Ian, for all the changes you have made it still looks pretty neat.
I believe you are correct on the screen. It's purpose is to screen the anode to reduce the effect of changes in plate voltage inducing changes in plate current. As such it will allow you to adjust the tube bias in place of varying the grid voltage.
I don't think it will make a significant change in the sound of the system, other than reducing feedback from the plate supply effecting the operation since you are now regulating the screen supply. This should be minor.
On swapping 6N1P and 6N2P tubes, I found that I had to change the bias point when I swapped them to get each to sound best. Once I changed the bias resistor, I had to change the anode resistor to get the gain back when going from 6N2P to 6N1P.
I believe you are correct on the screen. It's purpose is to screen the anode to reduce the effect of changes in plate voltage inducing changes in plate current. As such it will allow you to adjust the tube bias in place of varying the grid voltage.
I don't think it will make a significant change in the sound of the system, other than reducing feedback from the plate supply effecting the operation since you are now regulating the screen supply. This should be minor.
On swapping 6N1P and 6N2P tubes, I found that I had to change the bias point when I swapped them to get each to sound best. Once I changed the bias resistor, I had to change the anode resistor to get the gain back when going from 6N2P to 6N1P.
Hello.
I just finished finally wiring the gnfb wires on my Mini 6P1. After a couple of tries and feedback...I get the wires connected the right way. As seen on this picture:
the gnfb wires are connected this order originally: Brown-Red & White-Black but with new transfos it's now Brown-Red & Black-White.
I'll do some listening and comparisons during the week and I'll let you know if it's changed and improved sonically.
Daniel
I just finished finally wiring the gnfb wires on my Mini 6P1. After a couple of tries and feedback...I get the wires connected the right way. As seen on this picture:
the gnfb wires are connected this order originally: Brown-Red & White-Black but with new transfos it's now Brown-Red & Black-White.
I'll do some listening and comparisons during the week and I'll let you know if it's changed and improved sonically.
Daniel
1) Yes, the -EV briefly means better build quality and tighter QA. Do a search for the full details.
2) Swap a 6N2 for 6N1? Technically yes, but who knows if it will sound better. It will draw more heater current also, which is a risk of unknown size, but the little Mengyue amps seem to handle it so the X1 should be lesser risk. A better bet if you have to try different tubes would be 6N2P-EV as I have found the Chinese 6N2's and 6N1's to vary a lot between each triode section, and the Russian 6N1P-EV's to be consistent, I have not bought any 6N2P-EV but would expect similar quality/characteristics. The Russian 6P1P-EV's I have bought also are consistent. I have also found a couple of Chinese 6P1's to have leakage between the grid and cathode, but that is also just my experience with a handful of tubes. There was an old Beijing factory pre 1986 I think and then that got disassembled and since then its been the Shuguang factory with a different logo, well 2 logos. The later one is the bird symbol. A lot of the small Chinese amps on ebay use the Beijing NOS tubes. The logo on these is a small star with 3 stripes each side like a Svetlana winged C, and its usually printed along the length of the valve (sideways). I did look right into the Chinese tube history at one stage but now I just get Russian, they're a lot cheaper and work as expected. I have not had a problem with the actual sound of the Chinese 6P1's though, so if they are working fine I would leave them in. Gary and I are using 6N1's since we changed the schematic as far as I can recall, but for a standard Meng, I don't know if anyone has tried 6N1 in it. Certainly would not hurt to try, might sound better, might sound worse.
From looking at the PCB pics of the Meng X1 on ebay, it appears to have the same schem as the Mengyue 6P1 except for the doubled up output tubes. The power supply is a bit different with the choke in it which is proly a good thing. Be good to hear a report on it, how it sounds.
LED's sure don't seem to behave like a constant voltage source. Just got around to sorting the batch of 200 cheap LED's. I was looking at them between 15 and 35 mA.
They ranged from about 2 to 2.4V drop. 20% variation is not what I call constant voltage.
At 24mA, the selection of 200 ranged between 2.10 and 2.16V, pretty close to a standard deviation around 2.13. Now I am burning in a string to see if they change over 24 hours.
They ranged from about 2 to 2.4V drop. 20% variation is not what I call constant voltage.
At 24mA, the selection of 200 ranged between 2.10 and 2.16V, pretty close to a standard deviation around 2.13. Now I am burning in a string to see if they change over 24 hours.
Hello,
without any words..
Pic is too small to see clearly, but is that point-point rewiring?
Gary
Hello,
yes, I´m rewireing the amplifier.
Bild: heater-connection003yokz.jpg - abload.de
I had to mod. the transformer in order to obtain a stable 12,6V AC heater winding ( both 6,3V windings dropped the voltage below 5,4V AC ).
I can post the schematic of the new amplifier too.
George
yes, I´m rewireing the amplifier.
Bild: heater-connection003yokz.jpg - abload.de
I had to mod. the transformer in order to obtain a stable 12,6V AC heater winding ( both 6,3V windings dropped the voltage below 5,4V AC ).
I can post the schematic of the new amplifier too.
George
A string of LED's dropping 14.00 volts and 22mA, 48 hours and still dead on 14.00V.
So, no drift, just sure not 1.6V. I wonder if these 5 cent wonders have a resistor in them? That would explain their higher than expected drop and their less than constant voltage operation. I will compare some older LED's I have.
So, no drift, just sure not 1.6V. I wonder if these 5 cent wonders have a resistor in them? That would explain their higher than expected drop and their less than constant voltage operation. I will compare some older LED's I have.
It would be typical to have a fairly large voltage drop variation in LEDs. They are indicator bulbs after all, so I wouldn't expect accuracy or consistency in items made for the consumer appliance market.
No, they won't have a resistor in them. You'll just have to hand pick them for the task.
Gary
No, they won't have a resistor in them. You'll just have to hand pick them for the task.
Gary
There are a couple different structure/dopant red LEDs. I don't know if the old cheap 1.6V ones are still made or not. The advantage with them is supposed to be lower dynamic resistance.
You will get a good bit of variance in voltage from unit to unit. However once nder constant bias, each one should hold it's voltage drop with good stability.
You will get a good bit of variance in voltage from unit to unit. However once nder constant bias, each one should hold it's voltage drop with good stability.
Hi George,
The extra 3 windings around the transformer, how much do they raise the voltage of that heater winding? I guess you need special wire, where do you get that? Or will just normal solid copper wire be OK? Is that a 555 on the PCB, to delay the B+?
Tvr, the voltages depend a lot on the material used to make them. 2V at 22mA is pretty normal in my book, 1.8V @ 15mA is difficult to find these days.
Edit - sorry missed your post Gimp. Yes, what Gimp said!
The extra 3 windings around the transformer, how much do they raise the voltage of that heater winding? I guess you need special wire, where do you get that? Or will just normal solid copper wire be OK? Is that a 555 on the PCB, to delay the B+?
Tvr, the voltages depend a lot on the material used to make them. 2V at 22mA is pretty normal in my book, 1.8V @ 15mA is difficult to find these days.
Edit - sorry missed your post Gimp. Yes, what Gimp said!
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Hello Ian,
I´ve built a additional circuit board for the dc heater (input tubes) and the NE555 delay circuit for the anode voltage. I can post the circuit too although I guess it is not hard to figure out.
Unfortunately I have to use a voltage doubler and stick with the original chinese power supply in order to obtain 400Vdc.
I´ve connected the mod. 6,3V winding in series and used some spare enameled copper wire and have a stable 12,6V winding ( EL34 connected in series, parallel. I use the 12,6V winding for the additional circuit board too ).
I´d like to use ECF80 / PCF80 tubes as a phase splitter ( I have many spare valves ) .
Best regards,
George
I´ve built a additional circuit board for the dc heater (input tubes) and the NE555 delay circuit for the anode voltage. I can post the circuit too although I guess it is not hard to figure out.
Unfortunately I have to use a voltage doubler and stick with the original chinese power supply in order to obtain 400Vdc.
I´ve connected the mod. 6,3V winding in series and used some spare enameled copper wire and have a stable 12,6V winding ( EL34 connected in series, parallel. I use the 12,6V winding for the additional circuit board too ).
I´d like to use ECF80 / PCF80 tubes as a phase splitter ( I have many spare valves ) .
Best regards,
George
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Meng X1 6P1--tube strategy
Thanks Ian,
So...I have a Meng X1 6P1 on the way.
As it stands now in your experimentation,
what tubes should I plan on substituting, if any?
Mine is supposed to come with 2 x 6N2,
so I thought I might try substituting Russian 6N2P's.
And regarding the 8 x 6AQ5's/6P1's:
I can try substituting the Russian 6P1-EV's,
but Gary (and you?) say this hasn't improved anything.
Right?
--David
Thanks Ian,
So...I have a Meng X1 6P1 on the way.
As it stands now in your experimentation,
what tubes should I plan on substituting, if any?
Mine is supposed to come with 2 x 6N2,
so I thought I might try substituting Russian 6N2P's.
And regarding the 8 x 6AQ5's/6P1's:
I can try substituting the Russian 6P1-EV's,
but Gary (and you?) say this hasn't improved anything.
Right?
--David
That is the idea, but if I had a constant bias, then I would not need an LED, a resistor would be fine. I tested a bunch of odd ones I have. All react about the same. The point is they do not maintain constant voltage with varying current. About 10 times better than a resistor, but not constant.
Anyway, now to build up some strings reasonably well matched for the Meng. It should help make the gain more linear. Still a good idea, but nothing like fixed bias.
Had a thought looking at the board. Would the ripple decrease if I cut the heater traces off the board and used nicely dressed twisted pairs instead of the lands? After all, I have to hack up the board to change the input design anyway.
Handy chart. Never seen that before. I would bet everything is "high efficiency" now. Slope is about right.
You don't need to hack the PCB for the input stage mods as per the earlier schematics with the 6N1P. I managed to get all my changes done without cutting any traces.
Tvr, with the LED's, I agree they do not appear to be a constant voltage source (or is that a sink?) But better than a resistor as you say. I found 500mV rms on the cathodes at clipping with LED arrays. Something with a better dynamic impedance than an LED would be a straight piece of wire and use fixed bias. Seriously though, I found the LED's to sound very good. I have not compared it to fixed bias yet.
George from Tubelab tried some LED's in his Simple PP amp prototype, worth reading. Read more here. Interesting that George found less distortion with individual LED arrays, vs a combined array for each output pair.
Update on my amp, I put the bias back up to 40mA, slight improvement, but after a week of screen grid regulators in place I knew the bass had suffered a bit. Tonight I put all the screen voltages to max (240V, well, 230V from screen to cathode) and adjusted the grid voltage for 40mA. Still didn't sound like I remembered, so the screen grid regulators got removed and the sound was back to like it used to be, more musical, more dynamics, good bass. Funny how I can spend 2 days doing a mod that "should" make it sound better, then when I listen, even if its worse I think there is no change...but after a week I wake up to it. I have only 2 more things to try, UL and triode mode. Maybe I try triode tomorrow. Make that 3, one day I need to try some GFB, I'm pretty sure I have 6dB to spare at least, worried about losing something though.
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
and use fixed bias. Seriously though, I found the LED's to sound very good. I have not compared it to fixed bias yet.George from Tubelab tried some LED's in his Simple PP amp prototype, worth reading. Read more here. Interesting that George found less distortion with individual LED arrays, vs a combined array for each output pair.
Update on my amp, I put the bias back up to 40mA, slight improvement, but after a week of screen grid regulators in place I knew the bass had suffered a bit. Tonight I put all the screen voltages to max (240V, well, 230V from screen to cathode) and adjusted the grid voltage for 40mA. Still didn't sound like I remembered, so the screen grid regulators got removed and the sound was back to like it used to be, more musical, more dynamics, good bass. Funny how I can spend 2 days doing a mod that "should" make it sound better, then when I listen, even if its worse I think there is no change...but after a week I wake up to it. I have only 2 more things to try, UL and triode mode. Maybe I try triode tomorrow. Make that 3, one day I need to try some GFB, I'm pretty sure I have 6dB to spare at least, worried about losing something though.
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
Ian,
Thanks! So, just to make sure: I can try all those different tube swaps (pre: 6N2P-EV and 6N1P-EV; power: 6P1P-EV) without blowing up the amp? The swaps might make it sound better, or might not. Right?
"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"
Thanks! So, just to make sure: I can try all those different tube swaps (pre: 6N2P-EV and 6N1P-EV; power: 6P1P-EV) without blowing up the amp? The swaps might make it sound better, or might not. Right?
"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"
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