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Possible causes of tube preamp sputtering when warms up - with pick




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



Edits: 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12 08/08/12

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Topic - Possible causes of tube preamp sputtering when warms up - with pick - longtimequadowner 15:00:27 08/08/12 (6)

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