Yaqin MC-84L Tube Stereo Amplifier Review

[mhardy6647]

A fully tubed stereo amp would have at least 3 tubes. One driver tube like 12AX7 and 2 output tubes like EL34/KT88/6BQ5. An amp like this will have 5 to 25 watts per channel. The term hybrid usually means tube driver and solid state output. Also you are not likely to find any 100 watt amps for less than $1000 even used.

Single-ended, it can be done with two (per channel): voltage amplifier (triode) and power amplifier (in some of our cases, this is a triode, as well).
PS Yes, pentodes could be used instead. Even kinkless tetrodes in the output stage, were one to insist.

Over at Audiokarma, one owner indicates 30-40 hrs to break-in, 100-200hrs to open up and let the musicality shine…..

Oh... they'll know, all righty.

 

[biker29]

That is per channel I guess? Or total?

For two channels the minimum number of tubes. These are called single ended amps.

 

[JoelEco]

The good point though: Here’s an opportunity to take a close look at the bottom end of the SINAD scale finally

View attachment 400643

I purchased a MC-84L 2021. The unit came with Russian 6P14 and Psvane ECC83 tubes. Distortion and noise specifications is part of the sound equation and more so with vacuum tube amplification. It is a wonderful sounding amplifier and with the right speaker, interconnect cables, and good recordings, will emulate the sound of live musical instruments. That is a big accomplishment for any electronic audio product. This amplifier is a bargain at $599.00 retail.

 

[JustJones]

That is a big accomplishment for any electronic audio product. This amplifier is a bargain at $5.99 retail.

Fixed the price for you.

 

[mhardy6647]

It's true that a SE stereo amp could be made with three tubes... depending on how one defines a tube.

The 12AX7 is a twin triode - two vacuum tube elements in one envelope. Is it one tube, or two? Depends upon one's point of view.
That said, and as @biker29 said, one 12AX7 and, e.g., two 6BQ5 will give one a nice little stereo amplifier of ca. 4 watts per channel.
Sort of like a Maggotbox Magnavox 8601 console amp, although they used a 6EU7 for the twin triode.
The 6EU7 is a sort of interesting tube - if memory serves, it is one of several tubes RCA produced to be deliberately pin-incompatible with another popular tube type (the 12AX7). Otherwise, it is essentially, operationally, a 12AX7, albeit supposedly designed for lower noise and microphonics. Note the single 6.3 VAC heater of the 6EU& , as opposed to the center tapped 12.6 VAC heater (essentially two 6.3 VAC heaters in parallel) in the 12AX7. Good ol' RCA.

Tube data from Pete Millett's site: http://www.tubebooks.org/

 

[JSmith]

"the design is very clever"

I'd say poor rather than clever...

I purchased a MC-84L 2021. The unit came with Russian 6P14 and Psvane ECC83 tubes. Distortion and noise specifications is part of the sound equation and more so with vacuum tube amplification. It is a wonderful sounding amplifier and with the right speaker, interconnect cables, and good recordings, will emulate the sound of live musical instruments. That is a big accomplishment for any electronic audio product. This amplifier is a bargain at $599.00 retail.

Uh huh...


JSmith

 

[jayapple]

There are good tube amps and there are cheap tube amps. There are no good cheap tube amps. That's a sad reality.

There are also some inexpensive and decent amplifiers.
However, it is not a pure tube amplifier, which has a triode circuit, generally two or three small bulbs, and it is very cheap, and the resolution is much higher than the tube amplifier.

 

[ROOSKIE]

Tube amps usually refer to amps with Tube output stages. These amps have a tube driver (preamp section) and solid state amplification. If you want tube sound the amp section needs to be tubes.

Nice bold. Seems like you did not read what I wrote at all. I essentially stated all of this in my post. Those links were aesthetic options as clearly stated in the post above the links to the Dayton amps.

"If you just want that tube visual look try one of the Parts Express, Dayton amps that use a tube pre-amp like these 2. They have more features and are more powerful."

 

[johny_2000]

I would like to see the schematic diagram of a Push-Pull pure Class-A triode design with a transformer output. If anyone has it, please post it.

 

[ROOSKIE]

It is a wonderful sounding amplifier and with the right speaker, interconnect cables, and good recordings, will emulate the sound of live musical instruments. That is a big accomplishment for any electronic audio product.

What interconnect cables are the right ones?
Why would the fidelity issues most tub amps provide, such as extra harmonic distortion, low power output so likely lots of soft clipping, likely poor channel balance and high levels of crosstalk & likely altered frequency responses due to variation with speaker impedance, emulate the sound of live musical instruments better than an amp with none of the listed issues? I do agree a good recording is key

Enjoy your journey, though this idea of low fidelity devices sounding more real makes no sense to me at all.

Of course I love fresh squeezed orange juice made from the real fresh oranges and a juicer and absolutely have met people who do not like it and prefer reconstituted, cooked/pasteurized orange 'juice' and water from a can or paper jug. I generally equate a tube amp or other low fi payback device like a record with that. Totally cool if that is your jam but I think is a mistake in the long run.

 

[SIY]

I would like to see the schematic diagram of a Push-Pull pure Class-A triode design with a transformer output. If anyone has it, please post it.

"Pure class A triode" is generally a very poor idea. Take something already inefficient, make it far more inefficient, and achieve nothing in performance.

If you look up the old Marantz 9 schematics (they're all over the web), you can see how to pump in a lot of power and get very little out.

 

[mhardy6647]

I would like to see the schematic diagram of a Push-Pull pure Class-A triode design with a transformer output. If anyone has it, please post it.

"Fatboy" 300B Push-Pull Amp

Power supply:

If I am reading Pete's description correctly, the default is to bias the outputs into Class A. He uses the term "heavily" -- not sure what he means by that. I think of Class A operation sort of analogously to virginity. It's kinda binary, you know? It is or it ain't.

 

[aslan7]

I seriously believe that people who like tube components regard noise and distortion as assets. That explains the favorable Amazon reviews.

 

[Blumlein 88]

I seriously believe that people who like tube components regard noise and distortion as assets. That explains the favorable Amazon reviews.

I don't have much experience with some of these newer affordable designs some of which are simply incompetent. So maybe on Amazon reviews. However, people have liked tubes for a long time. Plenty of good tube designs don't have levels of noise you'll hear in use or distortion at levels that matter with music unless they are poorly matched with the wrong speakers.

 

[AndreaT]

Just a thought: the majority of flat screen TVs, the most expensive one with oled screens, are almost never properly calibrated for color (too vivd, red push), luminosity (usually excessive) and sharpness (way too high). Do average viewers and listeners like distortion of the original? Is the most desirable mimesis for the masses a less faithful image of what it could be? Does the fast food lesson carry on into music and photoplay reproduction? Ah, I will try to find and read again my books by Vilfredo Pareto about the 80/20 theory of the elites…

 

[Bob from Florida]

"Fatboy" 300B Push-Pull Amp

View attachment 402273
Power supply:
View attachment 402275

If I am reading Pete's description correctly, the default is to bias the outputs into Class A. He uses the term "heavily" -- not sure what he means by that. I think of Class A operation sort of analogously to virginity. It's kinda binary, you know? It is or it ain't.

If you run the numbers the output 300B's are biased at 48 watts per pair. Each pair is 72 watts max which yields 66.8 % of max or the usual close to 70% recommended for class AB operation to minimize zero crossing distortion. Pete does say the interstage transformer will drive the 300B's into positive grid current - A2 operation. But if you do that distortion goes up with the power increase.
Nice job - I love the volt meters in the tube envelopes. Have to get some of those to use in my next build - if I can retire and get back to building stuff.

 

[mhardy6647]

I love the volt meters in the tube envelopes.

Those are interesting... I thought they were photoshopped until I read the text!

PS Thanks @Bob from Florida for doing the homework on the operating points for the outputs! I was spread a little thin yesterday (grading students' midterm exams), but the bottom line is that I was too lazy to think about it!

PPS not quite on-topic (yeah, I know, right? ) but a fellow on the Polk forums built a snazzy bucking transformer (to lower input mains voltage for vintage equipment expecting somewhat lower AC supply voltages than typically found in the US in 2024) using some adorable little AC voltmeter modules from Amazon

Bucking Transformer For Vintage Receiver

I built this bucking transformer for the owner of the HH Scott 399 with Scott 355 FM multiplexer I am refurbing. A bucking transformer reduces AC line voltage.

forum.polkaudio.com

 

[Barry_Sound]

Any word on the sound besides measurement? Does it actually sound badly distorted or what?

 

[mhardy6647]

Well... if one looks at (dare I say it?) other forums and reads between the lines a bit -- the big issue flagged by some other folks is the cheap, crummy tubes amplifiers like this ship with*.
Now... I am not a big proponent of tube rolling - at least, not for its own sake - but I wonder if some of the channel to channel anomalies that I think I remember seeing in the original test data might have traveled with the specific tubes in one channel vs. the other? Mind you, I am, at least at the moment, too lazy to go back & carefully read the review - but I probably will.

I will say that swapping tubes from channel to channel to see if one (or more) of the tubes is root cause of an "issue" is a time-honored troubleshooting technique. Now, it could be argued that a brand new component shouldn't require any troubleshooting - but we are talking about a 600 dollar vacuum tube amplifier.

The sad and ironic part of this particular amp model -- 15 or 20 years ago, as Chinese hifi components were just beginning to acquire some legitimacy (at least in the US), Yaqin was a premium (relatively speaking) brand. They produced (i.e., the brand name was attached to) some attractive and seemingly well made, straightforward amplifiers (mostly integrated amps) that were reasonably priced (not cheap) and had generally good reputations.

Conversely, this MC-84L seems to be cut from the same bottom-feeder cloth as so many other (too) inexpensive audio components these days.

___________________
* forgive me ending a sentence a preposition with for.

 

[Saponetto]

A SEP-SET amp is an almost well defined thing that has fixed components that should work decently on 80% of tubes, thus collapsing time and build expenses.
Push-Pulls are forcibly in need of a good-will man that selects the biasing resistors and tests the valve behavior, thus ncreasing time and build expenses.

This is a classic example on how matching the push-pull needs with the straightforward assembly time of a SEP-SET just creates monsters.