Boyuurange / Reisong A50 300B Tube Amp Basic Mods Part One
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- Опубліковано 20 сер 2021
- In this two part video, we start the modification of this amp by working on the power supply. The bones are there, but the design is poorly implemented which limits the power and cleanliness this amp is capable of.
We do some basic changes which increase the output voltage, still well below putting any stress on the tubes, which brings out another 1.5W of power. This gives the amp a much more authoritative sound at all volume levels, by soldering in 4 inexpensive parts and replacing the rectifier tube with the very popular, slow warmup 5AR4.
Please see the next video in the series as I split this up into two parts. I will be uploading schematics and a BOM to my website once I have finished the series. www.skunkiedesigns.com - Навчання та стиль
I'm amazed by how you manage to take some of these things that are at a level most wouldn't even bother, and then turn it completely around.🙂
"We're fixin' to see whether that's true or not" I am not an electronics guy but I am an audio guy, and again you have impressed me with your ability to clearly explain and show these improvements in a way that is understandable to the layperson.
Very interesting thank you! I'm following this like a detective story. Also, I'm impress by the clean layout (except for the big metal resistor) and wiring of this amp.
It is so great to hear the great improvement in this 50 amp
Glad you are enjoying it!
Expert, thoroughly talked through.
fantastic most people talk about how it's done you actually show us.
Thanks
I've just performed all the mods in this video to my A50. Thanks Steph, you're crystal clear in your explanation and I'm grateful.
Cascode mods next!
The cascode is where the magic really happens.
Thank you for sharing, very interesting and informative, just uploaded a few of my hand crafted tube Amps. I enjoy learning more about the world of tube Audio!
I'll check it out!
Love this channel! I’ve learned so much!
Glad you enjoy it!
Great videos, I'm learning a lot thanks!
Really great video, very detailed and helpful...
Glad you enjoyed it!
I bought my Boyuurange / Reisong A50 III in May but just got it in August. I have the same 600M speakers. Excited to see how you test and analyzes equipment. Please post all possible scenarios for A50 upgrades.
I plan on it :)
Nice Work…keep going, very interesting
Thanks, will do!
Exciting project.
What is reasonable voltage ripple for B+ since my amp has around 16mV. I read somewhere on the internet said reasonable value is around 150mV or something. What is the total value for choke in series? For example 5H/300mA/150ohm would be 10H/600mA/300ohm? I was looking on the web that said double inductance but didn't see anything about DC current and Resistance. If you add filter cap between 2 chokes, would that drops the total of choke in 1/2 which it may change the max DC current and resistance.
They are 32 ohm chokes, 64 ohm total.
Hi. Just found your channel - very interesting. I had a Boyuurange A50 for a bit and then sold it for a Willsenton R8. I really liked the mid range of the A50 but found it to be a bit grainy/noisy and lacking bass. The R8 (push/pull 45 wpc) was definitely cleaner and stronger, but lacked the sweetness that the A50 had. So I sold the R8 and just recently received an Elekit Tu-8600 300B tube amp that I love. The Elekit claims 9wpc. It's super clean and transparent. Still a bit lacking in the bass but I think that has more to do with my speakers that have 8" drivers... I'll probably add a sub.
Would be interested to hear your thoughts on the Elekit Tu-8600. Do you have any experience with Elekits and this amp in particular? Any suggested mods?? Any experience with using a low-powered SET amp with a subwoofer?
Thanks!
No experience with them, I'd be shocked if it actually makes 9WPC and the bass is the tricky part with a tube amp. I'm using speakers with a lot smaller drivers and a good amp has nice bass so I wouldn't jump to it being the speakers. Did the R8 also have weak bass? As far as a sub, look for models that have speaker level inputs.
Hi, I'm really interested in doing some of these mods myself. I was wondering what the capacitor is that you added to the choke?
You might try adding a Ultra path capacitor on each Channel from the power supply to the cathode of the output tube. You will have to isolate the power supply from each Channel by using a separate choke filter... The concept comes from a early designer who was discovered by the man that electraprint... I ran into a on a website from Thomas Meyer called vinyl saver wrong spelling but you'll have to look
Cool idea, the DIY amp uses a split rail PS with two chokes. Do you have a link to more info?
Can I convert an El34 single ended amp like the Lao Chen EL34 to a 300B SET amp? I’m wondering aside making sure the B+ voltage is high enough to power the 300B.
You also will need two separate 5V filament transformers for the 300B tubes and different output transformers. Also what ever circuit was used to drive the EL34 tubes likely won't drive a 300B.
Can the 5AR4 rectifier tube be substituted for the original 5Z3PAT as a drop-in replacement? Or do I need to make modifications you mention - the bypass resistor and the filter capacitor between the two chokes to use 5AR4?
Yeah, you can just drop one it.
@@SkunkieDesignsElectronics Thank you for your reply. Another question. The original 5Z3(PAT) rectifier has 4 pins on the base. 5AR4 has 5 pins. Something is not connected to one of the pins?
When I want to open the hole on the pcb I simply use a toothpick. It is handy when hot modding a board that is already wired in.
hi, thanks for this great series. Exactly what is a 'choke' doing?
The choke or "inductor" helps filter/smooth the AC while also adding for DC resistance between the filtering caps.
i wish there was bit more specific info on the capacitor part #s on the BOM, is the coupling cap that you put in a film or an electrolytic, the one you took out looked like a film but im having a hard time finding what it was you put in, part #s for those too would of been handy. I can make my way around with an iron but specing parts is still at a loss for me. I would really like to do the mods up until that point at the minimum with the different tubes youve recommended, the jumper, the 47uf and the .33uf (edit-the final diagram has a 0.33uf but in this video you say .56uf, if i just want to do up to this can i use the 0.33 without more mods or do i stick with the 0.56)
I clearly need to do a video on how to navigate parts.
The problem with listing part numbers is specific part numbers are short lived and with supply chain issues, they might be out of stock for over a year, which identical spec ones are in stock. When I have done this in the past, then I get endless emails about " I can't find this specific part number".
And honestly on this amp, what makes the real difference is the rewiring of the front end tubes. The other mods probably won't even be audible until that is done. And yes the right part is an audio quality film cap 0.33uf. you never use an electrolytic cap for coupling.
@@SkunkieDesignsElectronics thank you
👍
Is all the curent needed to be rectified in this amp done by the rectifier tube, or is there a split that runs some cicuits by a bridge rectifier?
All of the power goes through the rectifier tube in this amp.
@Nihil1st1347 the 300b’s filament run on DC. Hence those 2 bridges. Not looking at schematic. But from measurements.
Very nice enclosure at the first look, Where did you buy it?....
It's a commercial amp from China. I'm just modifying/upgrading/fixing design flaws with it.
Hi there. I have recently purchased this amp with your mods already done. I noticed that it has hum even with inputs shorted . Original tubes except the rectifier. Would you have any ideas what to look for? What to start with? Thank you. Regards Paul.
Yeah, look at the tube heater circuit. My guess is they did something wrong there.
Will do thanks.@@SkunkieDesignsElectronics
What about a NOS RCA or similar 5V4 as opposed to the 5AR4 recommendation?
That would work with just a slightly lower B+ voltage
Thank you! I'm doing all the mods to my Nobsound now, and am look to the A50 as my next step later this year. Had already invested in some great NOS 6SN7's and 5V4's for the Nobsound and was hoping to be able to swap those over to save some cash. Love the content and tips!
Hello, I am enjoying your A50 videos and subscribed. Would a New Genalex GZ34 / 5AR4 work well as an upgrade in the rectifier location with stock internals on the amp? I don't know how to do electronics yet but I would like to tube roll. I am also looking at Psvane CV181-T MKII (6SN7) and Electro-Harmonix 300B or the Gold Lion 300B. Thanks for anyone's help here! Cheers
Not likely to make any big improvements, the amp as wired is too flawed unfortunately.
@@SkunkieDesignsElectronics Thanks for your reply. I ended up having your mods done on the amp and I love how it sounds! I am really enjoying it now. ☺️
My A50 has a 115V sticker in the back. I did the mod but the 5ar4 arcs and blows the fuse. Do you think that It may be due to the amp being fed the 120V line voltage instead of 115V?
What 5AR4 did you use? If it was a JJ, that's likely the problem.
@@SkunkieDesignsElectronics that was my first thought as well but I was using a gold lion tube. Then I went down to guitar center and I bought a Russian one, that worked a bit better but eventually did the same thing. Now I ordered a tung-sol. We’ll see how that works.
@@andyermolli3226 A gold lion 5AR4 is fine, there is something else going on. I would unbypass that first resistor and try it like that with a new tube. Also did it arc on powerup or after it was running?
@@SkunkieDesignsElectronics I will try that. The weird thing is that I used it for hours with the Russian tube just fine. Then later when I went to turn it on again later it arced. That was at power up.
@@SkunkieDesignsElectronics ok removing the bypass has no effect except this time it didn’t arc but it just blew the fuse. The fuse that’s in my copy is a 4A fast acting 250v. What fuse did you have in your copy?
I hve done the basic mod, bypass the 39 ohms and added 47uf cap btw chokes. Then I fitted a NOS Amprex 5AR4, enjoyed noticeable difference in audio performance, Bass was better, overall not as laid back. However it is less warm overall....as trade off. One worry, the Power Transformer gets very hot after 2/3 hours of play. Is this going to be an issue?
Have you checked the voltages? It's possible you have a 110V wound transformer on a 120V line voltage. Many power transformers run pretty warm to hot. Is it too hot to touch?
@@SkunkieDesignsElectronicsits not skin burning hot, yet exceptionally hot. Can feel the Power Tran has hint of vibration too. Wall AC is 230v Singapore. thanks for quick reply....and expert suggestions appreciated. Is it the 39ohms bypass causing it？
@@thomasleong9401 It never ran warm before? And again, I have no way to know what transformer your amp has in it, might be a 220V or a 240V primary. These amps seem to be all over the place on which one they use. If you think it's too hot, you can unbypass the resistor. Again, without checking the plate/internal voltages, you really don't know.
@@SkunkieDesignsElectronics I ordered with 230v Transformer. After two weeks of playing it, getting the tubes to run in, this mod to increase the voltage interest me！ It did improve the playback solidness of playback. If there is someway to reduce the hot PT would be great. My experiences are towards guitar amps repair and upgrade and lesser knowledge on hifi amp. Though I recently repaired one Audio Note Kit amp motorboating, and a Marantz 8B vintage hifi amp. Got hooked with the sounds,so bought this A50Mk111, it is enjoyable amp. I suspect the way it was set up by manufacturer intentionally, to play cool with warmth and to preserve longevity Your mods are appreciated, yet may hve to balance longer hours of playback and its long term stability. Will replacing PT upgrade makes it more comfortable. Out transformers are all fine, in terms of heat only the PT is my concern.
@@thomasleong9401 just because you "ordered it" with a 230V transformer, doesn't mean that is what is in it. Again you are working on the amp and are there. The one I modded didn't get hot but was a 120V model. And unless you actually measure the plate voltage, I have no clue what voltage things are running at. Good luck with it.
Better capacitors to make a big difference
Hello. Could you please activate the translation of your video ? Thank you very much for the quality of your videos :)
Merci :)
I will try!
Nice build amp but I wonder why did they mount the shokes so close to the power transformer there is loads of room further away. Inducters so close they may pickup induction.
I use mundorf supreme 600v type copple caps. I have made a 6550 pp ul amp is some other then this se 300B amp.
Good point!!
Is this the BoyuuRange REISONG A50 MKIII, 2 or 1?
MK III
@@SkunkieDesignsElectronics thanks
Тоже такой купил. Я заметил низкочастотный гул в колонках. Гул не зависит от положения громкости. Он всегда одинаков
Был при включении в одном канале, потом пропал ,поменял местами 300б
Hi there again, I have taken some measurements with the stock rectifier and I get 421V at the B+ and 408V at the output tube. Essentially all my DC voltages are an almost exact match to your measurements with the 5Ar4 but mine are with the stock rectifier. Is this what I should expect? I have already done the basic mod.
I honestly don't know what is going on exactly unless they put a different transformer in your amp. If the volts are right, then you are good :).
@@SkunkieDesignsElectronics I suspect that they saw your videos and changed their design!
Got all excited about finding a real pristine as new one locally and bit. Turns out the darned thing is 100 volt model. Paid about half or less what a new one would have ran. Disappointed when my email won’t go through to China Hi-fi to ask for buying a correct US mains transformer. I may inbox you, if you have any more ideas, don’t want a variac or step-down married to this thing.
That's one of the problems with this Chi-Fi gear, you can't get parts for them. The only other option other than setting up a 20-25V bucking transformer/reducer married to it is to hack some other power transformer. And then without ALL of the mods in my series, these aren't even a decent performing amp.
After more probing it’s 110 mains. But still junk with the initial 5AR4 mod, American 6SN7 and K42y Russian PIO caps. Variac 110
All those "easy mods' will not fix the problems with this amp, until you do the cascode rewire, that other stuff is a waste of time. It's common for them to ship 110V units to the US, many sold on Amazon have them and the best solution is find one of those APC voltage regulator boxes and set it to 110V or make up a bucking transformer.
@@SkunkieDesignsElectronics just happen to have a few Hammond 166N6 filament transformers. Will do the cascode and carry on. Thanks for the series!
Luckily only had to buy a few resistors.
Also want to try a couple Ohmite L25J1K0 1K 25 watt ceramic ww
I did a recent video about using 50W resistors from amazon and remote mounting them with thermal double stick tape to the side of the chassis.
Those two 25W resistors should be clamped closer to the chassis and not on the PCB, that's a weird mistake.
Maybe try non-inductive, non-magnetic power resistors instead of the sand cast type....
I'll look into that, who makes them?
@@SkunkieDesignsElectronics Mills Wirewound Non Inductive from Parts Connexion or Sonic Craft. You could parallel two 12W or 10W resistors. They are pricier than sandcast but worth it in cathode bias apps.. Another one is the metal clad Riedon resistors..
@@SkunkieDesignsElectronics Not sure the max power rating you need here, but check these: Duelund Standard Graphite Silver Resistors 5w and 10w
Pathaudio Resistors 10 Watt 1%
Mundorf M-Resist Supreme 20W
Powertron FPR2-T218 30W Metal Foil Resistor
Jantzen 10W Superes resistors
@@mfr58 I'm only seeing these in 100ohm and less. These need to be either 880 or 1K (plan to try both of these values)
@@SkunkieDesignsElectronics Yes, you're right, I can't see higher values. How about
RES-M1345- 12W MRA12 Mills Resistors, they have a range that you could make the values you want.
0.067 amp on the 300 B cathode / heater is a good spot to be HT 410 volt / 410 x 0.067 = 27.47 watts of plate dissipation max is 30 watts should should heaps better 27.47 watts / 30 watts = 0.91 %
It's actually 0.067 amp with 343V across the tube (410v-67V at the cathode). To get it to 90% with this transformer would require converting it to fixed bias and I don't feel this china 300B would survive with over 400V in a fixed bias setup + this frontend would never be able to drive it.
@@SkunkieDesignsElectronics jj 300 b good
The one thing i hate is seing those PCB on a tube amp
Why is nit you spot the missing cap between chokes that lowers the ripple by 95% ? What kind of Electronic Techs come out of China? You plainly see it and they dont?!