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Wow AA sure has some detailed asylum categories - never been in this one before!I got a heavily upgraded Ming DA MC7R that has malfunctioned from day one. It sounds great when first turned on, but after about 15 minutes cuts in and out while sputtering loudly - very loudly.
Attached is a pic - in case anyone can spot components known for high failure rates.
I will take it to a shop locally as I have no technical skills at all - this guy works on tube and vintage tube gear so they say, I'm sure he has to get running a lot of their vintage trade-ins. If I can gather some suggestions here though, it probably can't hurt.
This was a somewhat expensive upgrade and until it sputters and scares me out of my chair, it actually sounds pretty good even with the Chinese tubes. Yes, I have swapped the entire set of tubes with my other non-upgraded MC7R. Sadly, that wasn't it.
What could start to fail as it warms up - 15 minutes? The transformers weren't even getting warm at that point...
PS this is the so-called "extreme" mod from RAM - click link for details
Further update - switch rectifier tubes, still happens. Timed it, takes 20 minutes to start crackling. But, so far - it happens in episodes - crackles for 10-15 seconds, then stops. I expect episodes will get closer together - am monitoring...
Further update - damn this thing sounds good. 30 minutes play time, two sputtering episodes. When not sputtering, seems perfect.
Hmmm... One hour of listening - still only two outbursts of popping, but at all times there is a low level static on one channel. Not enough to interfere with listening, but easily heard when no music. Static at same level when volume is at zero.
Ouch - major outburst at 1 hour 10 mins, popping in/out rapidly - sounded like a machine gun for a good 15 seconds. I think it did so even when source selector was changed but will have to verify that "next time".
Ok - another outburst of machine gun fire for 20 seconds at 1 hour 30 minutes of listening - confirmed, popping / machine gun fire continues even when source selector is changed. That can't be good.
Thanks in advance
Religion is the world's oldest profession
Edits: 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12Follow Ups:
Thanks for the input guys, in talking a bit with the tech also it sounds like this is not a major issue, just some detective work, I feel much better about saving this piece as it does sound very good between "episodes"...
Religion is the world's oldest profession
Can you not send it back to Ram Labs to make it good? It seems that they should stand by their work. good luck, Dak
Just for reference, here's the stock unit
Religion is the world's oldest profession
Cold solder joint, loose tube pin in the socket, grossly microphonic tube.Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
It sputters after the resistor is warmed and expanded. It is likely one of those grey metal oxide resistors. RAM should use wirewound Mills resistors. I would have the unit upgraded with better resistors. Looks like RAM just did a cap swap.
.
I've heard that type of noise with cold solder joints as well, and any component that was breaking down might do it. There's a solid state rectifier in there too.
In any case it really doesn't matter. He doesn't have the skills to troubleshoot or repair it so it has to go to tech.
I would definitely not use it until it is fixed as it could damage a speaker.
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