Double Decca MB5 - UK Vintage Radio Repair and Restoration Discussion Forum

radiograham · 12th Jul 2019, 1:20 am

I recently got this radio which is a mains/battery type. It is the first radio with a line cord I have seen in 40 years! The line cord is in poor condition and I wondered if anyone has ideas of the best way to replace this. I was thinking I could use an eliminator and run it in battery mode only or possibly fit a dropper to replace the linecord.

Graham.

Ed_Dinning · 12th Jul 2019, 8:09 pm

Hi Graham, I think one of the DD series did use an internal dropper, there should be space in the cabinet. Possibly even space for a proper power supply or a capacitive (heatless) dropper.

Ed

radiograham · 13th Jul 2019, 12:10 am

Hi Ed, my model is the early one, there were 3 models after with suffix a b c. mine is trader sheet 556. I was thinking about a capacitive dropper myself although i have never tried this technique myself, i think that the linecord is definitely going to be consigned to the bin! Graham.

Mike. Watterson · 13th Jul 2019, 9:06 am

External insulated & earthed piece of pipe with ceramic Wire wound resistors and/or capacitor inline on a cable to keep set original?
Also a replica battery pack to demo how much less interference on batteries. I only bother with "eliminators" on bench and never with a set with built in mains. On mains I'd check voltage on the 1H5G, DAF96 or DAF91 or equivalent that it's 1.32 to 1.38 V, ideally 1.35V at normal mains voltage (check it IS normal and not lower than usual) as recommended by the valve makers.
So the 8 to 12mA halfwave HT current will be "swamped" by the filament / heater currents, a capacitor dropper might be possible.
The rectifier seriously adds to the heater / filament current, hence many sets shortly after WWII used metal rectifiers and USA used 115V heater rectifier. I'd think they switched to external line cord due to internal heat issues as the original doesn't use it. Then they changed the rectifier.

I'd certainly use an external box or pipe for whatever voltage dropping arrangement is used to minimise risk to set and have it more original.

radiograham · 15th Jul 2019, 12:22 am

Hi, had to replace a lot of the mains wiring and the battery leads,will get it working on batterys first then go from there,also need a set of valves,thats going to be a bit of a search!.Found a date on speaker MAY1940. Graham.

Ed_Dinning · 15th Jul 2019, 7:26 pm

Hi Graham, there are plenty of equivalents to those types so you should get them easily and cheaply as they are not in demand for audio.
Even the earlier 1.4v octals (DF33 etc) are easy to get

Ed

radiograham · 16th Jul 2019, 12:11 am

Hi Ed, I meant a search in the attic TBH, but if they are cheap I might save myself the risk of falling off the ladder! Gone are the days when I used to go up in my slippers with a radio under my arm.

Graham.

crackle · 16th Jul 2019, 9:21 am

Were all the valves missing?

Mike

radiograham · 17th Jul 2019, 2:13 am

Yes they were.

radiograham · 27th Jul 2019, 10:15 pm

I have replaced all the wiring that was brittle and crumbling, also two of the electrolytics, one 8uf was completely dried out, this is only in circuit on batteries so I think this set was mostly used on mains, the other 16uf i tried reforming without success and the final 100uf 100 volt one was OK. Found a set of valves so am hoping to try it tonight. Most of the waxies were changed as well, some were more like resistors than capacitors! Hunts of course.

radiograham · 30th Jul 2019, 1:55 am

Well that's one I haven't seen before, had the set working on my eliminator, weak stations on MW. Decided to have a quick ferkle with the IF trimmers and blimey there is no screw in one of the trimmers, first IFT so I think it will have to come out to do anything about it. Usual thing can't get to nuts under chassis.

radiograham · 30th Jul 2019, 11:34 pm

Please ignore my last post about the ift,i looked at the circuit diagram and saw that ift1 has two windings wound on a dust iron? core but only the secondary has a trimmer across it.The second ift is conventional,i have never seen this arrangement before,was it just Decca that used it or were there other makers that did this?

radiograham · 9th Aug 2019, 1:17 am

This is working now but only on MW. i tried a DK91 by wiring it in temporary without success, have checked the micas in the osc circuit all OK. I think it is possibly a faulty wavechange switch, further investigation tonight.

12th Jul 2019, 1:20 am	#1
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Double Decca MB5 I recently got this radio which is a mains/battery type. It is the first radio with a line cord I have seen in 40 years! The line cord is in poor condition and I wondered if anyone has ideas of the best way to replace this. I was thinking I could use an eliminator and run it in battery mode only or possibly fit a dropper to replace the linecord. Graham.

12th Jul 2019, 8:09 pm	#2
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Double Decca MB5 Hi Graham, I think one of the DD series did use an internal dropper, there should be space in the cabinet. Possibly even space for a proper power supply or a capacitive (heatless) dropper. Ed

13th Jul 2019, 12:10 am	#3
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Hi Ed, my model is the early one, there were 3 models after with suffix a b c. mine is trader sheet 556. I was thinking about a capacitive dropper myself although i have never tried this technique myself, i think that the linecord is definitely going to be consigned to the bin! Graham.

13th Jul 2019, 9:06 am	#4
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Double Decca MB5 External insulated & earthed piece of pipe with ceramic Wire wound resistors and/or capacitor inline on a cable to keep set original? Also a replica battery pack to demo how much less interference on batteries. I only bother with "eliminators" on bench and never with a set with built in mains. On mains I'd check voltage on the 1H5G, DAF96 or DAF91 or equivalent that it's 1.32 to 1.38 V, ideally 1.35V at normal mains voltage (check it IS normal and not lower than usual) as recommended by the valve makers. So the 8 to 12mA halfwave HT current will be "swamped" by the filament / heater currents, a capacitor dropper might be possible. The rectifier seriously adds to the heater / filament current, hence many sets shortly after WWII used metal rectifiers and USA used 115V heater rectifier. I'd think they switched to external line cord due to internal heat issues as the original doesn't use it. Then they changed the rectifier. I'd certainly use an external box or pipe for whatever voltage dropping arrangement is used to minimise risk to set and have it more original.

15th Jul 2019, 12:22 am	#5
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Hi, had to replace a lot of the mains wiring and the battery leads,will get it working on batterys first then go from there,also need a set of valves,thats going to be a bit of a search!.Found a date on speaker MAY1940. Graham. Last edited by radiograham; 15th Jul 2019 at 12:26 am. Reason: misspelling

15th Jul 2019, 7:26 pm	#6
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Double Decca MB5 Hi Graham, there are plenty of equivalents to those types so you should get them easily and cheaply as they are not in demand for audio. Even the earlier 1.4v octals (DF33 etc) are easy to get Ed

16th Jul 2019, 12:11 am	#7
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Hi Ed, I meant a search in the attic TBH, but if they are cheap I might save myself the risk of falling off the ladder! Gone are the days when I used to go up in my slippers with a radio under my arm. Graham.

16th Jul 2019, 9:21 am	#8
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Double Decca MB5 Were all the valves missing? Mike

17th Jul 2019, 2:13 am	#9
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Yes they were.

27th Jul 2019, 10:15 pm	#10
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 I have replaced all the wiring that was brittle and crumbling, also two of the electrolytics, one 8uf was completely dried out, this is only in circuit on batteries so I think this set was mostly used on mains, the other 16uf i tried reforming without success and the final 100uf 100 volt one was OK. Found a set of valves so am hoping to try it tonight. Most of the waxies were changed as well, some were more like resistors than capacitors! Hunts of course.

30th Jul 2019, 1:55 am	#11
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Well that's one I haven't seen before, had the set working on my eliminator, weak stations on MW. Decided to have a quick ferkle with the IF trimmers and blimey there is no screw in one of the trimmers, first IFT so I think it will have to come out to do anything about it. Usual thing can't get to nuts under chassis.

30th Jul 2019, 11:34 pm	#12
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 Please ignore my last post about the ift,i looked at the circuit diagram and saw that ift1 has two windings wound on a dust iron? core but only the secondary has a trimmer across it.The second ift is conventional,i have never seen this arrangement before,was it just Decca that used it or were there other makers that did this?

9th Aug 2019, 1:17 am	#13
radiograham Hexode Join Date: Oct 2017 Location: Manchester, UK. Posts: 363	Re: Double Decca MB5 This is working now but only on MW. i tried a DK91 by wiring it in temporary without success, have checked the micas in the osc circuit all OK. I think it is possibly a faulty wavechange switch, further investigation tonight.