I'll know tomorrow.
Willsenton R300B SE Integrated Amp
- Thread starter CohibaJoe
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How odd a company trying to censor the truth.
I need to clarify, they didn't directly say "Please remove your video", but they were clearly very upset seeing my videos exposing these issues with their products. I think part of my confusion with their email may be language and/or culturally based? And clearly they can't censor what I publish. Since then, I have been in further contact with them, and they do seem to be genuinely concerned with what I found, with both of their amps I have reviewed, and want to resolve these issues in future products/ASAP.
They did supply me with a schematic for the R300, that at this point they asked me not to share and I am going to honor their request. I do plan to dive into this stuff in a future video soon, and feel I can share the power supply details in the as built amp.
I can say: the first cap after the rectifier is a 100uf (too high) and the rectifier tubes are wired as full wave, with the plates of each tube tied together in parallel. They have added a delay relay board to later production amps, which postpones the high voltage AC being applied to the rectifier tubes until they (and other tubes) have warmed up. I'd rather see slow warm up tubes like a 5AR4, with a much smaller first cap and then a 4-5H choke, followed by the 100uf and then the rest of the current power supply (100uf/choke/330uf). It would end up with much cleaner DC as well. That or drop in some SS rectifiers, but that doesn't clean up the DC anymore than it currently is, and may require a bias adjustment.
They did supply me with a schematic for the R300, that at this point they asked me not to share and I am going to honor their request. I do plan to dive into this stuff in a future video soon, and feel I can share the power supply details in the as built amp.
I can say: the first cap after the rectifier is a 100uf (too high) and the rectifier tubes are wired as full wave, with the plates of each tube tied together in parallel. They have added a delay relay board to later production amps, which postpones the high voltage AC being applied to the rectifier tubes until they (and other tubes) have warmed up. I'd rather see slow warm up tubes like a 5AR4, with a much smaller first cap and then a 4-5H choke, followed by the 100uf and then the rest of the current power supply (100uf/choke/330uf). It would end up with much cleaner DC as well. That or drop in some SS rectifiers, but that doesn't clean up the DC anymore than it currently is, and may require a bias adjustment.
With respect to the need for slow start, 5U4 and other direct heated rectifier tubes certainly make up the vast majority of tube rectifiers used in the tube era.
I'm not sure this is actually a "soft start" as it just lets the heaters get a head start and then throws the HV at them.
But I'm pretty sure they didn't use a 100uf cap right after them either.
The 5U4G is limited to 4uf, the GB is 40uf. At least with a 5AR4 the voltage is ramped in slowly enough where the inrush current is minimized. But you still can't just throw a huge first cap behind them for the other reasons.
True, and I've never understood the benefit of pushing it, but there are vintage designs that go beyond the limits. My Radio Craftsman Model 2s have a 60 UF immediately after a 5Y3. Still, it makes much more sense to have a 40uF in the amp in question.But I'm pretty sure they didn't use a 100uf cap right after them either.
FlaCharlie
Super Member
Just to clarify something that some owners of these amps may not be aware of . . . you are talking about the Sophia Electric "Aqua" version of the 274B only.
Boutique tube manufacturers will sometimes come out with a new tube and, even though the specs are not the same as the original tube it's based on, they will use the same tube number for marketing purposes.
The "Aqua" versions of their "274B" allow the use of a 47uf first cap but their specs are not the same as other 274Bs, including their "regular" 274B, which handles much less current and requires a smaller cap.
They are also very expensive tubes. Their cheapest version of the "Aqua" is $200 each with a 30 day warranty or $240 each with a 1 year warranty. So you're essentially buying an extended warranty for $40.
Their newer "Aqua II 274B" sells for $250 each with a 30 day warranty or $300 each with a 1 year warranty. So that's an extra $50 for an extended warranty.
Of course the R300 uses two rectifiers. So only R300 owners who are interested in spending $400 to $600 on rectifier tubes should consider these.
For those who are using normal 274B rectifiers, including other expensive "boutique" brands, a 47uf first cap is simply too large. See my post #45 earlier in the thread. The data sheet for a traditional 274B indicates a max of 4uf. Note that EML, another boutique manufacturer, is very strict about this, saying that their 274B should never use anything larger than 4uf under any circumstances.
In my earlier post I (perhaps mistakenly) claimed that the 5U4G also had a cap limit of 4uf. I say "perhaps" because the data sheets don't always agree and are bit confusing. I saw one that lists 40uf and another that lists 32uf, yet the graphs showing cap input characteristics show 4uf. So
The common, tough, 5U4GB can certainly be used with a 47uf without having to add the "band aid" fix that Willsenton is offering as a solution to their engineering problem.
It's likely that even a single 5U4GB would work fine, depending on how the PS is wired.
I'm not an expert in rectifier tubes but suspect that the 2x the maximum value of the first cap might be allowable when two tubes are used instead of one because the pair should be able to handle 2x the current draw. Perhaps someone with more technical expertise can answer this definitively.
If so, even the stock 100uf first cap should be OK if you're 5U4GBs, the 274B "Aqua", and perhaps (??) even the 5U4G. But NOT if you're using normal 274Bs.
This can and should be confirmed by the graphs in the data sheets. The amp must pass all 3 tests and actual measurements from the amp must be used.
The boutique tube manufacturers all claim that their expensive rectifiers are sonically superior, of course. You might want to read the recent / current thread about rectifier tube sonics before you decide to spend that kind of money.
Rectifier tube sonic differences?
This is something that baffles me and I'm trying to understand. How can a different brand of rectifier tube impact the sound of an amp, especially a single ended one? I could possibly see in a push pull design, if one tube vs another creates more or less sag, but that's not really a thing in an...
www.audiokarma.org
5U4GBs are plentiful and cheap. The big dealer near me (Radio Electric Supply) lists them for $15 and a dealer in Orlando (Vacuum Tubes Inc) lists them for $20. These are NOS American tubes which have earned a reputation for being tough as nails. No extended warranty necessary. Almost all of the used 5U4GBs I've tested still test as new and most of them probably spent their lives in old TV sets and have a lot of hours on them.
I am waiting until Stephe reviews the schematics for a complete picture of what is going on. Here we should find out what values to add or remove, wire cleanups, choke replacement, etc. I have not had any red plating as my 2nd R300 parts upgraded has 350+hrs..
That 0.33uf cap across that power supply electrolytic doesn't need to be a high end cap. I'm not sure those 0.22 caps are going to stay that value. I'm pretty sure when I am finished modding the power supply, you won't hear any difference changing the rectifier tubes, you shouldn't on an SE amp. If you can "hear the rectifier", there is something wrong.
FlaCharlie
Super Member
My speculation is based on the fact that the maximum cap value shown in a rectifier's data sheet is based on its use in a circuit that operates the tube at it's maximum voltage and current output.
A larger cap can be used if the rectifier is operating at less than its maximum voltage and/or current. The charts I keep mentioning allow you to determine how much larger the cap can be under those less stressful conditions.
So IF dual rectifiers are capable of supplying more current, I'm speculating that this would allow the first cap to be larger. Speculating. Hopefully someone with more knowledge about dual rectifiers will clarify.
I would suggest that you be patient and see what Stephe comes up with before you make any changes at all. The only thing I would suggest you do for now is not run a "regular" 274B. And if you have those super expensive boutique "Aqua" 274Bs, you might also want to run something else unless you consider the cost to replace them to be chump change.
As I said in the thread that I linked, I've never heard any difference between different rectifier tubes myself. I suspect any audible difference would be due to the fact that different types have different voltage drops. If the B+ voltage is the same I doubt you would hear any difference and this is especially true for a SE amp because all SE amps run in Class A, which means they operate at essentially constant current. That's the basis for Stephe's comment - that if you can "hear the rectifier" in a SE amp there is something wrong.
If I owned one of these amps I'd just use a pair of good old American 5U4GBs. The total cost of the pair would be about the same as paying for an extended warranty on a single "Aqua" 274B.
Like Stephe, I prefer to use indirectly heated rectifiers that slowly ramp up the voltage at startup. When using directly heated rectifiers I like to add a thermistor. This slows the inrush current a bit, but it's nowhere near the slow start provided by an indirectly heated rectifier.
While those are my preferences, I'm not convinced that it's all that critical. I have vintage amps that run directly heated rectifiers without a thermistor and there don't seem to be any issues as a result.
Running too large a cap does create issues though. Be patient. Give her a chance to come up with a solution.
So all issues you and customers did found at the Willsenton R300 and R8 until today are true and do also concern the manufacturer.
I am shocked
I think originally they may have intended to use 5AR4 rectifiers. Part of this is customers want these fancy bottle rectifier tubes for aesthetic reasons, like these 274B tubes match the shape of the 300B tubes. Straight bottle tubes are boring looking.For months now I see changes and confusions about the rectifier tubes of the R300.
They sold the R300 with 5U4Gs, then with 274Bs, then with 5U4GBs. And with/without this delay board…
Asking the dealer china hifi never gave me sufficiently answers…
design over function!?
…but the 5AR4 do have low voltage drop...could this cause any “more“ issues?
R300 manual listed different tubes
If I owned one of these, especially without that delay board, I would 100% be installing a pair of 5AR4 tubes, especially given the manual shows them a direct swap. Do NOT use JJ brand 5AR4 tubes. Gold lion, TAD and Sovteck all work well for modern 5AR4 tubes. Several benefits, slow voltage ramp up, they can deal with larger capacitors easier, the heaters use less current, so the power transformer will run cooler + the tube generate less heat than those 3A each 5U4G/GB type tubes do. I plan to try these in the one I have, measure the voltage difference and see where the bias is after the change.design over function!?
…but the 5AR4 do have low voltage drop...could this cause any “more“ issues?
R300 manual listed different tubes
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