rustling sound from one channel

paulf-2007

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I have a cheap Chinese kit valve amp, sounds great but after running it for a short while I got a rustling sound from one channel. This seems to happen each time I use it. I visited John Howes last week to discuss heating his museum rooms and workshop and on seeing the workshop realized he repairs valve amps, I had no idea and thought he just sold voxativ speakers. I explained the problem and he suggested swapping the valves, 6P3P, to see if the sound swaps channels, if not he would take a look at it. I swapped the valves next time it happened and it hasn't made the noise since after a long session. What could explain this.

 

awkwardbydesign

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Ah, it must be THAT cheap Chinese amp. Mine is working OK, with a bucking transformer to drop the mains voltage to 220-ish. However the Ming Da MC 84-C is better in the treble, so computer duties loom for the little SET. Changed the pot for an Alps 50k (I had one) and a set of prettier binding posts just arrived. Still on the original valves, resistors and caps for now, but will play with it some more and see if it improves.

Oh, and the courier sent me a bill for £21 for import duties. Bah!

 

paulf-2007

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I thought you had completely fucked it at some point by changing some of the parts. Mine actually sounds as good as any of my valve amps, so either my ears are shot or your speakers are crap:p

Ah, it must be THAT cheap Chinese amp. Mine is working OK, with a bucking transformer to drop the mains voltage to 220-ish. However the Ming Da MC 84-C is better in the treble, so computer duties loom for the little SET. Changed the pot for an Alps 50k (I had one) and a set of prettier binding posts just arrived. Still on the original valves, resistors and caps for now, but will play with it some more and see if it improves.Oh, and the courier sent me a bill for £21 for import duties. Bah!
 

awkwardbydesign

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Obviously your ears. :TheBird: The only thing I changed was the volume knob, plastic to metal. Would that make that make it sound hard? :D The pot was changed just a couple of days ago, made no difference. The other changes are yet to happen, only the side cheeks and bottom plate have been done. Oh, and the earth connection. Actually the Ming Da EL84 amp is pretty sweet sounding, it's surprised a few people.

The SET has lower gain/sensitivity than the Ming Da, I don't know if that makes a difference. And I've only compared them on the tweeters in my active system, early days yet.

 

paulf-2007

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sorry mate I must have you mixed up with someone else on here who bought the amp and then changed some of the parts and then it didn't work from one channel and the other channel the gain was down. I am using mine in my office system with CSS FR125RS single drivers and audax supertweeters, I also tried it with Adams then Heybrook Sextets in his second system and it sounded pretty good. As my main tri-amped speakers are being rebuilt by yours truly I might add I haven't tried it against my other two valve amps to see which two get the job. Just wondering if the parts in yours are the same as mine, the builder could have used whatever he could lay his hands on. Could you try it on your mids, may be a better comparison.

 

awkwardbydesign

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Lol, I wondered what you were on about! Thing is, I want it for HF duties, either that or the computer system. At only 8w (allegedly) it's underpowered for anything else. And I also wondered if the parts are the same as other versions. Siliconray sells it as a kit, but mine was ready built from here- http://www.ebay.co.uk/itm/121041038118?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I had it on the shelf under the TT, and it made my Decca hum, but weirdly it increased as the arm moved AWAY from the mains transformer!

We tried it at a bake off recently, and it sounded pretty good full range, but I've not done a direct comparison with the Ming Da. Maybe next time.

 

paulf-2007

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It was another wammer who had one but hadn't tried it, was thinking to give it to a relative until I suggested he listened to it first. He then said it sounded really good and then proceeded to change all the caps and fuck it up. I doubt he will come forward and admit it though.

 

paulf-2007

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breaking news................... working at John Howes place this week installing heat pumps in his museum ( mostly voight stuff and some wonderful old radiograms ) I mentioned to John about my rustling amp and he said to bring it along, so this morning John took a look at it, found two dry solder joints and a loose connection on a valve base, which he sorted, he checked the heater voltages and they were high as expected as its a 220v model. John fitted a resistor to sort that and then changed some caps to Russian paper in oil ones he uses. He showed me what was going on with the oscilloscope at different frequencies and there were some spikes in the normal mode it runs in and then in triode mode, much better, so decided to have reduced output and hopefully a better sound. He then sorted me out some nice valves, current ones are 6P3P and he found some 6L6GC. He was still testing it when we left for the day so tomorrow we will have a listen through the voxativs and then I will take it home and all for free, what a nice chap, but then he is getting a very good deal on the heat pumps.

 

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