Trio 9R-59DS Mechanical Filter problem / question - UK Vintage Radio Repair and Restoration Discussion Forum

snowman_al · 26th Feb 2019, 5:14 pm

The Trio was going well until an hour ago.
Cleaned and tidied the fascia etc. Tidied the mains wiring and moved the 150 volt regulator and fit the thick wire mod to the oscillator HT.

All tests well, 10 minutes or so, then had to move the chassis, with the set on of course, to be rewarded by a cacophony of loud crackles and noise.
Typical bad valve connection I thought, so straighten them up and switch on again, still the same then I notice a smell and find the first mechanical filter can very hot to touch? Expletive!
Swap V4 'just in case' - just the same.

So nothing to loose, I took the filter apart to see what was wrong inside. Expecting a melted mess, but apart from lots of gunk and a black spot on the internal plastic shield, nothing obvious... So I've cleaned it very carefully, and put it back temporarily (without the can) and switched on and it works fine again

Any ideas or suggestions. Should I worry and replace it, if I can find one, or move on?

Alan

g4aaw pete · 26th Feb 2019, 5:19 pm

Could this be the infamous 'tin whisker' effect on the inside the screening can?

Jon_G4MDC · 27th Feb 2019, 9:38 am

The only thing that will make it hot enough to be smelly is too much current through the primary winding between R8 / C9 and the Anode of V2.

Something made V2 draw that current. Check R4 and R5 are good.
Make sure C5 and C6 are not leaky?

snowman_al · 28th Feb 2019, 4:27 pm

Well good progress on this.
Pete gets the prize too, not exactly 'whiskers', but certainly can corrosion.

Having cleaned and replaced the first filter and can, I ran the set for more than 8 hours and subjected it to lots of movement. All worked fine.
I checked round V2 as Jon suggested, but all appears to be well there.

As I had not really paid much attention when I dismantled the first filter (MF1), I was expecting a failed coil back then, I thought it better to make sure the other HT connected filter (MF2) was OK. Good job I did.

The pictures are of the second filter. You can see the green corrosion on the shield and inside the can. (Not sure if it is nickle or copper?) That is at the HT hot side too.
Not so much 'gunk' in this one, but much the same as the first regarding the 'green'. I suspect the 'green' slowly bridges the HT on the pins to the earthed can. Either by humidity (?) or a 'flake' moving as you flex the set during repair or operation perhaps.
Then, judging by the crackling noises, I suspect now the HT arcs to the can, heating it and making the smell? There was evidence of tracking / melting on the shield in the first can.

The 'green' needed silver polish to remove it from the can. I tried solvents, but nothing touched it. They are nice and shiny inside now though!

Alan

HamishBoxer · 28th Feb 2019, 5:39 pm

Looks like it had some sort of spillage inside it.

Jon_G4MDC · 1st Mar 2019, 9:17 am

That's a good find - I think your theory is spot on - damp makes some salts from corrosion and these conduct and break down when subjected to some vibration. It is a very good fix.

I always thought a lot was being expected of the insulation in those transformers which look more suited to transistor circuit Voltages!

26th Feb 2019, 5:14 pm	#1
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Trio 9R-59DS Mechanical Filter problem / question The Trio was going well until an hour ago. Cleaned and tidied the fascia etc. Tidied the mains wiring and moved the 150 volt regulator and fit the thick wire mod to the oscillator HT. All tests well, 10 minutes or so, then had to move the chassis, with the set on of course, to be rewarded by a cacophony of loud crackles and noise. Typical bad valve connection I thought, so straighten them up and switch on again, still the same then I notice a smell and find the first mechanical filter can very hot to touch? Expletive! Swap V4 'just in case' - just the same. So nothing to loose, I took the filter apart to see what was wrong inside. Expecting a melted mess, but apart from lots of gunk and a black spot on the internal plastic shield, nothing obvious... So I've cleaned it very carefully, and put it back temporarily (without the can) and switched on and it works fine again Any ideas or suggestions. Should I worry and replace it, if I can find one, or move on? Alan Attached Thumbnails __________________ Never Leave Well Enough Alone...

26th Feb 2019, 5:19 pm	#2
g4aaw pete Heptode Join Date: Jan 2008 Location: Birchington Kent, UK. Posts: 595	Re: Trio 9R-59DS Mechanical Filter problem / question Could this be the infamous 'tin whisker' effect on the inside the screening can? __________________ Regards Pete

27th Feb 2019, 9:38 am	#3
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Trio 9R-59DS Mechanical Filter problem / question The only thing that will make it hot enough to be smelly is too much current through the primary winding between R8 / C9 and the Anode of V2. Something made V2 draw that current. Check R4 and R5 are good. Make sure C5 and C6 are not leaky?

28th Feb 2019, 4:27 pm	#4
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Trio 9R-59DS Mechanical Filter problem / question Well good progress on this. Pete gets the prize too, not exactly 'whiskers', but certainly can corrosion. Having cleaned and replaced the first filter and can, I ran the set for more than 8 hours and subjected it to lots of movement. All worked fine. I checked round V2 as Jon suggested, but all appears to be well there. As I had not really paid much attention when I dismantled the first filter (MF1), I was expecting a failed coil back then, I thought it better to make sure the other HT connected filter (MF2) was OK. Good job I did. The pictures are of the second filter. You can see the green corrosion on the shield and inside the can. (Not sure if it is nickle or copper?) That is at the HT hot side too. Not so much 'gunk' in this one, but much the same as the first regarding the 'green'. I suspect the 'green' slowly bridges the HT on the pins to the earthed can. Either by humidity (?) or a 'flake' moving as you flex the set during repair or operation perhaps. Then, judging by the crackling noises, I suspect now the HT arcs to the can, heating it and making the smell? There was evidence of tracking / melting on the shield in the first can. The 'green' needed silver polish to remove it from the can. I tried solvents, but nothing touched it. They are nice and shiny inside now though! Alan Attached Thumbnails __________________ Never Leave Well Enough Alone...

28th Feb 2019, 5:39 pm	#5
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,931	Re: Trio 9R-59DS Mechanical Filter problem / question Looks like it had some sort of spillage inside it. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

1st Mar 2019, 9:17 am	#6
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Trio 9R-59DS Mechanical Filter problem / question That's a good find - I think your theory is spot on - damp makes some salts from corrosion and these conduct and break down when subjected to some vibration. It is a very good fix. I always thought a lot was being expected of the insulation in those transformers which look more suited to transistor circuit Voltages!