Tubes for Yaqin MC-10L Amp

[Jim]

I posted a question on my amp that I just picked up, and being that we now have a section just for this, I had a few questions on tubes and biasing them.

 

I purchased this amp about a month ago used and wanted to see what tubes would be recommended, and what "snake oil" is out there for upgraded tubes with NOS vs today's versions.

 

The amp uses EL34B or 6CA7 as well as 6N1 and 6H1N tubes. I just replaced the Chines tubes with Russian 6H1N and Tung Sol EL34B (new versions).

 

My question was what other tubes would be good to use and if I should not waste my time trying out different tube types (ECC88, 6922,6N23P,) and if Sylvania, Amperex, and Siemens really make a difference.

 

I am also curious on biasing and how to do it properly. And what biasing tool would be recommended.

 

Below is the original question I posted, being we have this now, I figured it can go here.

 

Posted 20 July 2015 - 10:38 PM

I have another post on KG speakers but am looking for recommendations on tube replacement for my Yaqin Amp. It uses 6H1N or 6N1 tubes and I've read others are using ECC88, 6922, 6DJ8, 6N23P tubes.

 

I purchased NOS 6N1P-VI Gold Pin and grid NEVZ Novosibirsk Russian tubes (May 1990) for the amp and I'm not sure they are broken in yet as there are about 100 hours or so on them. The SQ seems to be just OK, nothing great, so again I don't know if it will open more after more hours on these tubes. I don't know if these are generic tubes or not either.

 

I'm also looking at Amperex 6922 Green label 1968 NOS tubes, Siemens E88CC Grey Shield NOS, Reflektor 1974 6N23P, and Sylvania Gold Brand Gold Pin 6922 also NOS. I am not savvy on tubes so I'm looking for recommendations. I'm looking for a nice open crisp mid and high with a wide soundstage. I'm also using the new Tung Sol Platinum EL34B.

Edited July 29, 2015 by Jim

[tube fanatic]

Jim, to set the bias you will need a multimeter.  lt doesn't have to be anything fancy.  On top of the amp, adjacent to each output tube there should be (assuming this isn't one of the old models) a pair of jacks into which you will insert the meter probes.  If I recall, the bias pots are little, board mounted, plastic affairs which require a hex shaped, plastic alignment tool to be adjusted (probably a similar type to what we use for radio/tv servicing).  Did yours come with one by chance?  If not, you could pick up something like this:  http://www.landmelectronics.com/product.cfm/28653/

 

The adjustment process is fairly simple:  let the amp warm up for about 15-20 minutes (it doesn't matter if you play music or not while doing this).  Then, turn the volume control down all the way, and turn off whatever source you were listening to (or switch the input selector to an unused position).  Set your meter to it's lowest DC range (unless it is autoranging in which case you don't have to do anything).  What we are looking for is 0.35 to 0.4 volts at each tube.  The adjustment is going to be fairly sensitive- a slight turn can change the reading quite a bit.  Don't get obsessive about setting each tube to be exactly the same!  Once each tube is set within the proper range, you are done.

 

Post with any other questions you have about the process.  As to tube types, I'll pick up on that later when I'm back on the computer!

 

Maynard

 

 

[Jim]

Maynard,

 

It didn't come with the tool, so I will have to purchase one. I am attaching a photo of it. Your memory is pretty good.

 

So I am assuming that I won't have to get the multimeter with the socket then.  The prongs going in to the left or right will act as the socket. And I will just have to adjust. Is that correct?

Edited July 29, 2015 by Jim

[tube fanatic]

Jim, it looks like they have provided a pair of test points for each output tube along the outside edge of the chassis.  So, you need to insert the probes of your meter into those.  They should be what we call pin jacks which will grip the meter probes with reasonable firmness.  Then, you would adjust the bias set control of each tube with the hex tool.  Of course, you need to move the meter probes to the jacks adjacent to each tube before adjusting its control.  Let me know if I haven't clarified this sufficiently.

 

Maynard

[Jim]

Sounds fine to me Maynard.

 

So onto the snake oil aspect of things, does it really matter on the other tubes, or are they mostly doing the same thing for this type of amp?

 

Thanks

Edited July 29, 2015 by Jim

[tube fanatic]

Whether tube rolling really makes a difference is subjective.  I'm not a big fan of it unless a tube seems to be excessively noisy, or isn't operating within its intended parameters.  When someone claims that a particular tube is the best available, regardless of the circuit in which it is used, I'd be skeptical.  So, this is an area in which you need to make a personal choice and see where it leads.  You also had asked about the small signal tubes.  Those are self biasing, so no adjustments need to be made if you swap them out.  Only do that for the output tubes.  Also, if you go with matched tubes, you only need matched pairs and not a matched quad.  Keep in mind, however, that unless the tubes are matched using a curve tracer (a rare entity), the single point at which they are matched in no way predicts how they will behave when playing music.  In your case, since each tube is individually adjustable, it may be quite sufficient to use non-matched tubes of the same brand with the same date codes (that will probably minimize the possibility of the production tolerances being vastly different).

 

Maynard

[Jim]

Maynard,

 

I am looking for a multimeter, but they all have the sockets attached to probes. With the amp, it looks like all I need is the probes running into the amp and meter and don't really need the sockets. What meter would you recommend?

[tube fanatic]

Maynard,

 

I am looking for a multimeter, but they all have the sockets attached to probes. With the amp, it looks like all I need is the probes running into the amp and meter and don't really need the sockets. What meter would you recommend?

Jim, I'm not sure I understand what you mean by not needing the sockets.  Take a look at these probes:

 

http://www.amazon.com/1000V-Banana-Multimeter-Probe-Cable/dp/B005QJCRAG

 

The short ends, with the banana plugs, go into the meter.  The long probes are inserted into the (+) and (-) test points on the top of the amp.  It turns out that those actually aren't sockets, but rather just openings in the top plate which allow the meter probes to touch brass posts on the circuit board beneath.  So, they just sit in there (you may have to hold them firmly against the posts with one hand to get a good electrical contact while you adjust the bias pot with your other hand.

 

As far as a meter goes, you can buy them for as little as $7 or $8 although I can't speak for their accuracy.  If money isn't a consideration, a basic Fluke meter (which should last you forever) like this one would be just fine (the multimeter should come with its own set of probes so you don't have to buy them separately):

 

http://www.amazon.com/Fluke-101-Multimeter-Equipment-Industrial/dp/B00JT5RUUU/ref=sr_1_2?ie=UTF8&qid=1438893763&sr=8-2&keywords=fluke+multimeter

 

The meter above does not appear to be auto-ranging (meaning that you don't have to select a voltage range).  So, to set the bias of your amp you would select the 6 volt DC range, which is the lowest setting available.

 

Please post if you run into any difficulties.

 

Maynard

Edited August 6, 2015 by tube fanatic

[Jim]

Maynard,

 

I biased the amp and all I can say is it's night and day. The readings are at 0.35 now. All but one were at that reading and the others were at 0.2 to 0.28. The clarity picked right up on it.

 

My next question is, what exactly are the 6N1 and 6HN1 tubes doing? I've got 3 different sets of the Russian tubes and have been reading a little on other tubes to use. If I do decide to switch out tubes to roll, which ones will make the biggest impact? The EL34, or the 6N1?

 

With the bias, does it work with the numbers being lower giving me the best potential to get that 3D sound, and  with the higher adjustment giving me more linear?

[tube fanatic]

Jim, as far as the tubes go, the 6N1/6H1N are used for line level voltage amplification and phase inversion for the output stage (V1 is the voltage amp, and V2 is the phase inverter).  The EL34s will probably have a much greater impact on the sound you get than the other tubes (although it never hurts to roll some of the others and draw your own conclusion).  As far as biasing goes, you would have to play with it although it's not likely to make much difference since we're only talking about a 5 milliamp differential between the lowest setting and highest.  Keep in mind that the lower setting (where you measure .35V) will keep the tubes running a little cooler than the higher setting.  That can't hurt with power tubes.  And remember that the bias setting only affects what the tubes are doing with no signal applied.  We don't know how the tubes are behaving when music is playing.  So, if you have a bunch of different EL34s around, try them all and use the ones which are most pleasing.  The following links will give you some info about what biasing is used for (although intended for guitar amp enthusiasts, an amp is an amp in terms of basic electrical principles).  I've also attached a link to a nice, short, tutorial about how tubes work in general and other useful information and possibly give you some more helpful hints:

 

http://www.aikenamps.com/index.php/what-is-biasing

 

http://www.humbuckermusic.com/tube-amp-bias-article.html

 

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm

 

Sloth is an expert on push-pull amps, so I'm sure he can add a lot of info on that mode of operation.

 

Maynard

[Guest thesloth]

Remember that you are reading cathode current it will also include the screen current. To calculate actual plate dissipation deduct the screen current from the cathode current reading and multiply by the plate volts. In this amp the screen probably is pulling 5mA.  So if you are shooting for 35mA plate current you will probably see 40mA at the cathode.

 

I would have to look at a schematic and find out more details about the amp and it's output transformers along with looking at some average plate characteristics of the exact tubes you are using. I think the average plate curves from some of the current production Chinese EL34s aren't the same as vintage EL34's. I will have to dig out my notes from when I was designing my EL34 amps.

Edited August 14, 2015 by thesloth

[Guest thesloth]

The readings are at 0.35 now. All but one were at that reading and the others were at 0.2 to 0.28. The clarity picked right up on it.

 

I would go higher. Like I said the screen current is included in the cathode reading. Decrease bias until you get .4 on the highest tube. Or if you are happy leave it where it is.

 

I would like to point out that I couldn't find any plate curve graphs for the Tung-Sol EL34b, the datasheet doesn't include them. I would probably recommend at least trying to run the amp from the 4 ohm tap (assuming you have 8 ohm speakers). The schematic Maynard sent me shows 1k2 load impedance which even though they are running fixed bias seems a tad low.

 

My next question is, what exactly are the 6N1 and 6HN1 tubes doing?

 

Front end looks to be an SRPP for voltage gain and a differential LTP for phase splitting duties. BUT the SRPP is DC coupled to the LTP so it's actually not an SRPP.......more or less it's a common cathode gain stage with an active load. Output is taken from the upper triode's cathode which has a lower output Z then the lower triodes anode. A real SRPP has distortion canceling ability coming from choosing the correct load, the load receives the difference in current draw between the two triodes, making it a push pull operation. A lot of chinese companies find it fashionable to think they are using an SRPP in their amps when they really are not. I have a Shanling SEP amp I got really cheap that has a very similar looking front end, I think they all copy each other.

 

If you would like I could look into this with much greater detail. We can see what different tubes will do in that circuit. Also if you are not scared of soldering you could always change a couple resistors to optimize the front end.

[Jim]

 

The readings are at 0.35 now. All but one were at that reading and the others were at 0.2 to 0.28. The clarity picked right up on it.

 

I would go higher. Like I said the screen current is included in the cathode reading. Decrease bias until you get .4 on the highest tube. Or if you are happy leave it where it is.

 

I would like to point out that I couldn't find any plate curve graphs for the Tung-Sol EL34b, the datasheet doesn't include them. I would probably recommend at least trying to run the amp from the 4 ohm tap (assuming you have 8 ohm speakers). The schematic Maynard sent me shows 1k2 load impedance which even though they are running fixed bias seems a tad low.

 

 

 

My next question is, what exactly are the 6N1 and 6HN1 tubes doing?

 

Front end looks to be an SRPP for voltage gain and a differential LTP for phase splitting duties. BUT the SRPP is DC coupled to the LTP so it's actually not an SRPP.......more or less it's a common cathode gain stage with an active load. Output is taken from the upper triode's cathode which has a lower output Z then the lower triodes anode. A real SRPP has distortion canceling ability coming from choosing the correct load, the load receives the difference in current draw between the two triodes, making it a push pull operation. A lot of chinese companies find it fashionable to think they are using an SRPP in their amps when they really are not. I have a Shanling SEP amp I got really cheap that has a very similar looking front end, I think they all copy each other.

 

If you would like I could look into this with much greater detail. We can see what different tubes will do in that circuit. Also if you are not scared of soldering you could always change a couple resistors to optimize the front end.

 

 

I'd be up to changing things in it a little, but I am far from knowledgeable on everything you stated above. Pardon the pun, but it's all Chinese to me. Layman's terms will work better for me.

 

What I'm getting from Maynard's response and yours is, is that the EL34B's are going to be the ones that I should focus more on for the sound stage and the 6N1's will regulate voltage. If I am incorrect, let me know.

 

Any help from you guys is greatly appreciated. I am ignorant enough with tube amps to sit back listen and take in all information given to me like a sponge.

[Guest thesloth]

Sorry for speaking Chinese

 

 

 

the 6N1's will regulate voltage

 

 

They have nothing to do with voltage regulation. They amplify and invert the small input signal to drive the power tubes. The output tubes (EL34) will generate the most distortion. Increasing current and increasing the load will lower distortion that's why I suggested trying the 4 ohm tap with 8 ohm speakers.

 

It's party time for me I will look into the front end a little more later or tomorrow.

[minermark]

I buy import tubes, prefer chinese, never had a problem.

When the Americas sold out their tube processes, they sold everything overseas.

Does not matter the name on the tube, they all go through a QC/burnin process.

Snake oil is available in this trade also, Cryo ? give me a fkn break.

Iv been buyin/using tubes for 50+ years. ill match my tube numbers anytime with your Cryo process $450 300Bs anytime.

Feel free to pizz away your money on "Quality" tubes, because there are NONE!, and never have been.

The Quality is in one's Ears, not your wallet.

[Jim]

So I set the bias on the amp and it sounds much better. I did have a question on different tube models.IE -6N23P vs 6N1,6H1N.

 

Are these direct replacements for each other? And will there be a different sound if using 6N23P to replace 6N1?

 

Sorry for the ignorance, just have been reading how different people who have this amp are changing out these tubes with each other. I don't see anything where they state they did anything to the amp besides replacing the tubes.

 

There's actually 1 guy who did his own "tube shootout" to see which tubes sounded better than others and did a whole ranking thing. He used 12 different tube styles from 6N1,ECC88,6H1N,6N23P,6922, and E188CC tubes and different name brands.

[tube fanatic]

Jim, I'll have to look up the tube data when I have a few free minutes.  As long as the pinouts and filament current draw is the same, it shouldn't be a problem to swap them out.  As to sound, only you can make that judgment.  Personally, I've not used any of the European/Russian types you mentioned so I can't be of any help there.  Did you find any sites which discussed using those tubes in the MC-10L?  If you do try some rolling, the bias does not have to be reset as that only affects the output tubes.

Maynard

[teknoid]

So I'll depart a little bit from the tube techno-babble and tell you about what my ears heard. Don't get me wrong here the techno stuff is important to understand but not always pertinent to what makes an amp sound the best it can.

 

Back when I was WAY in to tubed kit I came across a Chinese tube manufacturer named Psvane. They were trying to make a name for themselves by replicating the very best of the NOS tube designs. After reading a few positive reviews I pulled the trigger on a full set of their tubes for my preamp (Dared MC-7P) and power amp (Bob Latino St-120). The difference in sound to my ears was so stunning that I rolled the original tubes back in just to verify I wasn't losing my mind.

 

If you have the coin check them out at: http://psvanetube.com/wordpress/purchase/psvane-vacuum-tubes/ Not exactly cheap but many of their products are a lot cheaper than the much sought after NOS versions.

 

Of course with all things tubed your mileage may vary

[Guest thesloth]

So I set the bias on the amp and it sounds much better.

 

Have you tried the 4 ohm tap?

 

 

I did have a question on different tube models.IE -6N23P vs 6N1,6H1N. Are these direct replacements for each other? And will there be a different sound if using 6N23P to replace 6N1?

 

Looking at the datasheets the gain is the same @ 35 BUT the the transconductance is much different. This means that the plate resistance is going to be very different. The 6N23P has a transconductance of 12.6mA/V so the plate resistance will be 2,777. The 6N1P has a transconductance of 4.5mA/V so it's plate resistance will be 7,777. My opinion, they are not interchangeable. I would have to go back and look at the schematic again but I believe the first gain stage looks like an SRPP but isn't, one triode is the active load for the other so I don't see any issues there, but I would be concerned that the LTP phase inverter circuit isn't optimal for the 6N23P. I will look into this some more for you.

[Jim]

It looks like from what I've read that they aren't compatible either.

 

It's looking more and more like I will stick with the original tube types, I just wanted to be sure that there wasn't a better suited tube outside the original.