BRZ FU-50 Amp

Click pics to enlarge. The black wire is Canare L-2B2AT.

Review: BRZ FU-50 SE Amp, Part I
Letter from Shenzhen (23-7): Is the "Little" 300B a 300B at all?

Part II is very short, a Capacitor change for the better, embedded in another article.

Also, consult this article, which shows that the amp can do a much better job with even higher efficiency loudspeakers!

Part III covers 80 rectifier and even WE 274B use.

This is a long delayed “formal” review of an amp I have long used and have “previewed” before (here). It’s a highly deserving amp on its own and a tremendous bargain. Before, I had to write about cables to prep for my Eastern Transmission Audio Preamp article; just as I have to write this article to pave the way for my coming article on moding my Preamps, which is highly fascinating, to say the least.

The Reputation of the FU-50 Mostly in Chinese media, FU-50 has been touted as the “little 300B” because it was said that when operated in triode its curve is almost the same as 300B.

https://m.tb.cn/h.UK1tryS?tk=Au3xd8ffgnn

TWO Versions This amp is widely available everywhere, under many vendors. The FU-50 is operated in Triode mode, said to yield 8 wpc. There are 2 versions with different drivers. I deliberately chose the pentode driver version, for reasons I alluded to here and here. The Soviet 6J8P (6米8) has western equivalents, like the 6SJ7 (a classic WE era 6J7, with different pin-out [without the top cap]; so, in a significant way, this design bears a resemblance to the WE 91A circuit, which has the 310A/6J7 driving 300B) that is favored by many SE amp designs (like my Softone/ICL amps, here and here). There is also a version that uses the double-triode 6N8P (6SN7) as driver, but that’s a different animal, which you might like if you own good old stock tubes that are now very expensive (I do, but not here in China). The 6SN7 design brings it too close to many other 300B amps, like my Sun Audio (and its myriad clones here in TB). You, however, depending on the tubes you have, may want to choose otherwise. At around RMB 900, it's a bargain.

Build Fabulous! It’s a very beautiful amp, and smaller in size than usual (though slightly larger than my Sun Audio and ICL). Better than many “high-end” offerings if you ask me. The milled aluminum is just luxurious. Inside, the amplifying parts sit on a high-quality circuit board, with good parts and wiring to the rest. Yes, a choke. Nice. It’s also gratifying to see that, in contrast to the others, the amp actually uses a quality signal cable, my preferred (and dirt cheap) Canare L-2B2AT! Great! On the other hand, if you DIY, you can buy just the board, cheap!

Stock Tube Sound It comes with a Chinese 5Z4 instead of the Soviet 5U4M pictured (yes, the TB page says this in small print at the bottom). It comes with Soviet 6米8 and very well -built Beijing FU-50. Sound was very nice out of the box (perhaps slightly lean).

Reliability Absolute. This amp runs for umpteen hours a day, with no problem. I use it with my Beydas LS3/5A.

Issues None. Which is why I use it as routine. My APPL suffers from a loose socket problem that emits annoying popping noises occasionally, not completely eliminated even with tube shield on (here, which however, is not present in Shawn P and R Salamat’s samples). Sonically, it’s a different matter, as below.

Tube Rolling I have 3 amps here. The Aosibao came with a Soviet 5U4M, which I sometimes use in the others. For shared use, during 11.11 I bought what I considered to be reasonably priced rectifiers here: 80’s Philips 5R4WGA (GT bottle; RMB 164); early Chatham 5R4WGA (potato masher; RMB 145 - this is a great bargain!); Tung-Sol ST 80 with adaptor (RMB 244 + 20). I may write an article on rectifiers later. Suffice to say, all of these sound better than the stock Chinese 5Z4. The stock Soviet 6米8 is actually quite good, steady and spacious in sound, though with smaller images. My sub, the Raytheon 717A (RMB 400 for the pair) sounds very different, as it imparts more texture and solidity to the sound, bigger imaging too though the soundstage is perhaps not as deep. Too bad I don’t have the WE version here (used in my Yamamoto 45 amp). I finally re-capitulated too and got the Soviet 50’s FU-50RY (RMB 140 per pair) and they further improved the sound in terms of texture and dynamics. So, you can see that, even discounting the costs of the rectifiers, which I use in all 3 amps, there is still a premium to maxing out the potential of the amp but it's small (RMB 540, which is a little more than half the price of the amp). It should be said that the stock tubes are decent. Better tubes improve things a bit, but perhaps not on the transformative level, so one should buy wisely. For the rectifiers, the 5U4M has a drier sound (not nearly as good as their ST bottled ones). The 5R4WGB is significantly sweeter; the 5R4WGA (potato masher) a little more detailed and forceful. I mostly alternate between the two. The 80 with adaptor is a totally different animal - softer but so rich and sinewy; I sometimes enjoy it at nighttime.

vs 300B So, is this a small 300B that is deserving? Well, yes, but it depends. Even in stock forms, the APPL (which, despite its quirks, I rate very highly) sounds a bit more organic and luscious, at a little more than twice the price. With all the tube upgrades, the FU-50 closes the gap, but not completely. Tonally, the 300B is still more sophisticated. Although the FU-50 is rated at the same 8 wpc, I don't think so; power is noticeably a little short of the 300B, and its clipping/saturation are somewhat less benign than the 300B. But it’s very revealing of what’s upfront (my next article on my Preamp mods). Suffice to say, at its best, for not much money, with or without tube upgrades, it’s a winner. There is NO SET amp that can put out as cheaply as much power, and with as much finesse (I'm pretty sure it outshines SE EL34, 6L6 etc). If your budget is limited, this is a prime consideration. Even if you can spend more, this is a great lesson on how much can be accomplished for so little. Mind you, I’m comparing it with the APPL 300B, which I rate higher than many bigger named 300Bs (but quirky!). In fact, the more I listen, the more the BRZ seems to sound like the usual DHT amp, whereas the APPL sound has qualities that are hard to describe (may be another article). So, an average el cheapo 300B might have a harder time facing up to this amp. All this is based on the harder to drive LS3/5A. On my more efficient Sansui floorstander, the FU50 faces the 300B on more equal footing, with an exciting drive and transient prowess, but I haven’t done that in a while (initial impressions)

There have been significant changes in my system. Simple cable upgrades to my Preamps (article to come) have brought them to much higher levels of performance. Also, the addition of a pair of Xinshi 新时 597 passive “supertweeter” has also snapped things into focus. The system is highly satisfying. Previously, occasionally I wondered if the BRZ is a little on the lean side. No longer. I may yet to do a little cap change to see if I can extract even more out of it.

Recommended if you have tight budget and efficient loudspeakers, do not have too much real estate and prefer a tube sound that is closer to neutral rather than obviously smoky or cloying.

Keep in mind, greater than 90% of my time are spent with this amp (I listen for more than 10 hours a day). If it's good enough for me, it may also be for you!

Schematic