Can anyone offer some sage wisdom here? I bought a used MingDa MC34-b. Worked great for a couple months, then today - with no audio input going - it made a popping sound. I was not in the room, and when I went in there to see what happened. No lights on at all. Tubes dark, power switch dark.
It is likely that a power fluctuation of some kind occured, as there is storm going on here (not a thunder storm though). I took off the bottom plate, and there are no fuses that I can see. The only thing looking amiss in the case are two caps that were glued to the board, but aren't glued now. The connections (electrically) still look good to them, and they are not burnt or smelly, so I think that they are just floating there intact.
Would a blown tube totally shut power down to the whole amp?
Any ideas what is going on here?
Thanks!
It is likely that a power fluctuation of some kind occured, as there is storm going on here (not a thunder storm though). I took off the bottom plate, and there are no fuses that I can see. The only thing looking amiss in the case are two caps that were glued to the board, but aren't glued now. The connections (electrically) still look good to them, and they are not burnt or smelly, so I think that they are just floating there intact.
Would a blown tube totally shut power down to the whole amp?
Any ideas what is going on here?
Thanks!
If your amp is the same as my 34-b then there is a fuse in the IEC socket. It took me ages to realise that it was there, it is very well disguised and almost invisible at a quick glance.
Paul.
Paul.
The IEC (Inferior Electrical Connector) that accepts the power cord contains the miniature format cartridge fuse. That is most likely the only problem. It can be a challenge to get the fuse out the first few times until you train yourself to deal with what is a crappy design IMO.
There is a plated off cover section located in the bottom part of the connector. A small flat blade screwdriver will engage this cover right at the lip where it becomes the connector well. You have to try to pry outwards, the sidewall of the connector well just at the point it is about to turn 90 degrees and become the outer cover. There is a slight molded identification slot marking the place to pry. If this is undistirbed from the factory there is most likely a spare fast-blo fuse in the holder as well.
IMO Mei-Xing/Ming-Da should have used a smaller rated slo-blow fuse in their amps, and a soft start NTC resistor in the mains circuit to reduce turn on surge. The mains fuse in my own MC-34B has fried twice already from the chance closure of the power switch coinciding with the AC mains peak. A zero crossing SS switch would be a nice touch, but the NTC resistor and/or SB fuse is a much less expensive solution.
There is a plated off cover section located in the bottom part of the connector. A small flat blade screwdriver will engage this cover right at the lip where it becomes the connector well. You have to try to pry outwards, the sidewall of the connector well just at the point it is about to turn 90 degrees and become the outer cover. There is a slight molded identification slot marking the place to pry. If this is undistirbed from the factory there is most likely a spare fast-blo fuse in the holder as well.
IMO Mei-Xing/Ming-Da should have used a smaller rated slo-blow fuse in their amps, and a soft start NTC resistor in the mains circuit to reduce turn on surge. The mains fuse in my own MC-34B has fried twice already from the chance closure of the power switch coinciding with the AC mains peak. A zero crossing SS switch would be a nice touch, but the NTC resistor and/or SB fuse is a much less expensive solution.
Thank you for the replies! I had not looked there, but thought that would be really weird to have an amp with no fuse. I won't have time to get to it til tomorrow because my wife is taking boards today, but I suspect that is it. When It happened, I immediately thought fuse, but then couldn't find one (!)
I will let everyone know if that is it or not.
Again, Thanks for the help!
I will let everyone know if that is it or not.
Again, Thanks for the help!
That was it. What a weird place to put a fuse! But I'm here listening to my beautiful amp thanks to you guys. So Thanks! I was kind of half hoping it was a tube - but knew it wasn't probably what with total power failure and all.
I kind of am tempted to try out other tubes, I read and printed a thread about alternative tubes etc. Though I don't think I would want to try to alter the preamp circuits for 12v. That's a little above me. Anyway
Thank you.
I kind of am tempted to try out other tubes, I read and printed a thread about alternative tubes etc. Though I don't think I would want to try to alter the preamp circuits for 12v. That's a little above me. Anyway
Thank you.
Glad to hear you are back on the air! What speakers are you using with this amp?
I have rolled different tubes into my amp and am extremely happy with it now. I have vintage Mullard EL-34's in the outputs (internal re-bias adj. to 35 mA cathode idle current per tube necessary) and 6BK7A's as the long tailed phase inverters (outermost small tubes on the chassis layout). The sonic improvement was worthwhile and the output power is up by 10 watts more per channel to 28 RMS from the stock 18 watts with the 6P3P's measured both channels driven. I believe that I provided input to that page you looked at.
I have rolled different tubes into my amp and am extremely happy with it now. I have vintage Mullard EL-34's in the outputs (internal re-bias adj. to 35 mA cathode idle current per tube necessary) and 6BK7A's as the long tailed phase inverters (outermost small tubes on the chassis layout). The sonic improvement was worthwhile and the output power is up by 10 watts more per channel to 28 RMS from the stock 18 watts with the 6P3P's measured both channels driven. I believe that I provided input to that page you looked at.
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