• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Music Angel XD-850MKIII 300b integrated amp

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Ok, I know I shouldn't have but I bought this amplifier. I am intelligent but uneducated in electronics except for the basics.

When this thing arrived at my home (in Israel) I plugged it into 220V electrical outlet. We have standard European system here. I'm an American but at least I understand that much. I bought this device to use in Israel.

It worked great, sounded nice for about 3 weeks. And then a fuse blew. I replaced the fuse and it istantly blew again. So, being the smartass, dumbass that I am I put foil over the burned fuse to see what would happen. The amp played beautiful music but then smoke began coming out of the power transformer. (at least that's what I think it is) I disconnected it immediately from the electricity and no one in Israel seems to have a clue about anything but transistors.

Should I buy a new transformer online and simply solder it into place with the same connections?

Thanks for your help.
 
To me, it sounds like one of two things. Crappy designed rectifier tube with poor quality control when made, and/or the first power filter capacitor is breaking down under stress. Is the Music Angel amplifier you are talking about one of those chinese or korean made amps from hong kong? I have never had anything good to say about those things. Other people swear up & down that they are the best amps ever, and other people say they are just junk. The "junk" people have said that they will play for a few weeks or maybe a year at best, then something happens. What category do you fall in? 🙄
 
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Is this the amp with DCC90 (3a5) into 2a3 into 300b?

A few people bought these in London, and they sound great - this is an all-DHT amp and an excellent tube combination.

But friends here also had problems. There must be threads about this amp - it would be worth rebuilding it but you'd have to give it to someone really familiar with tubes. It has an unconventional biasing system for the 3a5 for starters. Unfortunately I believe it has PCBs which are harder to tweak than point to point wiring.

If it were mine I'd use an outboard filament supply for the first two stages and swap the 3a5 for something like an 01A or ideally a 26. But all this would mean you were pretty familiar with what to do.

Andy
 
300B Music Angel Naked

Music Angel Naked 002.jpg
 
mjaymc, be careful with insides of your amp - be sure to go all of the safety instructions - u can find some guidelines at this forum. I've read that their is enough current stored inside tube amp components to kill a human being.
 
Thanks guys. I've got the RCA complete electronics school on disk. It may take me a year to get through it. Quite a bit more difficult than building a PC.

Building a PC , isn't hard at all , let me tell you , making a regulated power supply is much TOUGHER then building a PC , and that's honestly , easy .
But anyway , i'm not to comment on you , i'm quite bad , can't design a circuit properly .

But who cares ? I'm a student in secondary school and they do not teach anything beyond how to make a moisture sensor .
Sure , i might be just plain talking , i built myself a 8W guitar amp 😉
 
Ok, I know I shouldn't have but I bought this amplifier. I am intelligent but uneducated in electronics except for the basics.

When this thing arrived at my home (in Israel) I plugged it into 220V electrical outlet. We have standard European system here. I'm an American but at least I understand that much. I bought this device to use in Israel.

It worked great, sounded nice for about 3 weeks. And then a fuse blew. I replaced the fuse and it istantly blew again. So, being the smartass, dumbass that I am I put foil over the burned fuse to see what would happen. The amp played beautiful music but then smoke began coming out of the power transformer. (at least that's what I think it is) I disconnected it immediately from the electricity and no one in Israel seems to have a clue about anything but transistors.

Should I buy a new transformer online and simply solder it into place with the same connections?

Thanks for your help.

Have you open up the chassis to do a visual check yet? (do not plug in or turn on the amp when you are inspecting it especially if you don't understand tube electronics!) If you saw smoke, then you should be able to see burned or charred components, I am guessing it is one of the resistors or capacitors, those are simple to replace and cost practically nothing.

It seems you have/had a short somewhere but it is unlikely to be the transformer imo (I think you meant the power and not the output transformer, no?) Anyway, the circuit itself is pretty simple, and you should read Lampizator's article here. He does a few mods and tube swaps to bring the best of the amp. So don't give up on it just yet...

Good luck!
Jaz
 
I had an 845 chinese amp, did just the same thing, it turned out to be the solid state rectifiers in the psu, so check the psu first, filter caps and rectifiers.

once the diodes were replaced, worked a treat.

chinese amps are great, they just need a little attention at first.
 
Hi,

I've got a true 300b amp, they're single ended class-A commonly powered with a rectifier such as 5U4 or even a luxury 274B, an improved diode-tube version, but a DIRECT-heated type, wich means a lower vallue for the 1st. cappacitor to extend a C.'s life expectations (Doesn't handle HIGH start-up current peaks that well!),.. or maybe a (damaged) C. shortcut's or something, a reason to smoke! What other tubes are involved? Maybe a shortcut, trouble is.. It's hard to measure shortcuts WHILE a tube is in operation.. 🙁

In my case a 274B rectifier (or anything else with LARGE plates for that matter, combined with CORRECT cap.'s!) has indeed improved some bass "punch", making up for lousy design and/or transformer losses in a cheapo Chinese amp. featuring 2x GU-50 ('mini' 300B's) and 2x 6SJ7's, never got it to actualy smoke however.. @.@ ..
 
I brought this(Music angel 300b) amplifier yesterday(29-august-2015), would like to know the reason for a sound(thup) coming from speaker after switching off the amplifier on the right channel, since I brought it from China, I am not to able to get it back to for servicing.
 
I had an 845 chinese amp, did just the same thing, it turned out to be the solid state rectifiers in the psu, so check the psu first, filter caps and rectifiers.

once the diodes were replaced, worked a treat.

chinese amps are great, they just need a little attention at first.

'Little attention first.......'--Such as a full re-design you mean, in a lot of cases!😀
Thats what I ended up doing anyway.....🙂
 
I am new on the repairs\re-design, possible to get an insight about the PSU, caps and rectifiers, I am ready to get my hand dirty..
And one more thing observed today is one of the tube is glowing purple on the top, is that anything related to sound(thup) coming from speaker after switching off the amplifier on the right channel?
 
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