Hello,
one short update:
Bild: gorgtech_neuhuyj.jpg - abload.de
12AX7 + 2x E80CF ( pentode connected as triode, triode used as a phase splitter) + EH EL34 ( connected as triode ).
The circuit works fine, I´ll have to measure the frequency response and add a few minor changes to my schematic.
George
one short update:
Bild: gorgtech_neuhuyj.jpg - abload.de
12AX7 + 2x E80CF ( pentode connected as triode, triode used as a phase splitter) + EH EL34 ( connected as triode ).
The circuit works fine, I´ll have to measure the frequency response and add a few minor changes to my schematic.
George
So you are using the stock Meng output and PSU transformers with EL34 in PP? Did you work out what the primary impedance of the OPTs is?
The PSU must limit the power of the EL34s.
Would love to see a schematic, particularly the pentode phase splitter. I'm sure that the phase splitter we have now is probably a limiting factor if run on the 250v B+
I might have to try something like this if it sounds good.
Gary
Last edited:
Yep, unless Gary has made some changes, but that's what I'm using, plus the mosfet followers.
Gary, I think Meng also made a dedicated EL34 amp, so it probably has different trannies and higher B+.
Starne, I have done my best to explain the risks, I would try it on the amp if it was mine, but I cannot be responsible if it goes tits up. Hopefully it will be fine just as stock.
Hello,
the measured OPT impedance is ca. 8K raa.
Here a few more pictures:
http://www.abload.de/img/gorg_1ojo9.jpg
http://www.abload.de/img/gorg_2vvw2.jpg
http://www.abload.de/img/gorg_3wwqb.jpg
Best regards,
George
the measured OPT impedance is ca. 8K raa.
Here a few more pictures:
http://www.abload.de/img/gorg_1ojo9.jpg
http://www.abload.de/img/gorg_2vvw2.jpg
http://www.abload.de/img/gorg_3wwqb.jpg
Best regards,
George
No I haven't done any more on the Meng at all, just using it on the Dec 26 circuit with a couple of minor changes.
I didn't realise that George had started with a EL34 Meng, I assumed it was the 6P1 he was trying to convert into EL34.
Gary
I also rebuilt my Mengyue Mini to a better circuit, but I kept the same tube compliment and the same transformers. Still, it halved the distortion to about 0.2% at 1W and noise from -82dB to -91dB
(low frequency stability and distortion in the original was really bad, over 1% at 100Hz at 1W)
Now I use the amp all the time!
http://www.audioxpress.com/magsdirx/ax/addenda/media/blencowe2996.pdf
(low frequency stability and distortion in the original was really bad, over 1% at 100Hz at 1W)
Now I use the amp all the time!
http://www.audioxpress.com/magsdirx/ax/addenda/media/blencowe2996.pdf
Merlin, your amp came with EL84 valves originally, did it not? Were they actual EL84s or the 6P14P/6P15 versions? There seems to be so many variations of these amps that I think they build them as the orders come in....
Anyway my 6P1 version is running nicely as well, after the safety/overvoltage/ugly_preamp issues were addressed. I am still using the PCB albeit rearranged. The only issue I have with it is the lack of power with my inefficient speakers. I knew that going in, though.
I am also building up a duplicate of my 6P1 Meng, on a (larger) home-made chassis, with some old UL output transformers that came from a local EL84 stereo amp. I'll see how that sounds and if I find a preamp/driver stage that show significant improvement over what I have, I'll look at incorporating it into the Meng. I have a good supply of 6N1/2/3P-EV and 6P1P-EV valves, so plenty of possibilities.
I could even turn it into Franken-Meng with 7C5s (loctal 6V6GT), as I have a few of those lurking about.
Gary
Anyway my 6P1 version is running nicely as well, after the safety/overvoltage/ugly_preamp issues were addressed. I am still using the PCB albeit rearranged. The only issue I have with it is the lack of power with my inefficient speakers. I knew that going in, though.
I am also building up a duplicate of my 6P1 Meng, on a (larger) home-made chassis, with some old UL output transformers that came from a local EL84 stereo amp. I'll see how that sounds and if I find a preamp/driver stage that show significant improvement over what I have, I'll look at incorporating it into the Meng. I have a good supply of 6N1/2/3P-EV and 6P1P-EV valves, so plenty of possibilities.
I could even turn it into Franken-Meng with 7C5s (loctal 6V6GT), as I have a few of those lurking about.
Gary
It came with 6P14s, which I am still using. (I use a lot of these in general, and they seem just as good as EL84s)
Excellent article Merlin, thanks for the link! It's interesting that such a cheap amp can be made to sound respectable with some major cct changes. Not sure if you realize that Gary and I (and maybe/soon Tvr) are using a similar cathodyne cct, except we are driving 6P1 output tubes. Lots of great ideas in your article, thanks very much again, because really, I have no idea what I'm doing, just following my ears. We have spent considerable amounts of time on your valvewizard website trying to get up to speed and it has been extremely helpful to say the least (well for me anyway, maybe best just to speak for myself). I am wondering if you intend to get around to writing up push-pull power calculations on your PP page, you sort of hinted at that in the 5th paragraph, or maybe you are saving that for your next book...
Ian.
Ian.
Oops you're right, I never did get round to that! It's very easy- I have added it to the bottom of the page.
Thanks, Ian. And thanks for the link to the paraphrase description, "The Valve Wizard." I'll do just that!
"David, I would listen to the Meng X1 stock for a week, let it break in a bit, get familiar with its sound, then try the Russian 6N2P-EV. There is a problem here though, which I didn't mention before, and just realized now. The Meng (yours and ours) uses a paraphase phase splitter which has a trimpot for each channel, to balance the signal amplitudes to each half of each channel. Putting a new/different tube in there may upset the original balance (if it was ever balanced in the first place). So unless you are comfortable with measuring the grid voltages to the output tubes with a sine wave on the inputs your results may not be ideal. You can't really do any damage if the amp is not adjusted, it may or may not sound right is all that will happen. If it doesn't sound right put the Chinese tubes back in their original sockets. Some reading on the paraphase here. I can't see any reason to try 6N1P-EV unless your curiosity outweighs a small purchase price. OK I admit it, I would try it if the tubes cost less than $5 each but keep in mind what I said about the paraphase splitter.
I didn't find the Russian 6P1P-EV to be any better than the Chinese 6P1, the wife liked the Russian tubes as they were a bit brighter, but I liked the Chinese ones as they were more mellow/warm. But that was just going on the tubes we had at the time, with a stock amplifier, YMMV. I did have some funny stuff going on with the Chinese tubes regarding grid voltages, and so did Tvr if I remember right, but the Russian ones have been very stable and do everything right. So if you want to buy some Russian 6P1P-EV as backup, that would be a good idea IMO, as in, it certainly wouldn't hurt.
Ian"
"David, I would listen to the Meng X1 stock for a week, let it break in a bit, get familiar with its sound, then try the Russian 6N2P-EV. There is a problem here though, which I didn't mention before, and just realized now. The Meng (yours and ours) uses a paraphase phase splitter which has a trimpot for each channel, to balance the signal amplitudes to each half of each channel. Putting a new/different tube in there may upset the original balance (if it was ever balanced in the first place). So unless you are comfortable with measuring the grid voltages to the output tubes with a sine wave on the inputs your results may not be ideal. You can't really do any damage if the amp is not adjusted, it may or may not sound right is all that will happen. If it doesn't sound right put the Chinese tubes back in their original sockets. Some reading on the paraphase here. I can't see any reason to try 6N1P-EV unless your curiosity outweighs a small purchase price. OK I admit it, I would try it if the tubes cost less than $5 each
but keep in mind what I said about the paraphase splitter.I didn't find the Russian 6P1P-EV to be any better than the Chinese 6P1, the wife liked the Russian tubes as they were a bit brighter, but I liked the Chinese ones as they were more mellow/warm. But that was just going on the tubes we had at the time, with a stock amplifier, YMMV. I did have some funny stuff going on with the Chinese tubes regarding grid voltages, and so did Tvr if I remember right, but the Russian ones have been very stable and do everything right. So if you want to buy some Russian 6P1P-EV as backup, that would be a good idea IMO, as in, it certainly wouldn't hurt.
Ian"
Well, I figured out what caused the failure in the transformer that Daniel sent me.
I tried powering it up since I could not find a short when I Ohm'd it.
When I flipped the circuit breaker on the B+ it went BVvvvttttttt! and popped the breaker.
The fault was all the way at the bottom of the stack, closest to the bobbin.
Don't ya know it would require unwinding the entire transformer to find it!
I'll try to get some pictures cleaned up to post in the next couple of days, as it is late tonight I'll just state the primary shorted to the secondary.
The transformer is wound with one layer of secondary, 10 layers of primary, ct, 10 layers of primary, one layer of secondary.
Two layers of 0.002" craft paper is used to separate the winding layers. There is no margin tape used to force spacing at the outside of the bobbin. This allowed the secondary to slip by the craft paper and short out to the primary.
Funny thing is that the other transformer measured an open on the secondary. I soldered the connection between the two secondary windings and it fixed the problem. The transformer plays reasonably well, but after dissecting one I don't trust them.
There needs to be a bit more care in winding them. Use margin tape to set the edge boundary spacing. Mylar between the primary and secondary layers, etc.
I'm tempted to use the E-I cores and bobbins to make an attempt at winding a set myself. I'm sure I can do a better job, but it will be time consuming so it will probably set on the back shelf forever.
I tried powering it up since I could not find a short when I Ohm'd it.
When I flipped the circuit breaker on the B+ it went BVvvvttttttt! and popped the breaker.
The fault was all the way at the bottom of the stack, closest to the bobbin.
Don't ya know it would require unwinding the entire transformer to find it!
I'll try to get some pictures cleaned up to post in the next couple of days, as it is late tonight I'll just state the primary shorted to the secondary.
The transformer is wound with one layer of secondary, 10 layers of primary, ct, 10 layers of primary, one layer of secondary.
Two layers of 0.002" craft paper is used to separate the winding layers. There is no margin tape used to force spacing at the outside of the bobbin. This allowed the secondary to slip by the craft paper and short out to the primary.
Funny thing is that the other transformer measured an open on the secondary. I soldered the connection between the two secondary windings and it fixed the problem. The transformer plays reasonably well, but after dissecting one I don't trust them.
There needs to be a bit more care in winding them. Use margin tape to set the edge boundary spacing. Mylar between the primary and secondary layers, etc.
I'm tempted to use the E-I cores and bobbins to make an attempt at winding a set myself. I'm sure I can do a better job, but it will be time consuming so it will probably set on the back shelf forever.
Thanks for the report. Always good to know any extra info, whatever it is.
Regarding the 6W output I was getting (and low output reported by others), it still doesn't make sense to me. Surely the new phase splitter implant is simply not delivering the required voltage swing to drive the output tubes, as no matter what method of calculating power, or whichever data sheet I use for the loadlines, it still doesn't add up. Something to look into again one day.
Ian.
Regarding the 6W output I was getting (and low output reported by others), it still doesn't make sense to me. Surely the new phase splitter implant is simply not delivering the required voltage swing to drive the output tubes, as no matter what method of calculating power, or whichever data sheet I use for the loadlines, it still doesn't add up. Something to look into again one day.
Ian.
I would be interested to know what values of 6P1 grid resistor and grid coupling capacitor you guys are using. Perhaps the load is too heavy for the phase splitter?
There is some discussion on the Suppo thread about raising the grid resistor value and dropping the coupling cap value.
I haven't measured to see what runs out of steam first, but I think TVR said that the splitter was first to clip.
I'm still using the original cap and 220k resistor that Ian had in his first cathodyne. Maybe raising the 220k to closer to 1M may up the drive. How that impacts with a source follower I am unsure as I don't have one in mine yet.
Regarding differences in OPTs, it will be an interesting comparison to the Hammonds. We were bemoaning the differences in dc resistance of the windings between units, well I have just got hold of a pair of old Pye EL84 UL OPTs and they exhibit the same differences that the stock Meng ones do, so the problem isn't limited to the Chinese iron. However, the Pye ones are likely 50 years old.....
I am building a PP amp with those OPTs at the moment. It will be ECL86 based to start, but assuming the iron is actually OK I might do a rewire with the Meng tubes for comparison later. I may have difficulty getting the B+ down to Meng levels though, as this one has very beefy power iron and is tube rectified. No load B+ was 415v
Gary
There is some discussion on the Suppo thread about raising the grid resistor value and dropping the coupling cap value.
I haven't measured to see what runs out of steam first, but I think TVR said that the splitter was first to clip.
I'm still using the original cap and 220k resistor that Ian had in his first cathodyne. Maybe raising the 220k to closer to 1M may up the drive. How that impacts with a source follower I am unsure as I don't have one in mine yet.
Regarding differences in OPTs, it will be an interesting comparison to the Hammonds. We were bemoaning the differences in dc resistance of the windings between units, well I have just got hold of a pair of old Pye EL84 UL OPTs and they exhibit the same differences that the stock Meng ones do, so the problem isn't limited to the Chinese iron. However, the Pye ones are likely 50 years old.....
I am building a PP amp with those OPTs at the moment. It will be ECL86 based to start, but assuming the iron is actually OK I might do a rewire with the Meng tubes for comparison later. I may have difficulty getting the B+ down to Meng levels though, as this one has very beefy power iron and is tube rectified. No load B+ was 415v
Gary
Meng Yue Mini Transformer dissection
Electrical Parameters:
Primary Inductance Lp – 5.4H
Primary Leakage Inductance Ls – 7.7mH
Primary Resistance Rp – 56 Ohm/62 Ohm
Secondary resistance Rs – 0.256 Ohm
Observations:
No enamel/varnish holding stack together. It will probably buzz.
Stack-Up:
Outer covering 2 layers of craft paper 0.002” Thick. (0.002” to 0.0025” depending on compression with calipers). The winding termination are sandwiched here, followed by two more layers of craft paper.
Outer layer is a single layer consisting of 20 turns of 0.028” Dia magnet wire.
Two layers of craft paper.
The secondary consists of 10 layers 0.010” dia magnet wire alternated with two layers of craft paper..
Winding counts are 62, 60, 56, 58, 61, 60, 60, 59, 60, 59. These were probably meant to be 60T per layer, and I may have miss counted so don’t take these counts to heart.
The center tap is brought out after 10 layers, then another 10 layers of windings.
Winding layer counts are 64, 62, 61, 60, 61, 60, 63, 62, 64, 60.
There is a solder joint between segments of wire on layer 6 where the spool apparently ran out. No insulation painted over the solder joint. This is a weakness as it decreases insulation strength.
Finally two more layers of craft paper and the other secondary winding layer consisting of 20T 0.028” magnet wire.
Two more layers of craft paper are wrapped around the bobbin.
It is between the secondary and first primary layers that I found the short that caused problems in this transformer. The craft paper kinked in the corner allowing the primary winding on the edge to pull against the secondary winding. Insufficient insulation allowed the two to short together under application of B+=250VDC + AC=250?, probably over 500V potential difference between the two wires at this point during clipping excursions of the output at the final tube driving the transformer.
Here is the short in the corner of the transformer:
Electrical Parameters:
Primary Inductance Lp – 5.4H
Primary Leakage Inductance Ls – 7.7mH
Primary Resistance Rp – 56 Ohm/62 Ohm
Secondary resistance Rs – 0.256 Ohm
Observations:
No enamel/varnish holding stack together. It will probably buzz.
Stack-Up:
Outer covering 2 layers of craft paper 0.002” Thick. (0.002” to 0.0025” depending on compression with calipers). The winding termination are sandwiched here, followed by two more layers of craft paper.
Outer layer is a single layer consisting of 20 turns of 0.028” Dia magnet wire.
Two layers of craft paper.
The secondary consists of 10 layers 0.010” dia magnet wire alternated with two layers of craft paper..
Winding counts are 62, 60, 56, 58, 61, 60, 60, 59, 60, 59. These were probably meant to be 60T per layer, and I may have miss counted so don’t take these counts to heart.
The center tap is brought out after 10 layers, then another 10 layers of windings.
Winding layer counts are 64, 62, 61, 60, 61, 60, 63, 62, 64, 60.
There is a solder joint between segments of wire on layer 6 where the spool apparently ran out. No insulation painted over the solder joint. This is a weakness as it decreases insulation strength.
Finally two more layers of craft paper and the other secondary winding layer consisting of 20T 0.028” magnet wire.
Two more layers of craft paper are wrapped around the bobbin.
It is between the secondary and first primary layers that I found the short that caused problems in this transformer. The craft paper kinked in the corner allowing the primary winding on the edge to pull against the secondary winding. Insufficient insulation allowed the two to short together under application of B+=250VDC + AC=250?, probably over 500V potential difference between the two wires at this point during clipping excursions of the output at the final tube driving the transformer.
Here is the short in the corner of the transformer:
An externally hosted image should be here but it was not working when we last tested it.
I just finished testing four transformers including the Meng Yue Mini.
I got the same output with it as the others (within a tenth of a watt or so).
I'm running a .022uF coupling cap and 680K grid to ground resistor with no grid stop. Cathodyne with 68K top and bottom.
I've got frequency sweeps of the Meng Yue transformer, Hammond 1608, 1609, and a Olson transformer for comparison. I've got it all in a 228KB word document. Is there any way to upload it?
I got the same output with it as the others (within a tenth of a watt or so).
I'm running a .022uF coupling cap and 680K grid to ground resistor with no grid stop. Cathodyne with 68K top and bottom.
I've got frequency sweeps of the Meng Yue transformer, Hammond 1608, 1609, and a Olson transformer for comparison. I've got it all in a 228KB word document. Is there any way to upload it?
I too would be interested to hear a report from Daniel on the Hammonds, its been over 2 weeks since he fitted them!
Gary I'm using 0.1uF into approx 400K. Current schem is here. The only specs I see mentioned for the grid resistor for the 6P1P are 500K. Not sure Steve how you are getting away with 680K, been meaning to ask, but obviously it works.
As far as gain from the preamp stage goes, I might try a cap across the cathode resistor of the 6N1 and see what that does, one day. I remember you had one in there at some early stage Gary.
For the document you want to post, you might have to zip it up.
Ian.
Gary I'm using 0.1uF into approx 400K. Current schem is here. The only specs I see mentioned for the grid resistor for the 6P1P are 500K. Not sure Steve how you are getting away with 680K, been meaning to ask, but obviously it works.
As far as gain from the preamp stage goes, I might try a cap across the cathode resistor of the 6N1 and see what that does, one day. I remember you had one in there at some early stage Gary.
For the document you want to post, you might have to zip it up.
Ian.
Sorry guys, I didn't had time to do side to side comparison between the two Meng yet. I had a couple of pair of speakers to finish. And it will probably not be this weekend because I will not be home. But from my hearing memory I can tell that there's at least a slight improvement in the sound. Basses seem to get a little deeper and the highs are more present.
Steven, you want me to compare the output on the same volume position on the knob or you want to know if I get an higher voltage output overall?
Daniel
Steven, you want me to compare the output on the same volume position on the knob or you want to know if I get an higher voltage output overall?
Daniel
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