GEC BC 3780 radio - UK Vintage Radio Repair and Restoration Discussion Forum

martin.m · 7th Aug 2018, 7:34 pm

I acquired this one a few days ago. Am I correct in thinking this model is pre-war, as there is no Home, Light or Third on the tuning dial? I won't have time to have a proper look for a while but it appears to have a Push Pull audio output stage. There doesn't seem to be any service information for a BC 3780 on this site. Has anyone restored one of these?

Cobaltblue · 7th Aug 2018, 7:46 pm

Yes your right Pre War 1937/8

I might have the orignal GEC service Data struggling with so much in storage at the moment to think where it is though

Cheers

Mike T

McMurdo · 7th Aug 2018, 7:48 pm

Push pull MPT4 pair. Service sheet is dated 1936. It's an 8-valve set. (maybe?)

Ed_Dinning · 7th Aug 2018, 7:54 pm

Hi Martin, give me a call if you get stuck when you start on it as I might have some of the data, but should be able to assist with valve checks etc.

Ed

martin.m · 7th Aug 2018, 11:24 pm

Thank you Ed. It might be a while before I get a proper look. I've never had a pre-war set to fix before. This one seems to be built like a battleship and I've no idea what all the sockets on the back are for. So many projects, so little time (and a wife who doesn't drive).

Regards
Martin

ColinB · 8th Aug 2018, 6:41 am

Definitely pre war, as others have said. A dead give away is the National and Regional markings on the dial.

Nice set, good luck with the restoration.

martin.m · 8th Aug 2018, 8:32 am

Thanks Colin, before I even start I will need a suitable mains connector. It's a 5 amp round pin type, the same as used on the Bush DAC90. I have posted on the "parts wanted" section of this site. If anybody has one for sale, please message me. A flat one will do just as well as the 90 degree type.

Regards
Martin

Ed_Dinning · 8th Aug 2018, 8:42 am

Hi Martin, I'll see if I can find a suitable socket.
Outlets on the back could be any or all of the following:
Extension speaker, pick up (gram) input, mains for gram motor, Aerial and Earth.

Ed

martin.m · 8th Aug 2018, 8:45 am

I was curious about some of the station names on the tuning dial so looked them up on the Internet. I didn't know that Athlone is in Ireland and Lahti in Finland. The transmitter at Sottens in Switzerland was taken out of service in 2010 and the mast demolished a few years later. So sad.

martin.m · 8th Aug 2018, 8:55 am

Thank you Ed. I have located an original GEC service manual for sale on the Internet. It's a bit pricey at £17 but will save lots of time when repairing a set like this.

Regards
Martin

PJL · 8th Aug 2018, 10:29 am

Check the transformer continuity before you get stuck in. The output transformers in these pre-war PP sets are prone to failure.

Mr Moose · 8th Aug 2018, 5:16 pm

Hello,
I think this is the correct service data for your set https://www.service-data.com/product...95/3337/b12295 as it is the Broadcaster sheet for the "Fidelity All Wave" reciever and is from April 1936.
Paul's description says it is for the BC3880 which is the "Fidelity All Wave 8" but this came out in 1937 not 1936 and has a vertical bar across the speaker grill not shown on the picture on the Broadcaster sheet.
I suspect that the two chassis of the 3780 and 3880 are almost the same if not the same.
Yours, Richard

martin.m · 8th Aug 2018, 8:02 pm

Thank you Richard. It looks like the two models use the same chassis. There is a picture of an advert for the 3880 on the Radiomuseum website. The valve line up is the same apart from the rectifier (MU14 in the 3780 rather than a U14). I will go ahead and order the service data.

Regards
Martin

Mr Moose · 8th Aug 2018, 9:03 pm

Hello,
Looking at the circuits for the Broadcaster sheet for the "Fidelity All Wave" reciever and the GEC service data for the "Fidelity All Wave 8" (both on Paul's CD), the chassis layout and valves are the same and the circuit is almost the same but there are a number of resistors and capacitors which have different values between the two sets but these are almost all in the HF stages.
Yours, Richard

martin.m · 8th Aug 2018, 10:00 pm

This set is quite elaborate with 8 valves. RF amp, Mixer/oscillator, 2 IF stages, audio amp, Push-Pull output stage and FW rectifier. I don't think getting it working again will be as straightforward as fixing a run of the mill post-war superhet.

turretslug · 8th Aug 2018, 11:29 pm

I dare say it will be a challenge, but one with a rewarding and worthwhile result. As you say, plenty more in the circuitry than a mundane post-war 4 + R, plus deteriorated wiring and valves that could have flaking screening and un-stuck bases (though their basic function could well be pretty good still). I haven't looked at the circuit, but an energised speaker and quite involved biasing arrangements are also likely to feature.

Nonetheless, far more characterful and worthy than that mundane post-war set, and something with that specification and "all-wave" (like that phrase) coverage would have been an expensive source of pride and interest back then- think the large-screen telly, high-spec computer and fast internet connection of its time and then some! It'll still perform well today after overhaul. I love the idea of someone back then tuning around for the stations on radio scales- a pre-war set here made me check the likes of Banska Bystrica, Finnmark, Sverdlovsk etc. on the map.

Good luck with it, there'll be plenty of advice and encouragement on the forum.

7th Aug 2018, 7:34 pm	#1
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	GEC BC 3780 radio I acquired this one a few days ago. Am I correct in thinking this model is pre-war, as there is no Home, Light or Third on the tuning dial? I won't have time to have a proper look for a while but it appears to have a Push Pull audio output stage. There doesn't seem to be any service information for a BC 3780 on this site. Has anyone restored one of these? Attached Thumbnails __________________ Regards Martin

7th Aug 2018, 7:46 pm	#2
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,863	Re: GEC BC 3780 radio Yes your right Pre War 1937/8 I might have the orignal GEC service Data struggling with so much in storage at the moment to think where it is though Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

7th Aug 2018, 7:48 pm	#3
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,270	Re: GEC BC 3780 radio Push pull MPT4 pair. Service sheet is dated 1936. It's an 8-valve set. (maybe?) __________________ Kevin

7th Aug 2018, 7:54 pm	#4
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: GEC BC 3780 radio Hi Martin, give me a call if you get stuck when you start on it as I might have some of the data, but should be able to assist with valve checks etc. Ed

7th Aug 2018, 11:24 pm	#5
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio Thank you Ed. It might be a while before I get a proper look. I've never had a pre-war set to fix before. This one seems to be built like a battleship and I've no idea what all the sockets on the back are for. So many projects, so little time (and a wife who doesn't drive). Regards Martin

8th Aug 2018, 6:41 am	#6
ColinB Heptode Join Date: Apr 2003 Location: Newton Abbot, Devon, UK. Posts: 761	Re: GEC BC 3780 radio Definitely pre war, as others have said. A dead give away is the National and Regional markings on the dial. Nice set, good luck with the restoration.

8th Aug 2018, 8:32 am	#7
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio Thanks Colin, before I even start I will need a suitable mains connector. It's a 5 amp round pin type, the same as used on the Bush DAC90. I have posted on the "parts wanted" section of this site. If anybody has one for sale, please message me. A flat one will do just as well as the 90 degree type. Regards Martin __________________ Regards Martin

8th Aug 2018, 8:42 am	#8
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: GEC BC 3780 radio Hi Martin, I'll see if I can find a suitable socket. Outlets on the back could be any or all of the following: Extension speaker, pick up (gram) input, mains for gram motor, Aerial and Earth. Ed

8th Aug 2018, 8:45 am	#9
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio I was curious about some of the station names on the tuning dial so looked them up on the Internet. I didn't know that Athlone is in Ireland and Lahti in Finland. The transmitter at Sottens in Switzerland was taken out of service in 2010 and the mast demolished a few years later. So sad.

8th Aug 2018, 8:55 am	#10
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio Thank you Ed. I have located an original GEC service manual for sale on the Internet. It's a bit pricey at £17 but will save lots of time when repairing a set like this. Regards Martin

8th Aug 2018, 10:29 am	#11
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: GEC BC 3780 radio Check the transformer continuity before you get stuck in. The output transformers in these pre-war PP sets are prone to failure.

8th Aug 2018, 5:16 pm	#12
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: GEC BC 3780 radio Hello, I think this is the correct service data for your set https://www.service-data.com/product...95/3337/b12295 as it is the Broadcaster sheet for the "Fidelity All Wave" reciever and is from April 1936. Paul's description says it is for the BC3880 which is the "Fidelity All Wave 8" but this came out in 1937 not 1936 and has a vertical bar across the speaker grill not shown on the picture on the Broadcaster sheet. I suspect that the two chassis of the 3780 and 3880 are almost the same if not the same. Yours, Richard

8th Aug 2018, 8:02 pm	#13
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio Thank you Richard. It looks like the two models use the same chassis. There is a picture of an advert for the 3880 on the Radiomuseum website. The valve line up is the same apart from the rectifier (MU14 in the 3780 rather than a U14). I will go ahead and order the service data. Regards Martin

8th Aug 2018, 9:03 pm	#14
Mr Moose Octode Join Date: Jul 2008 Location: Gloucestershire, UK. Posts: 1,043	Re: GEC BC 3780 radio Hello, Looking at the circuits for the Broadcaster sheet for the "Fidelity All Wave" reciever and the GEC service data for the "Fidelity All Wave 8" (both on Paul's CD), the chassis layout and valves are the same and the circuit is almost the same but there are a number of resistors and capacitors which have different values between the two sets but these are almost all in the HF stages. Yours, Richard

8th Aug 2018, 10:00 pm	#15
martin.m Hexode Join Date: Mar 2018 Location: Bishop Auckland, County Durham, UK. Posts: 373	Re: GEC BC 3780 radio This set is quite elaborate with 8 valves. RF amp, Mixer/oscillator, 2 IF stages, audio amp, Push-Pull output stage and FW rectifier. I don't think getting it working again will be as straightforward as fixing a run of the mill post-war superhet. __________________ Regards Martin Last edited by martin.m; 8th Aug 2018 at 10:01 pm. Reason: Typo

8th Aug 2018, 11:29 pm	#16
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,394	Re: GEC BC 3780 radio I dare say it will be a challenge, but one with a rewarding and worthwhile result. As you say, plenty more in the circuitry than a mundane post-war 4 + R, plus deteriorated wiring and valves that could have flaking screening and un-stuck bases (though their basic function could well be pretty good still). I haven't looked at the circuit, but an energised speaker and quite involved biasing arrangements are also likely to feature. Nonetheless, far more characterful and worthy than that mundane post-war set, and something with that specification and "all-wave" (like that phrase) coverage would have been an expensive source of pride and interest back then- think the large-screen telly, high-spec computer and fast internet connection of its time and then some! It'll still perform well today after overhaul. I love the idea of someone back then tuning around for the stations on radio scales- a pre-war set here made me check the likes of Banska Bystrica, Finnmark, Sverdlovsk etc. on the map. Good luck with it, there'll be plenty of advice and encouragement on the forum.