regards

25th Mar 2007, 5:19 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Codar CR70A Here's a link to the Maplin Transformer:- http://www.maplin.co.uk/Search.aspx?...source=15&SD=Y It looks fine for the job if there's room for it and it can supply enough current. Add up the heater curents of all the valves in the set to be sure the rating of the LT winding is not exceeded. Do the same for the HT winding by adding up all the anode and screen currents. Before you replace it check why it failed in the first place though. Read post 2 in this thread again. The manual and circuit for this set can be downloaded here:- http://www.portabletubes.co.uk/sitefiles/downloads.htm __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

9th Apr 2007, 4:59 pm	#6
avometereight Retired Dormant Member Join Date: Mar 2007 Location: Wiltshire Posts: 4	Re: Codar CR70A Hi everyone I removed the original faulty mains transformer today and fitted the Maplin transformer, all is well, the set performs better than before. If anyone else requires a replacement transformer for the CR70A, this is the one. Thanks for your help.