Marconi 559 hum - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

PaulR · 2nd Sep 2011, 7:20 pm

I was only able to find a 32uf so I put this in parallel with the existing 10uf and it made a big difference. The 50hz can still be heard faintly and felt a little on the speaker cone but it is much improved. I might try increasing the other smoothing caps. The rectifier's maximum reservoir capacitance is 32uf. Will it "see" both C29 and C31 and hence the total of these should be 32uf maximum or can I increase C31 without worrying about C29?

Thanks

paul

PaulR · 2nd Sep 2011, 7:47 pm

Thinking about it I suppose that increasing the reservoir capacitor wouldn't help as it isn't a rectified 100Hz ripple that is the problem so reducing the amount of that ripple isn't relevant.

ms660 · 2nd Sep 2011, 8:41 pm

I would would have thought you would have hum with the output valve plugged in and warmed up with the rectifier unplugged due to the nature of the biasing arrangements in the set.
No rectifier in means no DC on the transformer center tap, but possible stray AC, this line feeds negative bias to the grids of the valves.

Visit the link below for an insight into the ancient art of back biasing if it is unfamiliar and look at the wave forms shown in this link.

http://www.aikenamps.com/BackBiasing.html

If you are familiar then ignore the link.

Hope this is of some use.

Lawrence.

PaulR · 3rd Sep 2011, 11:01 am

Thanks Lawrence, that is most interesting.

I took the electrolytic can apart this morning and substituted the 33uf for the 10uf for C21 and the hum is much less now. Shorting the 10uf I took out across C31 made no difference so I have left that alone and reassembled the can.

I am now going to put it back together again and see what it sounds like. Many thanks to all who have helped.

Paul

smiler411 · 3rd Sep 2011, 11:07 am

Could you try removing V4 and see if the hum disappears. If it does then the hum is not caused by the output stage or output transformer.

I think you should look at V4 for the cause of your hum as it disappears when you remove C25.

PaulR · 4th Sep 2011, 1:53 pm

Removing V4 doesn't reduce the hum. It is within acceptable limits now, and although it would be good to reduce it further I think it is as good as I am going to get. I have put it back into its case and I have to say it sounds very well indeed. I tried connecting a CD player to the gram inputs and the reproduction was excellent.

Thanks all.

Paul

PaulR · 20th May 2016, 12:00 pm

Just a very late addition to this thread. I bought a Marconi 557 which has a very similar chassis and the same smoothing arrangements. The remains of the leads to the smoothing can were apparent in this one and the Trader sheet has more detail on where the leads should go. I guessed this on the 559.

When I compared them I had put some of the leads in the correct position according to the circuit diagram but at the other end of a lead than was originally the case. Putting them as originally intended has more or less eliminated the hum.

The 557 has restored very well electrically, having been found in a garage but I think the case may need completely stripping and giving the Danish oil treatment.

Paul

turretslug · 20th May 2016, 10:06 pm

Good to see that this perplexing snag was sorted in this classic set- I reckon this series represents an object lesson in what constitutes a "proper" radio! Sturdy steel chassis and real wood cabinet, and tuning by gears, rather than string.

PaulR · 21st May 2016, 9:29 am

Yes they are beautifully made sets and sound very good. I gave the tuning caps in both of them the dishwasher treatment and they responded very well. Getting the caps out of the pitch filled can was not easy but that is part of the fun with pre war EMI sets!

I really want the radiogram version to add to the collection but I doubt that SWMBO would react well.

Paul

turretslug · 23rd May 2016, 4:13 pm

I'd heard of the dishwasher trick for tuning capacitors but, despite it's having been recommended on this forum with its track record of sage advice, I was uneasy- there was enough suggestion of "April Fool!" to deter me! However, when I got a 559 with a particularly filthy VC, I gave it a go. The chassis was coated with thick grey felted dust that lifted and brushed off to reveal almost factory-fresh steel-work and components but the tuning assembly was a different matter. Someone had liberally coated (indeed, I got the impression that they were under some sort of incentive to use as much as possible) the whole works with 3-in-1 oil (one of my most detested substances). The whole lot was covered in thick, dark, filthy, sticky, gummy grime with that acrid pong that always makes my heart sink, including fixed and moving vanes- why the heck would anyone do that?? There were crusty, corroded dark green puddles of yuk down and under all the brass parts. Thinking I've nothing to lose, I removed the assembly and put it in the dishwasher on a short, mild program in deference to the Paxolin vane supports and it came up factory-fresh. Brilliant.

Yes, it's given me a hankering for others in the series- it would be nice to find a Marconi 538/HMV 469 or even a Marconi 561/HMV 650, though the latter is a bit OTT and there's not a lot of use for a 12-5m SW band nowadays, whether for 11m or 41.5MHz TV sound!

PaulR · 23rd May 2016, 4:29 pm

The 557 and 559 are the only sets I have done this to. The tuning cap is quite easy to get out as long as you can melt the solder on the earthling straps. Also there is no fiddly tuning cord to worry about.

I told a friend who is an electronics engineer about this and he said they regularly clean modern equipment in a dishwasher. In fact he seemed to be saying that withstanding a dishwasher was some sort of construction standard.

turretslug · 24th May 2016, 11:42 am

You're not kidding about the earthing braid- my weapon of choice for valve kit, Antex X25 with broad bit wouldn't touch the frame connections, next, a Weller TCP with "9" heat grade bit was little better, finally the little-used Weller W100 with "8" bit worked a treat. Not helped by the cramped access.

jmedley · 25th May 2016, 1:16 pm

Hello Paul
Having read this thread re your Marconi "559" I do not think that your chassis is a 559. I cannot envisage that the manufacturer would have knowingly fitted what seems to be the chassis of the Marconi 851 (HMV 651) that uses octal valves. Trader sheet 350
Someone may have changed the chassis or you have a complete 851 with the wrong model plate on the cabinet

?
I have recently completed a Marconi 851 and posted it on this forum with some pictures, I hope this will help
Jim

jmedley · 25th May 2016, 1:47 pm

Hello again Paul
I have looked at earlier threads and it appears that some 559s do use octal valves, however the trader sheet 605 clearly shows it to use 7pin valves

Marconi have such a plethora of models from 1934 up to 1940 I can't see that they would have missed the chance to have another model I.D which would have been the correct procedure.
It could have caused problems if dealers ordered valves etc for the 559

Maybe other members here could add info re their 559

Thanks
Jim

PaulR · 25th May 2016, 2:05 pm

Hi Jim

I thought I had replied to your posting but it seems to have got lost in the aether! I wonder whether they "morphed" one model into the next one as new valves became available and the model numbers didn't keep up.

I was interested to read that the speaker in yours needed attention. The one in mine had been replaced by a PM one with the coil retained as a smoothing choke and the one in the 557 is degrading at the bottom where the cone attaches to the frame. I have repaired it using masking tape fixed with Evostik . It seems that the speaker cone material may be a weak point.

Here https://www.vintage-radio.net/forum/...ad.php?t=74987 is a link to the restoration of mine and here https://www.youtube.com/watch?v=NsXnhd_CT0M is one to it working.

turretslug · 25th May 2016, 2:44 pm

Presumably, the general transition from 4 volt B7 to 6.3 volt IO was happening around this time that happened to be partway through the 559 production cycle. In marketing and PR terms, it's not a particularly "sexy" sort of detail, so perhaps it wasn't worth mentioning or changing a model designation. A brochure might proclaim the presence of a magic eye or a gas-filled stabiliser, perhaps, but more arcane detail doesn't really excite the man in the street. There's a 559 and an HMV499 here, both with 4 volt B7 lineup (apart from 6.3 volt IO magic eyes- I think these latter were initially a US development anyway, so perhaps not surprising).

WW2 and consequent US technology and manufacturing domination seemed to have made 6.3V and IO literally "international" but sets like this imply that this trend was well under way before then.

2nd Sep 2011, 7:20 pm	#61
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum I was only able to find a 32uf so I put this in parallel with the existing 10uf and it made a big difference. The 50hz can still be heard faintly and felt a little on the speaker cone but it is much improved. I might try increasing the other smoothing caps. The rectifier's maximum reservoir capacitance is 32uf. Will it "see" both C29 and C31 and hence the total of these should be 32uf maximum or can I increase C31 without worrying about C29? Thanks paul

2nd Sep 2011, 7:47 pm	#62
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Thinking about it I suppose that increasing the reservoir capacitor wouldn't help as it isn't a rectified 100Hz ripple that is the problem so reducing the amount of that ripple isn't relevant.

2nd Sep 2011, 8:41 pm	#63
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Marconi 559 hum I would would have thought you would have hum with the output valve plugged in and warmed up with the rectifier unplugged due to the nature of the biasing arrangements in the set. No rectifier in means no DC on the transformer center tap, but possible stray AC, this line feeds negative bias to the grids of the valves. Visit the link below for an insight into the ancient art of back biasing if it is unfamiliar and look at the wave forms shown in this link. http://www.aikenamps.com/BackBiasing.html If you are familiar then ignore the link. Hope this is of some use. Lawrence.

3rd Sep 2011, 11:01 am	#64
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Thanks Lawrence, that is most interesting. I took the electrolytic can apart this morning and substituted the 33uf for the 10uf for C21 and the hum is much less now. Shorting the 10uf I took out across C31 made no difference so I have left that alone and reassembled the can. I am now going to put it back together again and see what it sounds like. Many thanks to all who have helped. Paul

3rd Sep 2011, 11:07 am	#65
smiler411 Tetrode Join Date: Apr 2008 Location: Rhondda Cynon Taff, Wales, UK. Posts: 88	Re: Marconi 559 hum Could you try removing V4 and see if the hum disappears. If it does then the hum is not caused by the output stage or output transformer. I think you should look at V4 for the cause of your hum as it disappears when you remove C25.

4th Sep 2011, 1:53 pm	#66
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Removing V4 doesn't reduce the hum. It is within acceptable limits now, and although it would be good to reduce it further I think it is as good as I am going to get. I have put it back into its case and I have to say it sounds very well indeed. I tried connecting a CD player to the gram inputs and the reproduction was excellent. Thanks all. Paul

20th May 2016, 12:00 pm	#67
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Just a very late addition to this thread. I bought a Marconi 557 which has a very similar chassis and the same smoothing arrangements. The remains of the leads to the smoothing can were apparent in this one and the Trader sheet has more detail on where the leads should go. I guessed this on the 559. When I compared them I had put some of the leads in the correct position according to the circuit diagram but at the other end of a lead than was originally the case. Putting them as originally intended has more or less eliminated the hum. The 557 has restored very well electrically, having been found in a garage but I think the case may need completely stripping and giving the Danish oil treatment. Paul

20th May 2016, 10:06 pm	#68
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Marconi 559 hum Good to see that this perplexing snag was sorted in this classic set- I reckon this series represents an object lesson in what constitutes a "proper" radio! Sturdy steel chassis and real wood cabinet, and tuning by gears, rather than string.

21st May 2016, 9:29 am	#69
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Yes they are beautifully made sets and sound very good. I gave the tuning caps in both of them the dishwasher treatment and they responded very well. Getting the caps out of the pitch filled can was not easy but that is part of the fun with pre war EMI sets! I really want the radiogram version to add to the collection but I doubt that SWMBO would react well. Paul

23rd May 2016, 4:13 pm	#70
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Marconi 559 hum I'd heard of the dishwasher trick for tuning capacitors but, despite it's having been recommended on this forum with its track record of sage advice, I was uneasy- there was enough suggestion of "April Fool!" to deter me! However, when I got a 559 with a particularly filthy VC, I gave it a go. The chassis was coated with thick grey felted dust that lifted and brushed off to reveal almost factory-fresh steel-work and components but the tuning assembly was a different matter. Someone had liberally coated (indeed, I got the impression that they were under some sort of incentive to use as much as possible) the whole works with 3-in-1 oil (one of my most detested substances). The whole lot was covered in thick, dark, filthy, sticky, gummy grime with that acrid pong that always makes my heart sink, including fixed and moving vanes- why the heck would anyone do that?? There were crusty, corroded dark green puddles of yuk down and under all the brass parts. Thinking I've nothing to lose, I removed the assembly and put it in the dishwasher on a short, mild program in deference to the Paxolin vane supports and it came up factory-fresh. Brilliant. Yes, it's given me a hankering for others in the series- it would be nice to find a Marconi 538/HMV 469 or even a Marconi 561/HMV 650, though the latter is a bit OTT and there's not a lot of use for a 12-5m SW band nowadays, whether for 11m or 41.5MHz TV sound!

23rd May 2016, 4:29 pm	#71
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum The 557 and 559 are the only sets I have done this to. The tuning cap is quite easy to get out as long as you can melt the solder on the earthling straps. Also there is no fiddly tuning cord to worry about. I told a friend who is an electronics engineer about this and he said they regularly clean modern equipment in a dishwasher. In fact he seemed to be saying that withstanding a dishwasher was some sort of construction standard.

24th May 2016, 11:42 am	#72
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Marconi 559 hum You're not kidding about the earthing braid- my weapon of choice for valve kit, Antex X25 with broad bit wouldn't touch the frame connections, next, a Weller TCP with "9" heat grade bit was little better, finally the little-used Weller W100 with "8" bit worked a treat. Not helped by the cramped access.

25th May 2016, 1:16 pm	#73
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	Re: Marconi 559 hum Hello Paul Having read this thread re your Marconi "559" I do not think that your chassis is a 559. I cannot envisage that the manufacturer would have knowingly fitted what seems to be the chassis of the Marconi 851 (HMV 651) that uses octal valves. Trader sheet 350 Someone may have changed the chassis or you have a complete 851 with the wrong model plate on the cabinet? I have recently completed a Marconi 851 and posted it on this forum with some pictures, I hope this will help Jim

25th May 2016, 1:47 pm	#74
jmedley Rest in Peace Join Date: Jun 2012 Location: Milton Keynes, Buckinghamshire, UK. Posts: 109	Re: Marconi 559 hum Hello again Paul I have looked at earlier threads and it appears that some 559s do use octal valves, however the trader sheet 605 clearly shows it to use 7pin valves Marconi have such a plethora of models from 1934 up to 1940 I can't see that they would have missed the chance to have another model I.D which would have been the correct procedure. It could have caused problems if dealers ordered valves etc for the 559 Maybe other members here could add info re their 559 Thanks Jim

25th May 2016, 2:05 pm	#75
PaulR Dekatron Join Date: Oct 2003 Location: Southport Lancashire, UK. Posts: 3,236	Re: Marconi 559 hum Hi Jim I thought I had replied to your posting but it seems to have got lost in the aether! I wonder whether they "morphed" one model into the next one as new valves became available and the model numbers didn't keep up. I was interested to read that the speaker in yours needed attention. The one in mine had been replaced by a PM one with the coil retained as a smoothing choke and the one in the 557 is degrading at the bottom where the cone attaches to the frame. I have repaired it using masking tape fixed with Evostik . It seems that the speaker cone material may be a weak point. Here https://www.vintage-radio.net/forum/...ad.php?t=74987 is a link to the restoration of mine and here https://www.youtube.com/watch?v=NsXnhd_CT0M is one to it working.

25th May 2016, 2:44 pm	#76
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: Marconi 559 hum Presumably, the general transition from 4 volt B7 to 6.3 volt IO was happening around this time that happened to be partway through the 559 production cycle. In marketing and PR terms, it's not a particularly "sexy" sort of detail, so perhaps it wasn't worth mentioning or changing a model designation. A brochure might proclaim the presence of a magic eye or a gas-filled stabiliser, perhaps, but more arcane detail doesn't really excite the man in the street. There's a 559 and an HMV499 here, both with 4 volt B7 lineup (apart from 6.3 volt IO magic eyes- I think these latter were initially a US development anyway, so perhaps not surprising). WW2 and consequent US technology and manufacturing domination seemed to have made 6.3V and IO literally "international" but sets like this imply that this trend was well under way before then.