XS-225 valve amp circuit.

[mschwilson]

Hi.
I recently bought an Advance Science XS-225R valve amplifier that was faulty.

The issue was that a linking wire had somehow got hot and melted causing the wire to short on the main-board.

It took out a large power diode and two smoothing caps, as well as a lump of circuit board and bits of track.

I've replaced everything I can, and even fired it up.
It goes through the motions, but when I turn the volume up to the first notch, all I get is a humm/buzz.

The problem I have is that there is a piece of track that I'm not sure if it is supposed to be connected to a particular component or not.

If it is supposed to connect, then that may be what is causing the buzz, if not, then at least I can start to look at component failure further afield.

My request is that if anyone has a curcuit diagram, or even better would be a picture of the underside of the circuit board, I would be eternally gratefull.

I know that this little amp may not warrant the interest for most of you guys and girls, but I just want to see it work.

Thanks for your time.

[blackieheil]

Hello

Send me your emailadress, and I'll send you some photos.

Stefan

[mschwilson]

Hi Stephan.

I've had a chance to look at the pictures, and do a comparisson with mine.
It appears that I've managed to correctly rebuild the tracks, so I think that my problem is a faulty component.

The buzz is far too loud to be transformer humm, and sounds more like the buzz you get from touching the inside of an RCA socket with something metal (not recommended ).

I'll have a hunt about, and if I find anything, I'll update here.
Cheers.

[Soonerorlater]

I know that this little amp may not warrant the interest for most of you guys and girls, but I just want to see it work.

I'm sure I'm not the only one who wants one of these Chinese cheapies as a donor for a pre-amp. Remote control and a USB input would be nice. It could house my RIAA phono stage when I finally get around to building it. The more I know about it's insides the better......


Fault finding can be very difficult if relevant info is sparse so the more you can provide the better.

A circuit schematic would be great. If the amp was wired point to point perhaps you could have drawn out the circuit yourself. Not so easy with a printed circuit board.

The issue was that a linking wire had somehow got hot and melted causing the wire to short on the main-board.

IMHO the issue is why the linking wire was conducting a current greater than it could safely take. (It's not always easy to see the difference between a symptom of a fault and its cause).

It took out a large power diode and two smoothing caps, as well as a lump of circuit board and bits of track.

By " taking out ", do you mean these components were electrically destroyed or just came off along with the lump. Also what voltage was each cap supposed to be able to take?

Brgds Bill

[mschwilson]

Hi Bill.

I used "taking out" to mean simply that they no longer functioned as intended, or at least not safe to use in my opinion.

The diode was blown lengthways (a crack all the way down the side) and the track has risen off the board in a number of places, as well as a huge (in terms of standard hole size on your average circuit board) hole in the board.

Although the caps may have been electrically sound, they had burn marks on them and some of the plastic wrap was melted off making them dangerous next to the bare wire links.

I'm afraid I have no idea about amplifier design, or the time to take my repairs much beyond the "fix the obvoius" stage, much as I would like to. But I really wanted to fix this little amp mainly cos my fiancee bough it for me as she thought it looked "pretty", which it actually does.

I've managed to get it to work on both channels, but with a huge buzz (which does not increase with volume) on the left, and bleed from this on the right.
I think a component is faulty, but I'm going to leave that to someone else to sort out.

I'll be sticking it on Ebay soon.

[mschwilson]

I meant ot add this in case it's of any use to anyone.



http://www.diyaudio.com/forums/attac...1&d=1323376251

[Soonerorlater]

I'll be sticking it on Ebay soon.

Probably for the best

[RS232]

I have the same hibrid amp with exactly the same fault (don't know about the buz because I have not yet fixed it)
I was looking for causes of the failed diode ( 1N5408 ) and melted cables and this is what i found out.
The melted cables are from the heaters power supply
The 2 6N1 tubes need 600 +/-50mA each
The 2 6n15 tubes need another 650 +/-30mA each
The cable is so thin that there is no way it can take 2.5A of current
The diode (1n5408 ) is only rated at 3A
Going to replace the 2 4700uf x50V capacitors and the burned cables and let you guys know.

Ric

PS. This hibrid amp is just not worth the £49.99 they are asking right now on ebay (it was £249) it will not last 2 hours of continuous operation

[RS232]

Just to add that that I made a small mistake...
The 2nd valve is a 6P15 and not a 6N15.
The 6P15 needs 740 to 860mA for the heater.
No wonder that the diode and cables go up in smoke.

Ric

[mschwilson]

Hi Ric.

Thanks for the extra info on this, and I'm looking forward to knowing what you did to sort yours out.

I'm not going to do anything else with mine, as I really don't do amps, and with the voltages that valves/tubes work with, I think it's best until I can follow someones lead.

Cheers for now.

Si