Willsenton's R8 KT88/EL34 Tube Amplifier

Jon S said:
On a side note, i tried getting the 0.1uF 500v K42Y-2 capacitors for the modifications done on the StereoNet site. These are Russian caps and are now unobtanium. The only sellers are either in Russia or Ukraine. I have recently ordered some tubes from Ukraine and it is taking a long time to ship (expect 6-8 weeks) because of the war. I tried to find other similar caps and they are ridiculously expensive.
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Are the caps in the amp 0.1 uf? The only schematic I've seen shows them as 0.22 uf. If the 500v rating is hard to find, you can always use ones that have a higher voltage rating, such as 630v.

The Russian caps are nice. I really like the K40Y-9 version. I've always gotten them from Ukrainian and other E. European sellers and I've never had a problem.
 
The caps are four 0.22uf and a pair of 0.33uf. Changing them to 0.1uf is gonna affect the frequency response. And the voltages where these caps are located are operating at much lower voltages, I'll have to measure to see what this is.
 
Jon S said:
OOC, why is not recommended to power on for five minutes after shut off. Also, what happens if you power on with no speakers connected?
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Worth repeating ... tube amps need to discharge the storage caps on shut down. Hot loading them right away can make for all sorts of interesting results, none of them good.

*Also a big fan of using a "non-latching" GFCI adapter like those used in the construction trade. ANY little power blip (lightning, grid problems, etc) trips the adapter and requires a manual reset, preventing hot loads spewing all over your sensitive bits (probably a better way to put that) as long as you wait a few minutes. Cheap and effective protection.

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PS - sounds like you got a good one, but I tend to shy away from pretty lil box transformers, as you really don't know what you're getting. Pop the top off the can and find something like this rattling around inside? No thanx, eh.

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Oh. Some amps can handle idling without speakers semi-gracefully, but why chance it?
 
Sorry. I meant the 0.1uf caps used to bypass the large 450V 330uf filter caps as well as the 6SL7... More on this here.

On a side note, a good tube combination for me right now is the Electro-Harmonix 6CA7EH, the stock Willsenton 6SN7 and a pair of Foton 6N8S (6SL7). I tried it with a set of GE 6SN7-GTB and it sounded too warm and smooth, the highs were gone. Putting back the stock Willsenton 6SN7 (which is too bright and harsh on its own) balanced out the Foton 6N8S which is a pretty warm sounding tube. The 6CA7 has a bit more bass from other tubes but it sounds a bit bloated.
 
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Jon S said:
Sorry. I meant the 0.1uf caps used to bypass the large 450V 330uf filter caps as well as the 6SL7... More on this here.

On a side note, a good tube combination for me right now is the Electro-Harmonix 6CA7EH, the stock Willsenton 6SN7 and a pair of Foton 6N8S (6SL7). I tried it with a set of GE 6SN7-GTB and it sounded too warm and smooth, the highs were gone. Putting back the stock Willsenton 6SN7 (which is too bright and harsh on its own) balanced out the Foton 6N8S which is a pretty warm sounding tube. The 6CA7 has a bit more bass from other tubes but it sounds a bit bloated.
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I read what you posted. Bypassing the large filter/storage cap in the power supply isn't likely to do much and given those caps needs to be replaced due to being underrated, just get some good quality ones.

As far as his other mod, why would you place a film cap between the plate of the cathode follower section of the amplification tube and ground?

When I read things like " I now sense holographic imaging of the music" and "satin paint texture turned to glossy"...
 
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Stephe, I have couple of questions for you.

The volume control on the R8 is too aggressive. With my 86dB/watt Polk Lsi15's I never go past the 9 o'clock position as it gets too loud. That restricts my volume control to the 7 o'clock to 9 o'clock range. Is there a way to change it so that the sweet spot for the control is about 12 o'clock?

Secondly, it appears that a common issue with the volume control has a bit of static when adjusting the volume on the right channel. Is there a way to spray a contact cleaner like DeOxit into the volume pot to fix this issue? IIRC, most pots have an opening for such a procedure. Thanks in advance.
 
Definitely ordering one of these! Thanks!

sKiZo said:
Worth repeating ... tube amps need to discharge the storage caps on shut down. Hot loading them right away can make for all sorts of interesting results, none of them good.

*Also a big fan of using a "non-latching" GFCI adapter like those used in the construction trade. ANY little power blip (lightning, grid problems, etc) trips the adapter and requires a manual reset, preventing hot loads spewing all over your sensitive bits (probably a better way to put that) as long as you wait a few minutes. Cheap and effective protection.

41if9a4qmhL._AC_.jpg
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ive so enjoyed this discussion. beon very curious about the wilsenton, i neem watching/listening to skujysnvids about it as well.

the current production russian tung sol 6SL7 are quite good. i use em in a tavish phono. currently usin some microphonic, stubby lil RCA clearglass.
 
I did a few of the mods listed in the Stereonet forum.
1. The GNFB mode, replace the two 33k-ohm resistor with a 5.6k-ohm
2. Insert a 0.1uf 600v cap across the two power caps
3. Insert a 0.1uf 600V cap from pin 5 of the 6SL7 sockets to the ground buss
4. Replace the four Willsenton 0.22 caps with ClarityCaps

It's too early to see what differences the mods made, but the biggest is the GNFB. It changes the operation of the volume control to a more usable range. Before, I could only adjust the volume to 9 o'clock but now that same volume level is reached when the control is at 12 o'clock. Initially i could not hear any sonic differences but as I put on the hours, there is a subtle increase in the soundstage focus and a bit in depth. Classical music sounds a bit more realistic with a you are there feeling. I don't feel the same performance with pop/rock music other than a sharper focus. I will update as the hours are increased.

One more note. The R8 originally was supplied with a pair of 30mm diameter 330uf 450v filter caps. I was surprised that my R8 had the 35mm version of the 330uf 450V caps. I had already bought the 30mm caps and now have to buy the larger ones. In a way it was a good change. I could only find 500V caps in the 30mm size. I now have the option of buying safer 550v caps.
 
So far, the modifications seem to be subtle in most cases. When listening to pop or vocals, the differences are subtle. There is a smidgen more clarity, detail and focus. Soundstage seems about the same except to when listening to classical music. When listening to far-miked classical music (e.g. Deutsch Grammophone) the image is very wide and wall-filling with a bit more depth. If the music was recorded with near microphones, the differences are more subtle.
 
I just installed my two 330uf 550v capacitors. I originally ordered 30mm diameter caps but when I opened up my R8, the caps were 35mm in size so i had to order another pair. I also installed a new choke as recommended by Stephe, the Hammond 194G 250ma both from Mouser. Unlike Stephe's case, the new choke was a drop-in replacement, I did not have to adjust the bolt holes in my R8. It seems that the R8s are still going through modifications in production and Steph's R8 is not a current model.
 
StepheK said:
I read what you posted. Bypassing the large filter/storage cap in the power supply isn't likely to do much and given those caps needs to be replaced due to being underrated, just get some good quality ones.

As far as his other mod, why would you place a film cap between the plate of the cathode follower section of the amplification tube and ground?

When I read things like " I now sense holographic imaging of the music" and "satin paint texture turned to glossy"...
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Maybe it's just for local supply bypass.
 
Changing to that much global feedback without analysis is not optimal. You may want to shoot some square waves through the amp to see how things look on a resistive load. Then add some capacitance to the load and retest. Finally just load the amp purely capacitive and see how stable it is. I'm going to bet with adding that much feedback the amp is going to be marginally stable or at best conditionally stable.

There is a reason we add lead/lag compensation networks to feedback amplifiers.
 
I just got my supposedly NOS MELZ 6N9S (aka 6SL7) tubes that I ordered from Ukraine in December. On close inspection, the bases looked grungy around the center guide pin and the pins themselves looked pretty bad themselves. At least the tube was affixed firmly in the metal bases (I bought a quad of supposedly NOS NEVZ 6SN7s earlier and all of them were loose, one tube was DOA).

One tube base had a slight hairline fracture. The tubes themselves looked clean and the bases themselves looked okay.

After cleaning all the pins with steel wool and a brass brush I sprayed Caig's DeOxit and inserted them into my R8. I can see what the fuss is all about with MELZ tubes. There was more clarity with a bit wider image than my vintage Sylvania 6SL7-WGT Gold and my GE 6SL7GTB. My reissued Tung-Sol 6SL7-GTB just sounded "hard" with a smaller image compared to the MELZ. I just hope that the MELZ tubes will last a while. I am definitely will be on the lookout for more MELZ tubes in the future. Seeing how rarely they pop up on eBay it will probably be a while.
 
Jon S said:
I recently watched some YouTube videos on the Willsenton R8 KT88/EL34 integrated tube amplifier and decided to purchase one. Amazon sells it for $1500 but you can buy it directly from China-hifi-audio for about $900 plus shipping (in my case, it was about $330 to Hawaii). Since Amazon was out of stock, I chanced it and purchased it from China-hifi-audio, saving almost $300. I was also considering the R800i but for some reason they could not ship it to Hawaii because of its 100+ lb weight.

Here are the specs:
Willsenton R8 Class AB integrated tube amplifier
  • Power: 45wpc in Ultralinear mode, 25wpc in Triode mode (KT88 tubes)
    40wpc in Ultralinear mode, 25wpc in Triode mode (EL34 tubes)
  • Weight: 65 lbs shipped, 57 lbs for amp only
  • Frequency effect: 10Hz 40kHz (+/-0.5db)
  • Total harmonic distortion: 1% (1kHz)
  • Signal to noise ratio: 91dB
  • Input sensitivity: 380mv (when Integrated amp input) 820mv (when pure power amp input)
  • Input impedance: 100KΩ
  • Output impedance: 4Ω, 8Ω
  • Power supply voltage: 230V ± 5% (50Hz/60Hz) ~ 115V ± 5% (50Hz/60Hz)
  • Machine volume (400*200*390) (W*H*D) mm
  • Use vacuum tube: 6SN7*3.6SL7*2.KT88*4/6550EH*4/EL34*4
  • Power consumption: 310W

I received the amplifier in a week (surprisingly, it was shipped from California, I think it was the exact same address as the Amazon seller). The amplifier was extremely well packed, double-boxed as well with additional foam around the tube section to prevent it from loosening and most cases of shock. One thing to notice is the amp is extremely heavy, weighing about 30 kilos or 65 lbs. Unpacked, the amp weighs about 57 lbs.

I ordered the silver/black model with the Willsenton branded KT88 tubes and was impressed by the quality of construction. The amp can be ordered with the Willsenton branded EL34 tubes as well from China-hifi-audio for $100 less but Amazon only sells the KT88 model. The amp has three huge power transformers in the back. It uses four KT88/EL34 tubes for power, and three 6SN7 and two 6SL7 tubes. The front panel has a power control, LED indicators for CD, AUX 1, AUX 2, Pre-in and TR/UL (Triode/Translinear) mode. In the center is a bias meter. To right of it is the TR/UL selector, input selector and volume control. The rear panel has the CD/AUX 1/AUX 2/PRE-IN inputs. There are separate connectors for 4-ohm and 8-ohm speakers, a tube selector switch for KT88/EL34 tubes and the IEC power connector.

Be careful when setting up the system. I read that tube amps should not be powered up without the speakers being connected. How true that is, I don't know. The amp comes with a metal remote control that uses two AA batteries. You have to unscrew the bottom of the remote and remove the battery holder. The remote controls the amp mode, volume and input selector.

Without even breaking in the tubes, there is a noticeable sonic improvement from my prior solid state amps (I was using a SoundArtist SA200ia amplifier (rated 150wpc @ 8ohms/200wpc @ 4ohms) and a vintage Acurus DIA-100 integrated amp, speakers used was a pair of Polk LSi15 and Magnepan 1.6QR planar speakers). Instruments and vocals were a lot smoother with less harshness. Imaging was slightly improved with a bit of depth and a tad more localization of sources, but not the 3D holographic effect some were mentioning. Right now, I have about 30 hours on the tubes and it seems to be improving a bit. Considering it defaults to only 25wpc in triode mode, I was surprised to note that the amp had no issues driving the Polks or the difficult Magnepans. Magnepans are well-known as difficult to drive speakers, but the Willsenton exceeded my expectations. Tube amp wattage always are difficult to asses, as a tube watt sounds louder than a solid-state watt, since tubes can supply more current compared to a similarly powered SS amp and Magnepans love current... I never had the volume past the 10 o'clock position as the music would be too loud for my taste (I only play music at moderately loud volumes). Female vocals are fantastic on this amp. They sound so smooth and natural. Jazz music is extremely revealing in clarity. Rock music is so-so, classical music is expansive but can be a bit compressed during peak passages, probably due to the low power output.

Some things to note, the amp was powers on with the CD input selected and operating in the triode mode which is limited to 25wpc. Note that there is a 30 second mute delay after the unit is powered on. The remote operates with a slight annoyance. When adjusting the volume, the remote adjusts it in too large of an increment. The music may be a bit too soft and a tap on the remote will make it a bit too loud. You can see the volume knob moving quite a bit in use. The volume attenuator itself may be a problem. When listening to music, I never had the volume knob past its 9 o'clock position. Like most volume knobs, the range from off to 10 o'clock has a huge range in volume to cover.

The KT88/EL34 tubes need to be biased occasionally during its lifetime. Biasing the tubes is simple. Press the appropriate lever and adjust the bias pot until the meter is centered. All of the tubes were biased a bit hot out of the box and it were rectified. Checking the bias along the way did not see any changes. The other tubes are supposed to be self-adjusting.

Question is how long will the tubes last? From what I have read, they can last from 1,000 to 5,000 hours depending on how hard you drive them. Tubes are getting more expensive and as time goes by, I do not expect it to go down, especially since a lot of the tubes are sourced from Russia. I have seen tube prices jump 100% in the past year, and am looking at around $400-600 just for a set of four KT88s. I also noted that the manual states that after power off the amp, it should be powered back on for five minutes. I am trying to get some clarification on this puzzling note.

Am I glad I bought the Willsenton? It's not a resounding yes, more of a cautious yes. If the sound keeps improving, then my opinion will improve as well. I am planning to buy better tubes in the near future and hope they will make a bigger improvement in sound as other have mentioned, as I have read the stock tubes are just adequate. For me, this was a big investment, but it was time I entered the waters of tube amps. So many of my friends have gone that way and never looked back.

If you have any questions, post them here and i will be glad to answer them if I can.
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I have heard good things about these amps, but have never heard one. Steve Huff thinks highly of them:

https://www.stevehuffphoto.com/2020...ntegrated-tube-amplifier-is-a-no-brainer-buy/
 
I see some supposedly MELZ 6SL7 tubes with carbolite bases iso metal bases. How do these compare? Are they the real deal?
 
Let me get this straight. You increased the negative feedback, which the original value was 33k and you went to 5.6k? That's not a small change.

Did you measure the gain of the amplifier with the feedback disconnected then compare the gain with the 33k? Repeat for for 5.6k? Just trying to see exactly how much negative feedback you have going on.

Even if they had only -6db of negative feedback originally and you swapped the 33k for the 5.6k you may be around 20db or more. You seriously may want to consider seeing how stable your amp is before you burn up some speaker parts.

The more negative feedback you use the less changing tubes makes a difference. Once you get to -20db or more of negative feedback it's just going to be pointless to "tube roll". I always scratch my head a little when I see guys spending a lot of money trying different power tubes in a McIntosh. Their power stage is under nearly 100% feedback and operate at near unity gain. Any tube that's functional will sound the same in those amps. A good sign of solid engineering.
 
I will take your and Stephe's advice and revert the GNFB resistor back to its original value. I am one of those who just follow the general consensus and see what happens. I know some basic electricity but not enough to know these things which is a dangerous thing. people who think they know enough can be a dangerous and stupid lesson. Thanks.
 
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