Thanks for sharing your stellar work here. I can tell as I am an electronics engineer, with experience working on tube amps for satellite uplinks. Some of them at 1500w at 14Ghz. Fridge sized. Lately I have also DIY'ed a few tube guitar amps (mostly 50's fender clones, but modded to be a bit less hummy) and also made a clone of a "cracking" headphone amp that turned out very well. Following your channel as I am looking into diy'ing a power amp, perhaps a 300B one... Keep up the great work!
I own this amp for last 5 months. It only played for 3 weeks. I have received 3 sets of tubes from China Audio so far. All of them died.The last set is 5U4GB EH tubes (made in Russia). I gave up and connected back my DIY Aleph J (FirstWatt clones). I really hope you will make this amp to be stable and play again. Good luck and thanks for your awesome work.
I had just bought the R300 and still waiting on its arrival. Then I found your recent videos. LOL. You've got me holding my breath and on the edge of my seat. I've been wanting my own 300B amp for years. I've got a modest budget for stereo gear. I still have hopes that this amp provide a good starting point that will deliver that 300B sound. I love modding my equipment so I'll be watching closely and probably following along. Thanks for tearing into this one.
Wow this was cool. Its like the original rectifiers were damn near just for show. Im sure your revised power supply will yield great results. It will at least be more stable and reliable. They seem to over complicate things and maybe dont quite get how to design a circuit right. Im really interested in seeing where this ends up. Great job as always, thanks.
I agree, they're obsessed with appearance. Plug-in solid state rectifiers with thermistors would fix it quickly but if I'm buying a tube amp, I want tube rectifiers.
Your work is truly remarkable ! But I'm starting to cringe at the prospect of changes that are likely to be too big for my taste ... But I'm going to hang in there and try to understand as best I can and judge whether it's all within my capabilities or not. Thank you for such an enlightening analysis of how to make this machine better :)
Super interesting! Eager to see what this mod does to signal respons. Do you think that the global feedback implementation in this amp design may be contributing to the weird square wave response?
I'm not familiar with the 274 rectifier so I looked it up and i agree they are badly abusing it and that the first smoothing cap is probably killing the 274's.. It was chosen for it's looks and little else.The 5AR4 tube solves the slow start problem and is a pretty rugged tube if you follow the rules by reducing that first smoothing cap..
This is one of the reasons that I always ask individuals who want to use Emission Labs 274A/B rectifier tubes if they know the value of the amplifiers first capacitor. Using more than a 4uF cap as the first cap with a 274 is a big no no.
The mysterious diode is essentially a support for the rectifier tube to prevent the entire current from flowing through the tube during power-on. The large charging capacitance demands a very high current at power-on. It should be considered to slow it down slightly with a small capacitance. Otherwise, it does not affect the sound......thx for the vid
But the entire current does flow through the tube for it to be able to make it to that diode. They are in series. Series diodes improve their voltage handling, parallel ones increase their current. And large first caps impact a tube rectifier in more ways than just inrush current.
@@SkunkieDesignsElectronics You absolut right!.....thats my fault, because I saw the video in 480p mode.Thx for your comment.....or I would never know I need glasses.
Seen it before ............rectifier +diode ............questions ? YES !..............but one fact remains that the rectifier has a galvanic separation and an internal impedance , both conditione nevertheless the sound . Normaly a delay that applies the high voltage when the heaters are fully warmed up should not switch the HV to the circuit that way , only so with solid state diodes ........but with DIRECT HEATED rectifiers the filaments of rectifier tubes must be switched on/off ! NO worries with indirect rectifiers as they have a delay of themself ... Another mistake is also seen on commercial tube amplifiers is .... 1) The warm up period only switches the inputs/outputs ............ 2) The HV must be shut down before the heaters of the tubes are shut down and the power supply capacitors must be drained before switching off the heaters ....... Both cases/design errors do not protect against stripping of the cathodes of your precious tubes ...... Correct start up and correct shut down expands the usefull life of tubes by several times . 20 000 H on a 211/845 and almost 100 000 H on a 12AX7 etc are not uncommon when used respecting this or never shut down the amp ( BBC policy= never shut down their tube amplifiers ) .............only with nos tubes ! For example WE 408a and other types ............12 years continous use on test bank ..........Still within specification ! equals 24 hours times 352 days times 12 years ........calculate the Ihours under controled conditions within normal operation conditions ..... In 1924 ............A standard 101D /F has a lifespan of 40 000 /60 000 hours ..........( thelephone repeater tubes ) In reality , commercial practice ,manufacturers need selling tubes as much as they can at roaring prices , so WHY protect tubes .............? Now I am curious watching the next part of the video to see what you find out about the power supply ..............nothing asthonish me anymore today with the boom of many but not all badly designed asian tube amplifiers . Thank you the upload and sharing .
@skunkiedesignselectronics - Thank you for your detailed reviews. I find them helpful and informative. What is your take on the headphone output for this unit? Is it similar to Wilsenton R8 or better?
I could be wrong but like to have a shot. It looks that the tubes are in parallel to up the current available, and the diodes are blocking diodes. However, the new power supply design will work just fine.
the diode i believe makes it kind of a hybrid tube and diode rectifiying. increases supply voltage because you cant really parallel two tube rects to make it a bridge
Interesting Stephe! I might be a good plan to flush mount the socket for the future 5AR4's, as they may look weird in the current low position. Also, would it be beneficial to upgrade the existing choke to a better (or similar) quality as the new Hammond choke?
@@SkunkieDesignsElectronics A shame the two rectifier tubes are in parallel, it would be nice to make a dual rail PSU. Looking at the schematics, that may be challenging but it would be a chance to get rid of the crazy big 330uf cap 😛
Thank you so much for this much awaited video...I've been thinking of getting the W300B amp, but I I have to admit that I felt a bit intimidated on the potentially necessary modifications, I am new to this, but I just recently recapped a Sansui vintage receiver, and the end result was favorable, Now,, I'm working on a vintage Marantz tuner. I really hope to be able to make this modification, if and when I get the W300B, so let's wait for your next follow-up video...
I think they may have installed the 2 silicon diodes effectively in series with each rectifier to isolate the rectifiers from each other, in case one had a higher o/p voltage than the other. That 100uF filter cap may be ok, since you said the current rectifier tubes can handle up to 47uF, & the 2 rectifier tubes are basically in parallel. I'm no expert, & you've obviously had way more experience than me, but that's just my best guess. As you say, it can't be too great having real thin wires carrying high current filament power!
Not sure, but these are known for the rectifier tubes arcing out and is the reason they retrofitted them with that delay board, and that large first cap is the likely reason. Also I said >some< rectifier tubes can handle a max of 47uf, many 274 tubes say their max is 4uf. Like I said, I will do a video soon on why it's more than just the inrush current that makes a large first cap a problem. I've also never seen a need to isolate the sections of a rectifier tube from each other and this is no different. I think they added them to try to keep these from arcing out on start up, same with those 10 ohm resistors.
@@SkunkieDesignsElectronics In that case, it must be the only other possibility: Having some of the sag of tube rectifiers, plus the PIV of silicon diodes, with almost the same voltage drop.
I imagine there should be quite a high voltage drop across the tube rectifiers - if you were to bridge the tubes and only use the solid state diodes wouldn't the line voltage go up quite a bit?
The B+ voltage in the amp would go up, likely about 30-35V. Changes would be need to be made to compensate for this. I never meant to suggest anyone should do that!
Any idea when this unit was built and shipped? Mine was made just after the most recent Chinese New Year recently. Mine uses 5U4G rectifier tubes. I replaced the 6sN7’s with PSvane-UK models. Those improved the midrange clarity.
I bought my R300 end of February this year from China HiFi. It looks totally different. No 10Ohm resistors, only one diode, no delay board, different PS caps board. And it was delivered with 274Bs (only option at this time)….
It just came a couple of weeks ago from China. What I found is what is supposedly their latest revision, the model with the high voltage delay relay board.
@@thomasfi1275 Sad to hear that. My experience wasn’t like that at all. I ordered in early December thinking my item was in stock and I was told almost immediately that wasn’t the case and apologized and explained the factory was shut down for the Chinese New Year and they gave what they thought when my R300 was going to be built and shipped. It arrived two weeks earlier than expected. When I had a problem with the battery installation for the remote they responded quickly with a TH-cam video link showing me how to resolve the problem.
100 MFD condenser needs to be a 47 MFD bin the diodes bin the 10 ohm resistors add CL80 in series with the hot side of the mains the 330 MFD use a 100 MFD as the current draw on switch on would be better the choke needs to be 5 H 200 MA for better regulation and smoothing etc
Seen also on some amplifiers ...........where the rectifier or rectifiers.....are BYPASSED by diodes ..hahahaha , commercial illusion to sell amplifiers with the looks of using rectifiers.
I've listened hard but I still can't hear the sound of DC. Good DC is quiet. Bad DC hums. Valves or no valves, if you hear a difference, then your power supply was inadequate
Not sure I would buy one knowing it needs this work done right now. I promised the owner I would see what I could do to resolve the problems and it may not be as bad as I initially thought. If fixing the power supply fixes the performance issues, maybe it's worth it, especially then if Wilsenton listens and updates then with a proper fix for this issue.
Stephe, great work and my thanx🙏🏻👍🏻👏🏻 It looks like that there are different power supplies out there. Some hasn’t these delay board, has no resistors, has only one diode🫣
Thanks for sharing your stellar work here. I can tell as I am an electronics engineer, with experience working on tube amps for satellite uplinks. Some of them at 1500w at 14Ghz. Fridge sized. Lately I have also DIY'ed a few tube guitar amps (mostly 50's fender clones, but modded to be a bit less hummy) and also made a clone of a "cracking" headphone amp that turned out very well. Following your channel as I am looking into diy'ing a power amp, perhaps a 300B one... Keep up the great work!
I own this amp for last 5 months. It only played for 3 weeks. I have received 3 sets of tubes from China Audio so far. All of them died.The last set is 5U4GB EH tubes (made in Russia). I gave up and connected back my DIY Aleph J (FirstWatt clones). I really hope you will make this amp to be stable and play again. Good luck and thanks for your awesome work.
Oh I can absolutely make this power supply stable and reliable. :)
Wow, that’s eye-opening on what they did with the rectifier circuit. Also real clear great explanation on the rectifier circuit.
I had just bought the R300 and still waiting on its arrival. Then I found your recent videos. LOL. You've got me holding my breath and on the edge of my seat. I've been wanting my own 300B amp for years. I've got a modest budget for stereo gear. I still have hopes that this amp provide a good starting point that will deliver that 300B sound. I love modding my equipment so I'll be watching closely and probably following along. Thanks for tearing into this one.
Wow this was cool. Its like the original rectifiers were damn near just for show. Im sure your revised power supply will yield great results. It will at least be more stable and reliable. They seem to over complicate things and maybe dont quite get how to design a circuit right. Im really interested in seeing where this ends up. Great job as always, thanks.
I agree, they're obsessed with appearance. Plug-in solid state rectifiers with thermistors would fix it quickly but if I'm buying a tube amp, I want tube rectifiers.
Your work is truly remarkable ! But I'm starting to cringe at the prospect of changes that are likely to be too big for my taste ... But I'm going to hang in there and try to understand as best I can and judge whether it's all within my capabilities or not. Thank you for such an enlightening analysis of how to make this machine better :)
I'm trying to keep them as minimal as possible!
@@SkunkieDesignsElectronics Merci :)
Wow!!! What a mess, gotta wonder how they design this stuff. Great work Steph. You can only improve this.
Super interesting! Eager to see what this mod does to signal respons. Do you think that the global feedback implementation in this amp design may be contributing to the weird square wave response?
Yes and I wonder if the feedback was used to reduce the PS noise, which then created other problems?
@@SkunkieDesignsElectronics Ahaa.., lets see if you get any opportunity to check that out, thanks!
Thanks for the awesome information, always posting great videos.
Thanks for watching!
I'm not familiar with the 274 rectifier so I looked it up and i agree they are badly abusing it and that the first smoothing cap is probably killing the 274's.. It was chosen for it's looks and little else.The 5AR4 tube solves the slow start problem and is a pretty rugged tube if you follow the rules by reducing that first smoothing cap..
This is one of the reasons that I always ask individuals who want to use Emission Labs 274A/B rectifier tubes if they know the value of the amplifiers first capacitor. Using more than a 4uF cap as the first cap with a 274 is a big no no.
This one is 25X that!
@@SkunkieDesignsElectronics and of course the wrong value capacitors as you've correctly pointed out.
The mysterious diode is essentially a support for the rectifier tube to prevent the entire current from flowing through the tube during power-on. The large charging capacitance demands a very high current at power-on. It should be considered to slow it down slightly with a small capacitance. Otherwise, it does not affect the sound......thx for the vid
But the entire current does flow through the tube for it to be able to make it to that diode. They are in series. Series diodes improve their voltage handling, parallel ones increase their current. And large first caps impact a tube rectifier in more ways than just inrush current.
@@SkunkieDesignsElectronics You absolut right!.....thats my fault, because I saw the video in 480p mode.Thx for your comment.....or I would never know I need glasses.
Looking forward to you fix. Keep the videos going🍿in hand
Seen it before ............rectifier +diode ............questions ? YES !..............but one fact remains that the rectifier has a galvanic separation and an internal impedance , both conditione nevertheless the sound .
Normaly a delay that applies the high voltage when the heaters are fully warmed up should not switch the HV to the circuit that way , only so with solid state diodes ........but with DIRECT HEATED rectifiers the filaments of rectifier tubes must be switched on/off !
NO worries with indirect rectifiers as they have a delay of themself ...
Another mistake is also seen on commercial tube amplifiers is ....
1) The warm up period only switches the inputs/outputs ............
2) The HV must be shut down before the heaters of the tubes are shut down and the power supply capacitors must be drained before switching off the heaters .......
Both cases/design errors do not protect against stripping of the cathodes of your precious tubes ......
Correct start up and correct shut down expands the usefull life of tubes by several times .
20 000 H on a 211/845 and almost 100 000 H on a 12AX7 etc are not uncommon when used respecting this or never shut down the amp ( BBC policy= never shut down their tube amplifiers ) .............only with nos tubes !
For example WE 408a and other types ............12 years continous use on test bank ..........Still within specification ! equals 24 hours times 352 days times 12 years ........calculate the Ihours under controled conditions within normal operation conditions .....
In 1924 ............A standard 101D /F has a lifespan of 40 000 /60 000 hours ..........( thelephone repeater tubes )
In reality , commercial practice ,manufacturers need selling tubes as much as they can at roaring prices , so WHY protect tubes .............?
Now I am curious watching the next part of the video to see what you find out about the power supply ..............nothing asthonish me anymore today with the boom of many but not all badly designed asian tube amplifiers .
Thank you the upload and sharing .
@skunkiedesignselectronics - Thank you for your detailed reviews. I find them helpful and informative. What is your take on the headphone output for this unit? Is it similar to Wilsenton R8 or better?
Looks like the same mess.
I could be wrong but like to have a shot. It looks that the tubes are in parallel to up the current available, and the diodes are blocking diodes. However, the new power supply design will work just fine.
the diode i believe makes it kind of a hybrid tube and diode rectifiying. increases supply voltage because you cant really parallel two tube rects to make it a bridge
Interesting Stephe! I might be a good plan to flush mount the socket for the future 5AR4's, as they may look weird in the current low position. Also, would it be beneficial to upgrade the existing choke to a better (or similar) quality as the new Hammond choke?
It probably would, I have a spare 194G 3.5H choke I may replace the current one with.
@@SkunkieDesignsElectronics A shame the two rectifier tubes are in parallel, it would be nice to make a dual rail PSU. Looking at the schematics, that may be challenging but it would be a chance to get rid of the crazy big 330uf cap 😛
Trying to find room for 4 chokes just isn't going to happen, especially with the input relay board and that other PS board for the bias voltage.
Thank you so much for this much awaited video...I've been thinking of getting the W300B amp, but I I have to admit that I felt a bit intimidated on the potentially necessary modifications, I am new to this, but I just recently recapped a Sansui vintage receiver, and the end result was favorable, Now,, I'm working on a vintage Marantz tuner. I really hope to be able to make this modification, if and when I get the W300B, so let's wait for your next follow-up video...
Glad it was helpful!
CLCLCL ....33µF/100µF/330µF is correct way of designing the values of ps caps in this case !
4:18 Maybe a security measure to make sure if the tube fails which it will not conduct AC and fry and smoke?...
I think they may have installed the 2 silicon diodes effectively in series with each rectifier to isolate the rectifiers from each other, in case one had a higher o/p voltage than the other.
That 100uF filter cap may be ok, since you said the current rectifier tubes can handle up to 47uF, & the 2 rectifier tubes are basically in parallel.
I'm no expert, & you've obviously had way more experience than me, but that's just my best guess.
As you say, it can't be too great having real thin wires carrying high current filament power!
Not sure, but these are known for the rectifier tubes arcing out and is the reason they retrofitted them with that delay board, and that large first cap is the likely reason. Also I said >some< rectifier tubes can handle a max of 47uf, many 274 tubes say their max is 4uf.
Like I said, I will do a video soon on why it's more than just the inrush current that makes a large first cap a problem.
I've also never seen a need to isolate the sections of a rectifier tube from each other and this is no different. I think they added them to try to keep these from arcing out on start up, same with those 10 ohm resistors.
Could be an implementation of the yellow sheet mod.
Nope, this is different. This one is in series on the DC side. after the tube.
@@SkunkieDesignsElectronics In that case, it must be the only other possibility: Having some of the sag of tube rectifiers, plus the PIV of silicon diodes, with almost the same voltage drop.
When I saw two rectifier tubes, I tought one for each channel. Why would they run two of them in parralell?
Great video !!
I imagine there should be quite a high voltage drop across the tube rectifiers - if you were to bridge the tubes and only use the solid state diodes wouldn't the line voltage go up quite a bit?
The B+ voltage in the amp would go up, likely about 30-35V. Changes would be need to be made to compensate for this. I never meant to suggest anyone should do that!
Did they see which rectifier tubes they could get the cheapest then wait for the product returns to work around the flaws?
Part of this could be aesthetics + internet hype over these 274B tubes.
@@SkunkieDesignsElectronics Here's my 2nd vote for hype.
Any idea when this unit was built and shipped? Mine was made just after the most recent Chinese New Year recently. Mine uses 5U4G rectifier tubes. I replaced the 6sN7’s with PSvane-UK models. Those improved the midrange clarity.
I bought my R300 end of February this year from China HiFi. It looks totally different. No 10Ohm resistors, only one diode, no delay board, different PS caps board. And it was delivered with 274Bs (only option at this time)….
It just came a couple of weeks ago from China. What I found is what is supposedly their latest revision, the model with the high voltage delay relay board.
@@thomasfi1275 That’s about the time I received mine, straight from ChinaHiFi. I had great communication with them.
@@Photoboy1948I have bad experiences with communication with China Hifi. They reply vague and then stopped generally.
@@thomasfi1275 Sad to hear that. My experience wasn’t like that at all. I ordered in early December thinking my item was in stock and I was told almost immediately that wasn’t the case and apologized and explained the factory was shut down for the Chinese New Year and they gave what they thought when my R300 was going to be built and shipped. It arrived two weeks earlier than expected. When I had a problem with the battery installation for the remote they responded quickly with a TH-cam video link showing me how to resolve the problem.
Can you provide a parts list of the power supply mod?
When I get done with it I will lol
Thank you for a great analysis. Your brain must hurt!
It is amazing that a largish company can make such errors. You might obtain a consultancy
Stay tuned :)
100
MFD condenser needs to be a 47 MFD bin the diodes bin the 10 ohm resistors add CL80 in series with the hot side of the mains the 330 MFD use a 100 MFD as the current draw on switch on would be better the choke needs to be 5 H 200 MA for better regulation and smoothing etc
I don't think a 5H 200ma choke will fit inside this amp. I actually prefer a 33uf first cap to give the rectifier tubes some headroom.
@@SkunkieDesignsElectronics find new spot
1.5H + 3.5H is 5H.
@@SkunkieDesignsElectronics just use 5 H 200 MA the PSU in that unit is very crappy rip it all out start again easy job
Why don't parallel the 5AR4
Because it's not needed. Why throw extra tubes in an amp for no reason?
Seen also on some amplifiers ...........where the rectifier or rectifiers.....are BYPASSED by diodes ..hahahaha , commercial illusion to sell amplifiers with the looks of using rectifiers.
I've listened hard but I still can't hear the sound of DC. Good DC is quiet. Bad DC hums. Valves or no valves, if you hear a difference, then your power supply was inadequate
That's been my position: if you can hear a difference when you change a rectifier tube, at least for HiFi use, the power supply was designed wrong.
100 % bin the diode, amazing how designers use diodes on valve rectifiers. bin the delay board to its catawampus garbage
I thought you said the r300 was no bueno and not worth the time.
Not sure I would buy one knowing it needs this work done right now. I promised the owner I would see what I could do to resolve the problems and it may not be as bad as I initially thought. If fixing the power supply fixes the performance issues, maybe it's worth it, especially then if Wilsenton listens and updates then with a proper fix for this issue.
@@SkunkieDesignsElectronics I really enjoy your videos, thank you for making them
Stephe, great work and my thanx🙏🏻👍🏻👏🏻
It looks like that there are different power supplies out there. Some hasn’t these delay board, has no resistors, has only one diode🫣
I do think there have been variations of these amps. So you know where the one diode was placed?
@@SkunkieDesignsElectronicsdiode is at the same place as yours. But only at one rectifier tube socket ….???
OK I saw it, and yeah it combines the two rectifiers and then has a diode on the output.
At my R300 this cap labeled 220uF🫣 AND was delivered with Willsenton branded 274Bs🤬
Yeah, I'm not sure what is going on with the earlier version of this amp.
@@SkunkieDesignsElectronicsbought my R300 new this year in March from China Hifi….
@@thomasfi1275 I have two, recently purchased, long story short. One of them matches the example on Stephe's video.