Ducretet Thomson C635 1935 - UK Vintage Radio Repair and Restoration Discussion Forum

Wishiknewmore · 29th Jun 2020, 3:29 pm

Hello,

Just got this set – it looks like it has been in a barn since the war but it is complete

To establish if there are enough functioning bits on it I have:
Set the voltage to 225-250v
Replaced grid capacitor C1
Replaced two big 8uf electrolytics C5 & C6 with 10uf as C6 started to get warm
Replaced C29 as it started to grow in front of me!

Voltages on rectifier:
4.7v on heaters
338vac on both plates
322vdc – cathodes

Voltage output:
Pin 1 & 6 heater 6vac
2 Anode 199v
3 Grid 2 219v
4 Grid 1 -16v
5 Cathode 0v

However not a squeak from the speaker. I think I have diagnosed that as an open voice coil

I have connected a modern 8 ohm speaker across the contacts on the output transformer that connected to the voice coil and I have some low output and one very weak station!

QUESTIONS:

Are the valve voltages reasonable?
Is it possible/realistic to rewind a voice coil?
Dial cord is broken but it is stranded steel wire approx. 0.3mm in diameter – any suggestions for replacement?

https://www.doctsf.com/ducretet-thom...5/f3749/ori=ps

As always thoughts and suggestions welcome

many thanks

Philip

Wishiknewmore · 3rd Jul 2020, 10:59 am

Having spent some time looking at voice coil rewinds the inter-web is may well be above my pay grade!
The field coil is working as is creates a magnet, which I understand is also a choke/ inductor in the power supply.
So could I replace the 10inch speaker with a more modern unit, if so what impedance and what do I do about the choke function?
Thanks
Philip

vinrads · 3rd Jul 2020, 11:29 am

Hi Philip have you checked to see if the pig tails are ok sometimes the can look ok but be o/c these are the flexible wires connecting the coil to the L/S terminals . If the voice coil is o/c ,fit a new speaker , remove the field coil mount it separate to the spk. That could be a very nice looking radio. Good luck Mick.

Wishiknewmore · 3rd Jul 2020, 11:52 am

Thanks Mick
I will check out the pig tails
I think it has the potential to be a good looker although it may be a long project, at the moment I'm just at the evaluation and conservation point, as I found a few woodworm holes I treated the case and glued down some loose veneer, bit of switch cleaner and radio 4 long wave appeared ...so there is hope!
Philip

29th Jun 2020, 3:29 pm	#1
Wishiknewmore Hexode Join Date: Oct 2016 Location: Darlington, County Durham, UK. Posts: 343	Ducretet Thomson C635 1935 Hello, Just got this set – it looks like it has been in a barn since the war but it is complete To establish if there are enough functioning bits on it I have: Set the voltage to 225-250v Replaced grid capacitor C1 Replaced two big 8uf electrolytics C5 & C6 with 10uf as C6 started to get warm Replaced C29 as it started to grow in front of me! Voltages on rectifier: 4.7v on heaters 338vac on both plates 322vdc – cathodes Voltage output: Pin 1 & 6 heater 6vac 2 Anode 199v 3 Grid 2 219v 4 Grid 1 -16v 5 Cathode 0v However not a squeak from the speaker. I think I have diagnosed that as an open voice coil I have connected a modern 8 ohm speaker across the contacts on the output transformer that connected to the voice coil and I have some low output and one very weak station! QUESTIONS: Are the valve voltages reasonable? Is it possible/realistic to rewind a voice coil? Dial cord is broken but it is stranded steel wire approx. 0.3mm in diameter – any suggestions for replacement? https://www.doctsf.com/ducretet-thom...5/f3749/ori=ps As always thoughts and suggestions welcome many thanks Philip Attached Thumbnails

3rd Jul 2020, 10:59 am	#2
Wishiknewmore Hexode Join Date: Oct 2016 Location: Darlington, County Durham, UK. Posts: 343	Re: Ducretet Thomson C635 1935 Having spent some time looking at voice coil rewinds the inter-web is may well be above my pay grade! The field coil is working as is creates a magnet, which I understand is also a choke/ inductor in the power supply. So could I replace the 10inch speaker with a more modern unit, if so what impedance and what do I do about the choke function? Thanks Philip

3rd Jul 2020, 11:29 am	#3
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,766	Re: Ducretet Thomson C635 1935 Hi Philip have you checked to see if the pig tails are ok sometimes the can look ok but be o/c these are the flexible wires connecting the coil to the L/S terminals . If the voice coil is o/c ,fit a new speaker , remove the field coil mount it separate to the spk. That could be a very nice looking radio. Good luck Mick.

3rd Jul 2020, 11:52 am	#4
Wishiknewmore Hexode Join Date: Oct 2016 Location: Darlington, County Durham, UK. Posts: 343	Re: Ducretet Thomson C635 1935 Thanks Mick I will check out the pig tails I think it has the potential to be a good looker although it may be a long project, at the moment I'm just at the evaluation and conservation point, as I found a few woodworm holes I treated the case and glued down some loose veneer, bit of switch cleaner and radio 4 long wave appeared ...so there is hope! Philip