Author Topic: Mengyue/Music Angel Mini tube amp 6P1 pp  (Read 48883 times)

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Offline ian444

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Mengyue/Music Angel Mini tube amp 6P1 pp
« on: March 30, 2009, 11:34:20 PM »
Just wondering if anyone else has one of these amps and enjoys it? I love the sound of this one. More realistic "live" sound than any of my other amps. It has no mods, all I did was rework the PCB and put a 0.47 ohm resistor in parallel with one of the heater circuits to get the voltage down a bit to match the other heater winding. But it sounds great, and I am wondering if it is the output tubes partly responsible as I have tried other tubes, but they don't have the "magic" of the original. The original tubes are 6P1 made by the Beijing ELVT factory as far as I can tell, and sound better than the Shuguang which sound better than the Russian 6P1's (or maybe a longer break-in period is required). My other amps are Chinese EL34 pp, 6L6GC pp, EL34 se and gainclone built into NAD 3020. The little tubes with less power output really sing. I also noticed that the current through the preamp 6N2 tubes is low, about 1mA and they are biased in a fairly non-linear region, but it sounds very nice to my ears. Surely, many of these amps have been sold? Also I am running 2 x 8 ohm speakers in parallel per channel and the amp has no problems driving them. They are so cheap, its cheaper than buying the components. The schematic is nothing fancy either, very traditional, with paraphase inverter and trimpots. Anyone else got one of these? And like it? If nothing else, this amp could be a good base for tweaking, it really does sound nice just as is though.

Ian.

Offline ole

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #1 on: March 31, 2009, 08:21:59 AM »
Sure looks cute. Where did you get it?

Ole

Offline yeo

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #2 on: March 31, 2009, 02:09:06 PM »

is the sp1 el84?

yeo


Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #3 on: March 31, 2009, 03:25:42 PM »
The 6P1 is a 9-pin valve like the EL84 but rated at 12W dissipation, has a maximum anode voltage of 250V, and about half the gm. EL84 is 14W and 300V max. They have a different pinout too. 6P1 is electrically closer to a 6AQ5.

I got the amp from ebay, do a search on "6P1".The amp in the top pics uses the same PCB and valves, and I am guessing the trannies are identical too. One of my friends has one so I could check that out. The one I bought is in the bottom pics and are harder to find now. There were variants of it with EL84 valves too. It cost me AUD$220 when the dollar was good against the USA dollar, now it looks like the cheapest you can get one is around AUD$260 with surface (sea) shipping, but you may have to wait to get a cheap one. They come with no earth wire to the chassis and the various electrical imperfections thrown in are free :)

Ian.

Offline assendor

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #4 on: March 31, 2009, 09:36:34 PM »
Hello Ian,

I got some experience with Music Angel, but with the 845 amp.

Now you are correct, they are really really cheap.
The one you got there is REALLY cheap.. :)

Bought my amp the 845 ONLY for rebuilding it completely, and did so.
Wanted to get some more experience in Tube amps, didn't have any clue at all.
Oh that is not all true, bought a kit something K-502 11BM8 something push and pull amp, but it was so extremely simple and easy to make there where no learning in the process.
The sound also was much related to the size of the transformers and price..

Anyway back to the MA 845.
Out of the box it sounds terrible, or it sounds better than regular commercially available A/B amps, in most cases, but still horrible..  :D
Actually I didn't even listen to mine before starting to tweak and rebuild it.
I just tested that there was sound first on left channel, and then in right channel. It was OK.

After rebuilding it quite a lot, following some others drawings and idea's, it sounded still bad, cause the Chinese tubes in preamp and driver stage was completely HORRIBLE.
I changed these, and it sounded fantastically good, but didn't have any power before distortion...

After a lot of investigation I found this amps power supply was completely different than the one they made just weeks earlier.
There even where missing some of the chokes pictured at eBay.. ERR:.

So the power supply had to be rebuilt too...
Now it got better, but the power transformers got so hot I could barely touch them..
So i got me a variable Isolation transformer and adjusted it to 220v exactly. Still just as hot..  >:( >:(

Just left it like that, and used it for quite some time, rebuilt all the circuitry inside a couple a times more...
Finally it got very nice, and this still with the originally supplied 845tubes, or not them, but some of the same type I ordered, since the ones with the amp was completely messed up.
AND it was not during transport, it was either done at the factory, or it was done when they carelessly tested the amp... Anyway, I denied taking these damages at the transporter insurance, since it WAS NOT A TRANSPORT DAMAGE...
Well so then they denied paying anything, and I bought my own tubes.. Just as well, I AM not a LIAR and a thief, so it was just fine.

The sound from this amp is nothing short of fantastic, after all tweaks and fixes, especially if compared to the price.
BTW, I used only 6H8C tubes both in pre and driver stage, these had plenty of gain.
OF course changed resistors and power supply changes to make these fit to different current drawn.

After a lot of adjustments and finalizing the output noise was lower than 1mv at 8ohm output terminals.
4ohm tapping was useless, even on 4ohm speakers and had NO power AT ALL. 8ohm output was doing fine from 6-8ohm speakers.

Later it cough fire, and I'm glad the building it was in didn't burn to the ground... Or got badly messed up.
IT smelled in there for weeks, if not months.
HAD to repaint the walls to get rid of the smell.. :)

Now in the later day's I think the cause for the total meltdown has been found.
Since they had rebuilt the amp, since the tweak drawings I had was made...
The filaments where somehow differently connected, so they had another voltage level to ground.
This most likely caused it to fail.
I'll check this further, as a friend of mine has one like it. And of course this one also tries to melt down from time to time... For now his PCB-traces has just been blown away instead.
There are of course NO FUSES anywhere inside the amp. So complete meltdown is the fuse.

Like you say, it is really cheap, cheaper than to buy all the parts and build it.
When it comes to my amp, well... I could have gotten a pretty good set of Lundahl transformers for the price I paid including shipping. Now this is the only things usable on this MA amp, the output trans..

Wisdom, yes lots of lessons learned, and got much more experience with tube amps and datasheets for such things.
It was worth it, absolutely worth it. For a beginner that want's to learn it's perfect.
IF YOU ARE AWARE OF THE HIGH VOLTAGES INSIDE, AND TAKE PRECAUTIONS THEREAFTER.

BTW, the schematic for my amp didn't match real life at all.
Maybe they have improved, after they have absolutely didn't.. or they ran out of parts, and just redesigned it to fit the available part list?? It's hard to say.
For some business is business, and they're only concerned for the income that particular day  :-\
What was it that caused the world financial crisis again.. ;) Oh yes, no plans for the next day, so they're not alone.
How wonderful.

-Jonas

Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #5 on: March 31, 2009, 10:58:58 PM »
Jonas,

Interesting comment on the GFC :)

You are right its a great way to learn. Unfortunately I bought even more Chinese amps to learn more, and in hindsight if I put all that money into one good kit amp, I might have a better amp, but less understanding, and less experience of the different sounds of different amps. Plus I would not have known where to start, and maybe build 2 or 3 amps to find what I wanted, so maybe unfortunately is not the right word. Its a long road :)

My amp didn't sound very good when I first turned it on, but then it got better slowly, and then one channel started crackling, so I reworked the PCB a couple of times and made the filament voltages right and its been great ever since. I also discovered 240V in Australia is way too high for any of these amps and 220V is good, so I bought a mains conditioner box that has a switch for 220, 230 or 240V. I had problems with 2 other amps too, one blowing tubes (expensive), and the other one was getting too hot and it got a full rebuild, and circuit changes and lots of extra ventilation holes. They all sound pretty good now but the Mengyue is the best for realistic sound, it's like the band is in the same room sometimes. I have had no problem with the Chinese 6L6GC equivalent, but when that amp (Ming Da) started blowing up tubes I eventually fixed it by doing a SimpleEL84 diyparadise conversion, and used 2 Chinese and 2 TAD tubes in it as that was all I had left, 1 Chinese and 1 TAD in each channel. It looks like the bias pot for fixed bias was playing up in hindsight. It now uses a 6N2 pre tube with both halves in parallel and is very clean sounding with plenty of power, much better sound than before and bass went lower too. I like the 6N2 tube, but I have not heard many others, and hearing good things from it in 2 different amps which have different sound makes me think it is not the weakest link.

What I am thinking is that this Mini amp sounds real good with no tweaks, and its cheap. But because of the way it is built with the PCB, it is cumbersome and time consuming to try different components, as the 6 valves need to be removed and then the PCB lifted with all the wires still connected, not good... so it really needs to be rebuilt point to point, which might be a good first project for a lot of people interested in valve amps. I don't want to do that right now as I am building another amp with the same valves but using the SimpleEL84 diyparadise scheme so I need it as a comparison.

Hope my house doesn't burn down in the meantime Jonas, that is scary!

Ian.

Offline assendor

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #6 on: April 01, 2009, 01:56:19 AM »
Hello Ian,

IT is interesting to experiment with Tube amp, and all electronics for that matter.

6N2 seems to be exactly the same as 6N2P Russian tube, isn't this correct?
This is a similar or much the same tube as 12AX7, only different filament.

It is recommended to let the tubes break in at least 24hours or so.
Many of the Russian tubes have already had it's break in time, I don't know for sure why this is,
probably a little endurance test they have on them, to see they hold they're data for a certain time.
Most of them tubes are to be used in nuclear equipment, so it is probably desirable they actually work...

It would be seriously interesting to hear your opinions of the 6N2P-EV or 6N2P-V compared to the Chinese 6N2.

When it comes to the 6P1P-EV Russian tubes, what is it that you find different sounding with these tubes in your amp, compared to the Chinese Beijing ELVT, and Shuguang 6P1?
What is it that you like less with the Russian ones?

The original preamp/input/driver tubes 6N3...??  Is it a output beam tetrode??
Are they interchangeable with 6P1P  ?? No these are bigger..?
6N1P is similar maybe? Amplification 35 and This 6N3 has 55.. ERR:.

ERR it does not seem to have any substitution...
Here is a link to find some information obviously:
http://giaime.altervista.org/china.html

-Jonas
 

Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #7 on: April 01, 2009, 05:41:51 PM »
Yes Jonas, Chinese 6N2 seems exactly the same as the Russian 6N2P from the datasheets. The curves in the datasheets are a bit similar but definitely not the same as a 12AX7, but I am no expert in reading these curves :)

Here's an interesting link on Russian 6N1 and 6N2, scroll down a bit.
http://www.arrakis.es/~igapop/russianotes.htm#6N1P%20/6N2P%20How%20to%20use%20them

I don't have any 6N2P on hand, if I did I would drop them in. From memory, the Russian 6P1P-EV had less detail, less high frequency. I will put them back in today and have another listen...

The adds on ebay for this amp, some say they come with 6N3, but they don't, they come with 6N2. Look at this one, auction ending in an hour or so, if no-one bids it will go for US $176.
http://cgi.ebay.com/MA-6p1-6AQ5-Valve-Push-Pull-Integrated-Tube-Amp-BK_W0QQitemZ180339873505QQihZ008QQcategoryZ3280QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
It says 6N3 driver tubes, but if you scroll down the page and click on the pic with the valves in the box, I think I can see "6N2" printed on one of the pre tubes. Those 6P1 tubes in the pic are what I call the Beijing ELVT valves, they have the octagonal mica plates and the logo is a small star with 3 stripes either side similar to a winged-C logo. These are the ones I am running and I like a lot. The Shuguang 6P1 valves have a different logo, a big star stretched sideways, and round mica plates. But I think Shuguang owns Beijing ELVT, and it is difficult to get any solid information as to who sells what and which valve came from where etc.

This is the mains conditioner box I mentioned before, with a switch to set the output to 220/230/240V.
http://www.apc.com/resource/include/techspec_index.cfm?base_sku=LE600I&tab=models
Cost about AUD $80 to $100. Might be of interest to someone...

Ian.

Offline assendor

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #8 on: April 01, 2009, 07:23:01 PM »
Hello Ian,

interesting link you had there about the Russian tubes.

When it comes to your link to that amp on eBay, no ONE did bid anything, and the starting price was US $39.00
Why won't you get it for this? Do they have lowest price reserve something??
No One did bid,,  Well.. they have saturated the marked to a degree with these amps.

Think I forgot to mention something important about the Music Angel 845 I got... Or had. :)
OF Course I ripped out everything that had to do with internal signal cables, switches and volume stuff.
I tried to use the signal cables, ,,, Oh.. i would rather have used anything of metal connecting it, they where extremely horrible.

Russian Tubes, I like them a lot.
6N6P is a interesting tube too. Some find the sound a bit laid back, or a bit dull... Guess it depends on the rest of your system.

When my MA was tweaked to the end, it was not dark sounding at all, not on any speakers.
The Teflon FT-3 caps HAD to be in bypass with whatever caps used in signal path though.
IF not, dark.
My Coral Flat8 have never sounded so brilliant and "airy" in the top end, as they did on that amp.
Not before, not after, and probably will not either.. :) Guess they will, but they sounded beautiful on that particular amp.
So I guess it depends on a lot of things, if the Russian tubes sound dark or bright.. or perfect.. :)

There is no reason in datasheets why they should have any Roll-off in top end.
I guess when they are relabeled to another "brand", they sound less dark to people...  :D :D :D

Now that is life, and so it will be forever and ever.
BUT NOT FOR ME!!  ;D ;D ;D

Try to give them a second chance and let them break in for a while, maybe you could check if they liked a different biasing?
It is not impossible they need a different current to sound "well".

I ran my 6H8C on 5-6mA bias and 238volts(SRPP this is). When to use American tubes, they where recommended biased at 2-3mA if I'm not mistaken.. ?
So it might be the same with those 6N1P, that they could need a lower value cathode resistor??

IF you try to run a higher bias, remember to check the supply voltage, in my amp this was determined only by some resistors, so it was a pain when something was changed in the current drawn by the driver stage, or in the Preamp stage.

-Jonas

Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #9 on: April 02, 2009, 02:40:51 AM »
They build a "reserve price" by using high shipping and insurance rates, so if you had bid on that amp, and won the auction at US$39, it would have cost you US$176 with the cheapest shipping option which is by sea (about 4 weeks to deliver). I don't know why they do it that way...

I haven't had time to experiment with load lines yet, but I see that my amps using the 6N2 pre tube are both biased at very low current, something around 0.8mA for the Mengue and even less for the Ming Da (pic attached). Looks like a strange place to have the load line but sounds really good...I will work it out one day. I did try increasing the current through the 6N2's in the Mengyue by using a smaller anode resistor but found no improvement so put it back.

Didn't get time to try the Russian 6P1P today, but definitely this weekend! It is possible that the Chinese 6P1 might sound too bright in an amp that sounds good with the Russian 6P1P, so it gets back to the synergy theme again. Will get back and let you know how the Russian tubes sound. Maybe it was just an accident that the Mengyue sounds so good to me, or maybe there was some dude who really knew what he was doing when he chose all the components, valves, transformers and circuit? Or maybe my ears...

I have some EH EL34's in an SE amp and they sound pretty good to me, cannot fault them, so I'm not against Russian tubes by any means. That amp is another work in progress, but having a new amp to build and a Mojo and some other projects and recently working 6 days a week, time was scarce, but now a few days off! :)

Ian.

Offline assendor

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #10 on: April 02, 2009, 04:57:47 AM »
Hello Ian,

You cannot increase the current much in the tube lowering that resistor value..
That only causes the tube to work with a different voltage over it, higher actually.
IT is possible that it can be beneficial to reduce this resistor value, along with reducing the value of the Cathode resistor, this to maintain much the same voltage above the valve as before.

The reduced resistance of the Anode resistor will most likely not change the sound much, only limit it's possible voltage swing before clipping. YES and also increase power dissipation due to higher voltage across the valve.

Try to decrease the value of the Cathode resistor. This will lift the valve's Grid/Cathode voltage closer to Zero, and will increase the bias current trough the tube.

OF course you should not overdue this either, you will also get limitations here, but as you can see from the diagram drawing load lines and such, you will not change everything completely then.
It is smart to do a check first.
The tube does normally  not like to have voltage swings forcing it to swing close to zero GRID/Cathode voltage.
So don't overdue it.  :)

Experimenting is a lot of fun.. :)

-Jonas

Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #11 on: April 03, 2009, 02:49:36 AM »
Jonas, I put the 6P1P-EV in, let it run on radio all day for extra break in. The missus says its better than the Beijing 6P1, more raw sound she says. I thought it sounded like someone had a graphic eq and changed the settings, but after a while no problem I got used to it and I like the Russian tube, all the frequencies are still there top and bottom, its just a slight different sound. The 6P1 just more mellow, but no details missing from the Russian tube. The missus loves the Russian tube now, and maybe we didn't give it enough time to run in. As far as she is concerned the Russian tubes stay in for now. My favourite is the Beijing. I swapped tubes for 4 songs 3 times tonite. They are that close. Thanks Jonas cause I had given up on them. Seems the eq is different around say 600Hz and 1.5kHz just guessing. Also depends on what music type you are listening to. Missus loves the scarecrow by Pink Floyd on the 6P1P but I know its nicer on the 6P1, but then "a great day for freedom" by Pink Floyd comes on, OK I give up. Thanks Jonas. Nothing wrong with 6P1P-EV. Because I was a semi-pro musician and sang for many years, I listen for real sounds and when I hear it in my home my heart sings along. Now I am listening to "comfortably numb" and its just real nice and real. Thats why I started this thread, just a thumbs up to a nice cheap amp, but needs work to get it set up and then its fine. No fancy components. Had mine 2 years. Still my favourite of all my amps and never modified, just fixed :)
 
Ian.

Offline assendor

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #12 on: April 03, 2009, 03:47:15 AM »
Hello Ian,

Most important thing is that we like what we have.
It is no use to me, or you, that someone else tells us what is right.

Guidelines to how to get what we want is something different, still we can have different taste to what is right.

If you earlier on have experience in singing and music production, of course what you like and feel gives you the "correct" experience still is the most correct thing for you.

Still I think the Russian tube there can benefit from higher bias currents, I'll do some experiments myself with this tube later on.
Now there are so many things I'm suppose to test and do and the spring is closing in, forcing me to use more time outside in my garden and get my 28m2 greenhouse going.

It is really pleasant you do find this small and cute amp so well sounding.
At that low cost, and you have had it for two years it really is a bargain.

If you sometime in the future find someone that has, or you find it interesting to buy it yourself,
you should let Charlize2 get a chance.
Now it has to be said, she is most likely far more "raw sounding" than most your tube amp is.
If you prefer the Chinese Tubes there over the 6N1P, there might be a slight chance you will find Charlize2 also different.
I am a little afraid of telling others what to buy, since they might in some cases have totally different taste and equipment as well,, so it might not sound anywhere close to what they "like". :)

It is really hard to say what sounds the best without having a system for some time.
The immediate impression is somehow very different from the impression you get when listening to it over a longer period of time.

It should be interesting to do some mods to some of your other amps then??? Maybe?
What where the others you had, rather cheap ones, that you can play with, and not feel the world is crushing if you do something that could cause more damage than planned?

You have done quite a few things already I can see...
It interests me that you find that little Push and Pull amp sounding so well....
Wonder what it is with it that is so to like..... If it wasn't for the extreme shipping cost, it would be fun to try it..

You do not find the EL84 to sound very well?
Do you have correct impedance on your transformer, I don't think the 6L6GC normally uses same impedance as the EL84 tubes on output transformers?

Chinese 6L6GC equivalent, but when that amp (Ming Da).
What amp is it?

-Jonas

Offline ian444

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #13 on: April 04, 2009, 07:28:59 PM »
Hi Jonas,

The EL84 will not plug straight in to the Mengyue as it has a different pinout, also it needs 50% more heater current. I have never heard an EL84 pp amp but have only read good things about that tube. I do have some Russian EL84 sitting around here waiting...

Link to Mingda: http://www.coemaudio.com.au/Amplifiers/Integrated-Amplifiers/122/

It is has been modified, but I have not tried any new changes since January.

The other amp is a Chinese SE with EL34 (originally KT88), and although it sounds OK now, I would like to try this schematic on it one day: http://basenjes.de/tubes/jbsel34.htm  Pin 1 on the EL34 is tied to the output transformer which is interesting.

Ian.

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Re: Mengyue/Music Angel Mini tube amp 6P1 pp
« Reply #14 on: April 04, 2009, 07:49:02 PM »
Hello Ian,

Interesting, interesting... Yes it is fun playing with tubes.

I must have misunderstood what you wrote then:
"I have had no problem with the Chinese 6L6GC equivalent, but when that amp (Ming Da) started blowing up tubes I eventually fixed it by doing a SimpleEL84 diyparadise conversion"

It is probably no good idea to stuff that amp of yours with the EL84, since 50% heater current and maybe other demands is not suitable for your existing power supplies.

You have Music Angel KT88 Push pull amp? And the Ming Da?
Sorry that I don't quite understand always.

That EL34 SE amp there looks interesting.. Perfectly interesting.
DO you have any idea what bias current those EL34 tube is running at in this circuit?
IF you have not tried SE amp yet, you should.. IT is different.
bias current 70mA? maybe??

-Jonas