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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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26th Feb 2019, 5:14 pm | #1 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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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
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26th Feb 2019, 5:19 pm | #2 |
Heptode
Join Date: Jan 2008
Location: Birchington Kent, UK.
Posts: 596
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Re: Trio 9R-59DS Mechanical Filter problem / question
Could this be the infamous 'tin whisker' effect on the inside the screening can?
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Regards Pete |
27th Feb 2019, 9:38 am | #3 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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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 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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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
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28th Feb 2019, 5:39 pm | #5 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,935
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Re: Trio 9R-59DS Mechanical Filter problem / question
Looks like it had some sort of spillage inside it.
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1st Mar 2019, 9:17 am | #6 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,015
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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! |