Murphy B40D intermittant sparking? - UK Vintage Radio Repair and Restoration Discussion Forum

murphyv310 · 30th Jun 2007, 8:57 pm

Hi.
My old and trusty B40D is giving me nightmares.
It has over the past 6 months given a very intermittant fault. The set can run OK for 30mins then you hear sparking inside and crakling in the speaker.
I have replaced both EZ90 rects replaced the audio valve with an ECL82 (replaced and rewired base) cleaned all valve bases and examined caps, joints, cables, switches etc. This fault only happens about once a month, but the set is at eye level and is really heavy so the next time it comes down will have to be the last, any ideas??
Trevor

Sean Williams · 1st Jul 2007, 9:03 am

If it is anything like the last B40D I owned, I would be suspecting a wiring issue - Mine had glorious rubber "insulated" wiring - I ended up replacing the lot (not a job to be taken lightly!)

Good Luck!

dave walsh · 1st Jul 2007, 10:47 am

I'll be interested in any comments. I have aqquired a B40 from a very nice lady in Plymouth who's son used up all the valves thirty+ years ago and she has looked after it ever since! I haven't seen it yet as it went directly to my mother-in laws place in Bicester. When she spotted it she asked "what's that safe doing in the garage?" I keep asking her if she's found the key yet? I think the phrase is built 'for' [not just like] a battleship. They were clearly designed to take a direct hit from a shell and not the kind you find on the beach-for those who know the Bob Newheart records.
As they were made by the Murphy Co I shall just think of it as an aluminium [rather than wood] member of the family group. Dave

XTC · 1st Jul 2007, 5:08 pm

I've got a B40. Mine's got the B8B valve line up (EF22 and pals) and fortunately, it's all PVC wired. I haven't had to mess with it yet. It's certainly heavy, but the handles are nicely placed and I find it less awkward to handle than an AR88.

Intermittent faults are always a pain in the neck. It could be an insulation problem as Saun suggests, or a cap breaking down, or maybe arcing across a valve base. However, you've had a good look for signs of arcing and burning and turned up nothing.

I'd be inclined to run the set with the cover off in a darkened room and try and narrow down the arcing that way. Now, if the fault develops after 30 minutes or so, it suggests it's somehow heat related and running it with the cover off might not show the fault.

The last time I saw anything like this with a radio, was a domestic set in which one of the smoothing caps was breaking down and reforming for a short time.

Pete.

murphyv310 · 1st Jul 2007, 7:37 pm

Hi.
I was lucky today and the set showed up the fault, I removed the cabinet and the problem was still there. One of the EZ90 bases was sparking, so after I replaced it all seems to be well, only time will tell.
Thanks for the input.
Trevor

30th Jun 2007, 8:57 pm	#1
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Murphy B40D intermittant sparking? Hi. My old and trusty B40D is giving me nightmares. It has over the past 6 months given a very intermittant fault. The set can run OK for 30mins then you hear sparking inside and crakling in the speaker. I have replaced both EZ90 rects replaced the audio valve with an ECL82 (replaced and rewired base) cleaned all valve bases and examined caps, joints, cables, switches etc. This fault only happens about once a month, but the set is at eye level and is really heavy so the next time it comes down will have to be the last, any ideas?? Trevor __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

1st Jul 2007, 9:03 am	#2
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,517	Re: Murphy B40D intermittant sparking? If it is anything like the last B40D I owned, I would be suspecting a wiring issue - Mine had glorious rubber "insulated" wiring - I ended up replacing the lot (not a job to be taken lightly!) Good Luck! __________________ Engineers make things work and have spare bits when finished

1st Jul 2007, 10:47 am	#3
dave walsh Dekatron Join Date: Jan 2006 Location: Ramsbottom (Nr Bury) Lancs or Bexhill (Nr Hastings) Sussex. Posts: 5,817	Re: Murphy B40D intermittant sparking? I'll be interested in any comments. I have aqquired a B40 from a very nice lady in Plymouth who's son used up all the valves thirty+ years ago and she has looked after it ever since! I haven't seen it yet as it went directly to my mother-in laws place in Bicester. When she spotted it she asked "what's that safe doing in the garage?" I keep asking her if she's found the key yet? I think the phrase is built 'for' [not just like] a battleship. They were clearly designed to take a direct hit from a shell and not the kind you find on the beach-for those who know the Bob Newheart records. As they were made by the Murphy Co I shall just think of it as an aluminium [rather than wood] member of the family group. Dave

1st Jul 2007, 5:08 pm	#4
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Murphy B40D intermittant sparking? I've got a B40. Mine's got the B8B valve line up (EF22 and pals) and fortunately, it's all PVC wired. I haven't had to mess with it yet. It's certainly heavy, but the handles are nicely placed and I find it less awkward to handle than an AR88. Intermittent faults are always a pain in the neck. It could be an insulation problem as Saun suggests, or a cap breaking down, or maybe arcing across a valve base. However, you've had a good look for signs of arcing and burning and turned up nothing. I'd be inclined to run the set with the cover off in a darkened room and try and narrow down the arcing that way. Now, if the fault develops after 30 minutes or so, it suggests it's somehow heat related and running it with the cover off might not show the fault. The last time I saw anything like this with a radio, was a domestic set in which one of the smoothing caps was breaking down and reforming for a short time. Pete.

1st Jul 2007, 7:37 pm	#5
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: Murphy B40D intermittant sparking? Hi. I was lucky today and the set showed up the fault, I removed the cabinet and the problem was still there. One of the EZ90 bases was sparking, so after I replaced it all seems to be well, only time will tell. Thanks for the input. Trevor __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member