UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Trio 9R-59D receiver problems.

David G4EBT · 22nd Jan 2019, 1:06 pm

As to discharging the capacitors, lots of people will just put the blade of an insulated screwdriver across the live and neutral terminals, but it's much safer and more sensible, especially for the inexperienced, to make a simple discharge tool consisting of two insulated leads with a resistor in series, (typically 20K 5 Watt), so the charge decays away over a few seconds, rather than with a sudden crack and a flash. EG:

https://www.ifixit.com/Guide/Constru...arge+Tool/2177

The charge on the capacitors may have in any event decayed if the set's not been switched on for some hours or days, but it's always best to be on the safe side.

If you do decide to do the work yourself, before you think about re-stuffing the can, it would make sense for you to disconnect the three red wires and connect the + lead of each new capacitor to each of those three red wires, with the negative leads of the three new capacitors to the chassis. If that does cure the hum, I think you'd be wise to wire the new caps permanently and safely beneath the chassis, leaving the old can in place as I've mentioned before as an option. Opening up the can, removing the contents, resealing it and re-fixing it might be a step too far, but what you do with the set is a matter for you - as the saying goes, "you ride at your own risk" and on that, I've already sounded a note of caution as to potential hazards when working on the power supply. I'd draw your attention to the disclaimer at the bottom of the Forum page.

Suitable miniature Rubycon capacitors can be obtained from Farnell.

47uF 400V rated ones are 12.5mm diam x 30mm tall. They're 105 degrees rated, have a more than adequate ripple rating and long life, with a stated life of 7,000 - 12,000Hrs. They'd easily fit permanently under the chassis, but you should of course insulate the positive leads where they join the existing red wires, and the caps mustn't be left just dangling. (They would also fit inside the can).

https://uk.farnell.com/rubycon/400tx...831328?st=47uF Rubycon capacitors

The datasheet of this range of capacitors is here:

http://www.farnell.com/datasheets/23...025.1497772082

Hope that helps.

22nd Jan 2019, 1:06 pm	#118
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,765	Re: Trio 9R-59D receiver problems. As to discharging the capacitors, lots of people will just put the blade of an insulated screwdriver across the live and neutral terminals, but it's much safer and more sensible, especially for the inexperienced, to make a simple discharge tool consisting of two insulated leads with a resistor in series, (typically 20K 5 Watt), so the charge decays away over a few seconds, rather than with a sudden crack and a flash. EG: https://www.ifixit.com/Guide/Constru...arge+Tool/2177 The charge on the capacitors may have in any event decayed if the set's not been switched on for some hours or days, but it's always best to be on the safe side. If you do decide to do the work yourself, before you think about re-stuffing the can, it would make sense for you to disconnect the three red wires and connect the + lead of each new capacitor to each of those three red wires, with the negative leads of the three new capacitors to the chassis. If that does cure the hum, I think you'd be wise to wire the new caps permanently and safely beneath the chassis, leaving the old can in place as I've mentioned before as an option. Opening up the can, removing the contents, resealing it and re-fixing it might be a step too far, but what you do with the set is a matter for you - as the saying goes, "you ride at your own risk" and on that, I've already sounded a note of caution as to potential hazards when working on the power supply. I'd draw your attention to the disclaimer at the bottom of the Forum page. Suitable miniature Rubycon capacitors can be obtained from Farnell. 47uF 400V rated ones are 12.5mm diam x 30mm tall. They're 105 degrees rated, have a more than adequate ripple rating and long life, with a stated life of 7,000 - 12,000Hrs. They'd easily fit permanently under the chassis, but you should of course insulate the positive leads where they join the existing red wires, and the caps mustn't be left just dangling. (They would also fit inside the can). https://uk.farnell.com/rubycon/400tx...831328?st=47uF Rubycon capacitors The datasheet of this range of capacitors is here: http://www.farnell.com/datasheets/23...025.1497772082 Hope that helps. __________________ David. BVWS Member. G-QRP Club member 1339.