Bush DAC10 lamp problem. - UK Vintage Radio Repair and Restoration Discussion Forum

joe-m60 · 14th Jun 2017, 5:55 pm

Recently picked up a DAC10 cheaply due to the back being damaged and in need of gluing in a few places, radio looks fine sat on shelf. I replaced the mains lead and the wax caps, with the new caps radio sounded much better and played much louder without distorting as it did before.

Only problem is after the radio has been on for about 30 min the lamps go out, changed lamps same result. This is my first attempt at working on a valve radio so would be grateful for some advice.

Station X · 14th Jun 2017, 7:02 pm

The correct lamps for this set are 3.5V, 0.15A. Not easily obtained, so I expect you fitted something different.

Is the voltage selector set correctly?

Is the shunt resistor (250R) measuring correctly?

When you say the lamps go out do they actually blow? Being in series I'd expect only one of the pair to fail.

joe-m60 · 14th Jun 2017, 10:44 pm

I found the correct lamps on ebay problem happens with original and new lamps, the shunt resistor is a 75 ohms resistor. The lamps do not blow they just stop working after 30 mins or so, I listen to this radio most days and the lamps go out after about 30 mins every time but the radio keeps working without problem.

Station X · 15th Jun 2017, 8:59 am

Same as the DAC90A arrangement then. Manufacturer's circuit shows 250R, but 75R is fitted. The fact that the radio carries on working without the lamps shows this resistor is OK.

If the lamps aren't working, then either one or both is open circuit, easily checked with a meter, or they're not making good contact with the holders.

Boater Sam · 15th Jun 2017, 9:24 am

I gave up trying to get the lamps to work reasonably and converted to LEDs.
Sam.

Voxophone · 15th Jun 2017, 11:04 am

Wasn't the lamp resistor on the DAC90A/DAC10 changed from 250R to 75R to stop the lamps being blown if the set was switched quickly off and on?

I restored a DAC90A recently which kept eating dial lamps and it turned out to be the UY41 rectifier. The lamps failed seconds after switch on and flashed brightly on and off - presumably due to arcing in the rectifier. Your problem sounds different but could be worth bearing in mind.

Liam

joe-m60 · 15th Jun 2017, 10:30 pm

I think the lamps are ok as they always come on again the next time the radio is used, I will check the lamp holders as they look quite dirty.

Hunts smoothing bomb · 16th Jun 2017, 8:45 am

Sounds like dirty connections or a dry solder joint that is going open circuit as the set warms up and then remakes again once the set has cooled down, I would check all joints on the wiring to the lamp holders, both soldered and any mechanical connections to chassis etc.

I would also remove the lamps and clean/spray the holders with Servisol/Deoxit or something similar and run the lamps in and out a few times on the thread to clean. Hopefully this will sort it.

Cheers

joe-m60 · 19th Jun 2017, 4:33 pm

The lamps don't seem to be a particularly good fit in the holders, but I gave the holders a good cleaning and made sure the lamps were seated as well as possible they are staying on all the time now, not very bright obviously but nice to have the radio working as it should, thanks for your advice.

Boater Sam · 19th Jun 2017, 4:53 pm

A lot will depend on the mains voltage at the time, a small increase will brighten the lamps quite a bit I found.
I am often surprised to find that the bulbs have burnt out on sets I acquire, I would think that glowing so dimly they would last for ever. Odd that often both are O/C seeing that they are in series.
At best they run at around 60% of rated load.

14th Jun 2017, 5:55 pm	#1
joe-m60 Retired Dormant Member Join Date: Jan 2016 Location: Wigan, Greater Manchester, UK. Posts: 6	Bush DAC10 lamp problem. Recently picked up a DAC10 cheaply due to the back being damaged and in need of gluing in a few places, radio looks fine sat on shelf. I replaced the mains lead and the wax caps, with the new caps radio sounded much better and played much louder without distorting as it did before. Only problem is after the radio has been on for about 30 min the lamps go out, changed lamps same result. This is my first attempt at working on a valve radio so would be grateful for some advice.

14th Jun 2017, 7:02 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Bush DAC10 lamp problem. The correct lamps for this set are 3.5V, 0.15A. Not easily obtained, so I expect you fitted something different. Is the voltage selector set correctly? Is the shunt resistor (250R) measuring correctly? When you say the lamps go out do they actually blow? Being in series I'd expect only one of the pair to fail. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

14th Jun 2017, 10:44 pm	#3
joe-m60 Retired Dormant Member Join Date: Jan 2016 Location: Wigan, Greater Manchester, UK. Posts: 6	Re: Bush DAC10 lamp problem. I found the correct lamps on ebay problem happens with original and new lamps, the shunt resistor is a 75 ohms resistor. The lamps do not blow they just stop working after 30 mins or so, I listen to this radio most days and the lamps go out after about 30 mins every time but the radio keeps working without problem.

15th Jun 2017, 8:59 am	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,289	Re: Bush DAC10 lamp problem. Same as the DAC90A arrangement then. Manufacturer's circuit shows 250R, but 75R is fitted. The fact that the radio carries on working without the lamps shows this resistor is OK. If the lamps aren't working, then either one or both is open circuit, easily checked with a meter, or they're not making good contact with the holders. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

15th Jun 2017, 9:24 am	#5
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush DAC10 lamp problem. I gave up trying to get the lamps to work reasonably and converted to LEDs. Sam.

15th Jun 2017, 11:04 am	#6
Voxophone Hexode Join Date: Oct 2015 Location: Sunderland, Tyne and Wear, UK. Posts: 340	Re: Bush DAC10 lamp problem. Wasn't the lamp resistor on the DAC90A/DAC10 changed from 250R to 75R to stop the lamps being blown if the set was switched quickly off and on? I restored a DAC90A recently which kept eating dial lamps and it turned out to be the UY41 rectifier. The lamps failed seconds after switch on and flashed brightly on and off - presumably due to arcing in the rectifier. Your problem sounds different but could be worth bearing in mind. Liam

15th Jun 2017, 10:30 pm	#7
joe-m60 Retired Dormant Member Join Date: Jan 2016 Location: Wigan, Greater Manchester, UK. Posts: 6	Re: Bush DAC10 lamp problem. I think the lamps are ok as they always come on again the next time the radio is used, I will check the lamp holders as they look quite dirty.

16th Jun 2017, 8:45 am	#8
Hunts smoothing bomb Octode Join Date: Oct 2005 Location: Wimborne, Dorset, UK. Posts: 1,407	Re: Bush DAC10 lamp problem. Sounds like dirty connections or a dry solder joint that is going open circuit as the set warms up and then remakes again once the set has cooled down, I would check all joints on the wiring to the lamp holders, both soldered and any mechanical connections to chassis etc. I would also remove the lamps and clean/spray the holders with Servisol/Deoxit or something similar and run the lamps in and out a few times on the thread to clean. Hopefully this will sort it. Cheers __________________ Lee

19th Jun 2017, 4:33 pm	#9
joe-m60 Retired Dormant Member Join Date: Jan 2016 Location: Wigan, Greater Manchester, UK. Posts: 6	Re: Bush DAC10 lamp problem. The lamps don't seem to be a particularly good fit in the holders, but I gave the holders a good cleaning and made sure the lamps were seated as well as possible they are staying on all the time now, not very bright obviously but nice to have the radio working as it should, thanks for your advice.

19th Jun 2017, 4:53 pm	#10
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush DAC10 lamp problem. A lot will depend on the mains voltage at the time, a small increase will brighten the lamps quite a bit I found. I am often surprised to find that the bulbs have burnt out on sets I acquire, I would think that glowing so dimly they would last for ever. Odd that often both are O/C seeing that they are in series. At best they run at around 60% of rated load.