Music angel XD-SE EL34

[OXAUDIO]

Originally Posted by Rullknufs

I've been thinking of buying a Music Angel XD 500 MKIII Amplifier.
It will cost me around 700-750$. It is two years old, not used the last year. Tubes have been running 150-200 hours and one of the tubes at the back is pulsating a little slower than the others. What does that mean?

I'm not familiar with the XD500mkIII, and, indeed it's been several years since
I serviced/repaired a Music Angel Amplifier, but, having said that, if by 'pulsing',
you mean oscillating, surely no valve in an amplifier should oscillate.
This could indicate poor grounding, faulty capacitors, or other problems.
Having just downloaded the circuit diagrams of the XD500mkIII, I'm a little
puzzled to see that 28mV @ 105kHz is present at the speaker terminals-almost 6 times the level at 121hz. Seems wrong to me!

[OXAUDIO]

Originally Posted by JackM11

Thanks everyone for sharing the schematic and information. My EL34 is the same as Kippy's. After a bias adjustment, I set the bias to be about 40ma. The resistor is 22 ohm(one for each El34 tube) so the reading is about 0.88V across it. I guess I have one weak tube as the voltage was 0.67v before but the bias adjustment took care of it. The amp sounds pretty good.
I noticed that the version posted by Erick is very different. Some resistors values are in hundred ohms instead of thousands ohms.
I noticed that the ground pin on the power receptacle is not wired. Should I wire it to the chassis? Can I get better performance if I remove the 6E2 magic eye tubes? I am new to this so any suggestions would be appreciated.

As far as I know, removing the Magic Eye Tubes will not make any difference to the amplifier's performance, but I would definitely connect the Earth Pin of the power receptacle to the chassis metalwork. A short lead to a tag fitted under the nearest fixing screw should be adequate. Obviously a 3-wire mains lead should then be used. In the U.K. at least, a double pole mains switch would be considered better than the single pole one usually fitted by the makers.

[Rullknufs]

Originally Posted by OXAUDIO

I'm not familiar with the XD500mkIII, and, indeed it's been several years since
I serviced/repaired a Music Angel Amplifier, but, having said that, if by 'pulsing',
you mean oscillating, surely no valve in an amplifier should oscillate.
This could indicate poor grounding, faulty capacitors, or other problems.
Having just downloaded the circuit diagrams of the XD500mkIII, I'm a little
puzzled to see that 28mV @ 105kHz is present at the speaker terminals-almost 6 times the level at 121hz. Seems wrong to me!

So, you suggest it's a bad idea to buy it?
I've asked to guy for a film of the amplifier when up and running.
What is the problem when looking at the circuit diagrams? Is it a bad amplifier?

[Rullknufs]

YouTube - M2U00065

That's the amplifier up and running.
What do you think?
I didn't see any difference between the two, to be honest. Do you?

Edit: A friend of mine said it looked like a "Magic Eye". After googling a little it seems like it's just cosmetic, built into the tubes. If i can't stand with it i just guess i have to change tubes. But if one pulsates slower than the other, is it the "Magic Eye's" fault or something else? :O

Edit 2: One think i came to think of. Maybe it depends on the music being played. If there's more stuff going on in the left channel it obviously needs a little more power. And then the left "eye" blinks more than the right one, and vice versa.
Or is it a faulty tube or even the amp? Maybe it could be the amp sending the signal slower/weaker to one of the channels?

[Svein_B]

Originally Posted by Rullknufs

So, you suggest it's a bad idea to buy it?

The amp is a reasonably good one.
The price of around $700 may however seem a bit high, especially if some tubes are close to burning out.

You can buy a new MA with KT88 for $600 including shipping (but excl. your country's VAT). The general opinion is that this is a better amp, especially if you roll some of the small signal tubes.

Svein

[Rullknufs]

Originally Posted by Svein_B

The amp is a reasonably good one.
The price of around $700 may however seem a bit high, especially if some tubes are close to burning out.

You can buy a new MA with KT88 for $600 including shipping (but excl. your country's VAT). The general opinion is that this is a better amp, especially if you roll some of the small signal tubes.

Svein

Well, it's my 1 year old Harman Kardon HK3490 + 1000kr (which is around 145$). It seems like he will drive to my place with the amp so i can quality check it. I think we will split the fuel costs which would be around 400-450kr for me. If i sell my HK3490 today i could get maybe 3500. The price has dropped quite much recently, and with my student discount i can buy one for 3450 at a large scandinavian seller. Maybe i could only get around 3000 for it since the price has dropped so incredibly much since i bought it.
So, if we say my amp is 3000 and then i pay 1000 and 450 for fuel. That's around 650$

If i buy somthing from outside of EU i have to pay the 25% swedish Moms. And then there's the toll fee and such... Would end up at around 1000$ or so probably.

[OXAUDIO]

I stand corrected, Rullknufs. Didn't realise that you were speaking of the Magic Eye (or
'Cat's Eyes' as the schematic calls them) As far as I can tell from the You Tube video, they are behaving as I would expect such indicators to perform-i.e. responding to the
variations in sound level in the music, which is of course in stereo. If a sine or square wave signal of the same amplitude was fed into each channel, then the indicated level,
subject to the usual component tolerances, would be the same for both channels, and
the display from the 'eyes' would be steady.
As Svein_B says though, the price still seems a bit high, if a new KT88 equipped MA can be had for $600 +VAT(in the U.K. that would make it $720, or approx.
4930 Swedish Kroner- with 25% tax in Sweden, though, the total price would be $750.
At any rate you'll have to be the judge of which is the better buy

[Rullknufs]

Well. If i buy the KT88 stuff (can you please link to it?) i guess i will have to ship it from outside Sweden. I don't think my parents would like that at all since they're suspicious to everything.
But if you link it it will take a look at it.

[OXAUDIO]

I don't have a link to the M.A. XD-SE (KT88) amplifier. The circuit is essentially similar to the EL84 version. They are probably available from China or Hong Kong on E Bay. As noted in my earlier reply
I was simply quoting from Svein_B's post. I do have some printed information
somewhere about the amplifier, most, if not all of which, came from other posts
on this forum 3 or 4 years ago. From memory, a similar circuit to the EL84
version(based on the classic Williamson design) is used, with either triode or Ultra Linear o/p stage configuration selectable via a front panel switch.