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Old 9th November 2007, 04:22 PM   #1
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Default Help needed with Lectron JH 50 Amp

Hello,

I have a Lectron JH 50 amp which I love but recently has stopped working. Opening up I noticed that the power supply board under the power transformer has burnt out (see the attached picture). There is an ic chip with the number erased. I believe that this power supply board eventually fails. I have tried to contact the Swiss manufacturers of the Lectron JH 60 amps and Nick Doshi who I believe modifies these amps but have had no reply to my queries.

I believe that other members have had similar problems. Does anyone have a schematic for this amp? Or if anyone has a working replacement for the damaged board in question I would be glad to follow your design with kind permission. Any suggestions are welcome.

Many thanks.
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Old 9th November 2007, 08:25 PM   #2
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I really hate it when manufactures put power resistors on circuit boards like that without proper ventilation. But I'll bet that IC is a 555 timer for the relay.
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Old 9th November 2007, 10:39 PM   #3
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There is one for sale on FleaBay. You may want to ask the seller if he/she has a schematic...

http://cgi.ebay.de/ws/eBayISAPI.dll?...m=160177144324

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Old 11th November 2007, 04:53 AM   #4
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HollowState, yes you are probably right about it being a 555. It is a timer for the relay.

Jose, thank you for the info. Unfortunately the eBay seller does not have a schematic. I wonder if anyone has a copy of the old French magazine L'Audiophile. Apparently there was a schematic in issue #41 or 42 (I forget which). If someone has a copy I will be glad to purchase this.

An alternative is to redesign the whole power supply.
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Old 14th November 2007, 03:10 PM   #5
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Default I'm guessing

I think the resistors and relay are combined to form a slow turn-on circuit. The 55 delays the relay, which bypasses the resistors after a preset time. Maybe delays the B+ while the tubes are warming up.

Doesn't look that complex,. from what I can see.
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