David Eden WT800 amp, 2010 date, blows mains fuses

Sometimes after 1.5 hours originally , now sometimes soon after switch on , sometimes a bit later. Amp plate says 5A(T) for 240V use. Inside the IEC, is one non-blown 2A(T) in the active position, ah! the simplest of repair jobs, BUT No reported noises like magnetisation buzz or speaker noises , no smoke or smells. Owner uses the same cab and speaker wire with another amp ok. No blown fuses retained by the owner but reported to be blackened. 2A fuses passing 3A or so and then failing when asked to pass 4A say, but they will have fuse-wire breaks , not vaporisation and blackening. Tx torroid 0.8R or so per primary , measured cold, seems reasonable for

135mm diameter, 65mm high Tx. Not in a position to check the main caps yet , but no bulges. Any Eden usual suspects? PbF and RoHS stickers a-plenty
Reply to
N_Cook
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N_Cook presented the following explanation :

English punctuation would help understnd your giberish. B-)

And I think this has been said before. Are you a certified slow leaner?

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John G
Reply to
John G

At least the 25A triac is for mains-on soft start, not some sort of crowbar. Still not got to the caps yet. At least most of the schema for a version of these amps is out there

Reply to
N_Cook

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A bit like that famous tower in Pisa?

Reply to
Phil

Blackened pcb under R10 and R11 discoloured bands but reading 3R3 each ,pcb charring >30M DVM probing and goes from 20V Tx secondary to 1000uF 10V cap so unlikely a mains fuse KO Anodes of the valve go via ok MPSA92 to the ps , but may replace the 2x 160V

10uF caps in that area. Just leaves the 2x paralleled 3 , main caps 100V 10000uF. Other than separating and heating and measuring ESR (not necessarily related to self-curing internal flash-over) , nothing else left to explore? If its recovering interlayer discharge inside the Tx then can't do anything about that, any sort of tell-tale for that scenario? presumably add fuses would 10 amp blow before the 5A mains fuse with failing electro?) to the power rail secondaries
Reply to
N_Cook

Heavy engineering job as a solid block of snap-in 6 Jamicon , 85 deg C, LS, 809K(M) 100V 10,000uF. Presumably failing because the contact verticals between are filled with filled silicone rubber and hotmelt glue in the 2 central gaps and 85 deg C ratings. someone's internal view of similar amp

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12 1500W hot air gun to break the solder and binding of the most amenable set of Cs for wedges under then completed with a 100W soldering iron : 4oz board , wide traces and both sides of the pcb. No oily messes on the pcb but only one cap end is dry, 4 have an oily film and one has that plus drops. Expensive set of replacement 105deg C ones plus try and get some through ventilation, perhaps the replacements set at an angle to form a sort of duct and a small fan or as in line with the amp fan perhaps a duct only . And hope not an on-going internal Tx problem Cold ESR of each is good and warmed to whatever a minute of low setting hot air gun gets them to , no noticeable ESR change. I suppose the only test would be a current limited 100V supply , resistor and voltmeter to monitor implied leakage current and heating each cap .
Reply to
N_Cook

Cooked all 6 at 85 deg C, with thermometer in the middle of the block, for at least 30min and then applied 110 volt DC to each in turn, all charged up and held for 30 seconds or so and discharged normally and equally, while still at 85 deg C. But not too pleasant electrolyte smell in the room. Orientation of the caps was up the other way from useage and no vibration. I wanted one to show some obvious problem.

Reply to
N_Cook

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