I remember reading the Facebook R8 page.  It mentioned that the R8 choke was relabeled, not upgraded.  So it still had the same old 180 MA choke.  I use EL34s in my R8 so I should not have an  issue with the choke.  As a precaution I think I will get the 194G choke.  

1 hour ago, xinvisiblex said:

 

The amplifier has already been checked and fortunately only the choke is damaged. There were concerns that the output transformers were also damaged, but they are fine. When asked what caused the damage? I received the answer that the choke was too weak and was operating at the limit of its capabilities. But it was also mentioned that several 450V capacitors should be replaced with 500V, because they also work at the limit of their capabilities, and these 2x large, black filtering capacitors, because when the amplifier starts the voltage is close to 500V and again everything works at the limit of its capabilities, so it is necessary put 550/560V capacitors there. Fuses are also to be inserted after the choke and in the sensitive tube power circuits (whatever that means :7). Generally, I was told that these changes are very necessary, because if the voltage in the network suddenly jumps to 245V, there will be no breakdown (?), because the capacitors will have adequate reserve. Out of curiosity, I asked what the general opinion about the amplifier was? I received the answer that it was built quite ok. Nice appearance, good materials, very well fitted sheet metal, Nichicon capacitors, inserted fuse resistors, but they do not understand why several elements have too low values, instead of providing something with a larger margin. So, despite many changes introduced compared to the mk1, there is still something to improve. Maybe in the mk3 everything will finally be as it should be :7

Thank you for the update. Much apreciated.  In my R8 the original choke was replaced with Hammond 194 and it was the Hammond that got melt?!? Talking about luck .   I’m looking to replace with a larger toroidal choke transformer . 
 

glad to hear your R8 is up and running 

1 hour ago, jon96789 said:

I remember reading the Facebook R8 page.  It mentioned that the R8 choke was relabeled, not upgraded.  So it still had the same old 180 MA choke.  I use EL34s in my R8 so I should not have an  issue with the choke.  As a precaution I think I will get the 194G choke.  

 

I mentioned to them that the original version was 180ma. In the new version, the manufacturer supposedly gave 220ma, but whether they actually gave it or just changed the sticker on the housing, I have no idea. They only commented that things are different with Chinese products, and yet they look at these data with a grain of salt. However, they prefer proven brands where they can be sure that the given parameters are 100% consistent with reality.

6 minutes ago, aemx88 said:

Thank you for the update. Much apreciated.  In my R8 the original choke was replaced with Hammond 194 and it was the Hammond that got melt?!? Talking about luck .   I’m looking to replace with a larger toroidal choke transformer . 
 

glad to hear your R8 is up and running 

 

I was told that if I replace only the choke, it will not help, because when there is an unusual increase in the voltage in the network, e.g. from standard 230-235V to 245V, the choke and several capacitors will be damaged again. To avoid this, you need to replace capacitors with a larger capacity + additional fuses. Replacing just the choke is not enough.

Questions about bias:

If the bias-needle is a bit to the right, is that 'over-biased' or 'under-biased' ?

Is it possible to hear any difference if the bias-needle is a bit to the right (all 4) or a bit to the left?

 

Edited December 4, 20241 yr by Tube

9 hours ago, Tube said:

Questions about bias:

If the bias-needle is a bit to the right, is that 'over-biased' or 'under-biased' ?

Is it possible to hear any difference if the bias-needle is a bit to the right (all 4) or a bit to the left?

 

 

If it's set to the right it's going to appear to be overbiased but not necessarily overbiased for the given set of conditions. You would need to measure the actual plate voltage and current to ascertain those parameters. Tonal characteristics for slight adjustments in bias (say up to 5% of plate current) would not be audible.

Well my R8 has been sold! Someone bought my ISO transformer upgraded amp and they are super happy with the way it sounds. That pretty much ends my journey with that amp and it's been a fun ride. Time to move onto other projects 🙂 My email is stephe@skunkiedesigns.com if you have any questions. Cya!

On 02/12/2024 at 10:40 PM, mindhead1 said:

I just added the Horizon 6SL7 to my R8 and I have to say I’m impressed. I’ve had my R8 for about 3 years and rolled more tunes than I care to admit. 
 

Current tube complement are the Psvane 4 x KT88-T MKII, 2 x CV181-T MKII, 1 x NOS Sylvania 6SN7 and the Horizon 6SL7s. 
 

Prior to the Horizon 6SL7 I had Tung-Sols, rebased NOS Sylvania 6SL7s. These tubes were OK, very dynamic compared to the stock tubes, but ultimately a little to hot in the treble for my liking so I always defaulted back to the stock 6SL7. After reading the positive reviews of the Horizon tubes I decided to give them a go before selling the R8 and moving on. 
 

The Horizon tubes are delivering a smooth and non-fatiguing top end with good dynamics and holographic soundstage. I think I’m good for a while and will not be selling the R8 anytime soon. 

 

3 weeks in...
The Horizons are revealing so many details in the music. Details in the music I never heard before. And they sound good! 

 

Hi all,

 

One on my bias pot is jammed up, it gets very stiff to rotate compare to the others. It's time for me to bring out my soldering iron and while I'm at it, just wondering if anyone has successfully replace the PT with an alternative? Thanks!

My bias pot had the same issue.  It was okay but later went bad as described. Right after the pot went bad the power tube it controlled red plated. I would replace all four pots immediately as they are a known weak point in the amplifier.  My Muzishare X7 had the same issue. I used the Bourns pots as replacements as they are a direct match with the originals other than being a little bit smaller than the originals (they are made of plastic so you have to be careful installing them as they melt easily, so buy a spare).  IIRC they were ~ USD 6.00 each. They are rated for 50,000 cycles of use so they should be pretty reliable. 

13 hours ago, jon96789 said:

My bias pot had the same issue.  It was okay but later went bad as described. Right after the pot went bad the power tube it controlled red plated. I would replace all four pots immediately as they are a known weak point in the amplifier.  My Muzishare X7 had the same issue. I used the Bourns pots as replacements as they are a direct match with the originals other than being a little bit smaller than the originals (they are made of plastic so you have to be careful installing them as they melt easily, so buy a spare).  IIRC they were ~ USD 6.00 each. They are rated for 50,000 cycles of use so they should be pretty reliable. 

Thanks Jon, parts are on the way, should be able to work on it this weekend along with a few other replacements.

Hello,

 

Just had a tube red plate.  I turned off the amp right quick.  I replaced the tube with a stock one, turned it back on and she sounds fine.  Let me ask a question: do I need to replace the stock tube with a matched one to the others, or can I leave the stock tube in and get away with it?  

 

Thanks. 

I must be lucky... Really lucky... The person who gave me the Mullard XF2 EL34s just dropped off another set of really rare and expensive tubes and my jaw  just dropped to the floor. I got a trio of Sylvania JAN-6SN7W Metal base tubes. a trio of the rare Tung-Sol "Black Bottle" VT-229/5SL7 tubes and a pair of Sylvania 5691/6SN7 red-base tubes (made by RCA). Popping in the Sylvanias and the Tung-Sols made for an amazing sonic experience. He said that the Sylvania 5691s are not as smooth as the Tung-Sols.

 

The gifter has tons of tubes. I spent all day testing tubes for him.  Mullard XF1/XF2/XF3/XF4 EL34s, Sylvania 6SN7-WGT, Sylvania VT-231 "Bad Boys", Siemens EL34s, Amperex EL34s, GE and Sylvania 6CA7s, RCA 5691/5692s and the list goes on... Sadly a number of the Mullard EL34s were bad, some measured dead and others had white getters.

 

He said he has another couple hundred tubes, some which I can't test with my MaxiMatcher testers. He is very busy and can only come about once a month to test tubes, bringing about 50 at a time.

 

36 minutes ago, Haecate said:

Hello,

 

Just had a tube red plate.  I turned off the amp right quick.  I replaced the tube with a stock one, turned it back on and she sounds fine.  Let me ask a question: do I need to replace the stock tube with a matched one to the others, or can I leave the stock tube in and get away with it?  

 

Thanks. 

If the red-plated tube still works, you should be okay but you have to be careful. If it red-plates again it could damage the transformers as well as other components.

 

How does the tubes bias?  Is it normally or does the bias fluctuates?  Is the bias pot "sticky" or hard to turn?  The OEM pots are  known to fail. I had one pot fail in both my R8 and as well as my Muzishare X7 amps. Before they failed, the pots started getting hard to turn. Unfortunately, the pot did fail in my Muzishare X7 and it took with it the Gold Lion KT-88 tube with it. I ordered a bunch or Bourns potentiometers as they are a direct match with the OEM pot in specs (unlike the Vishay which requires some modifications to the circuitry to get it to match the amps ).  Both Bourns and Vishay are rated for 50,000 cycles of use so they should be reliable. As mentioned before, the Bourns are made of plastic and can easily melt if you apply too much heat  when soldering. Also, the Bourns are physically smaller so the pot shaft is shorter and a bit smaller in diameter. The Bourns pots are cheap, several dollars for one. So I would recommend you replace all four at once to be on the safe side.

 

They can be found here...

Edited December 19, 20241 yr by jon96789

Thanks Jon.

 

The tube biases fine. It doesn't fluctuate at all. The pot is not hard to turn.

 

I turned the amp on, it did its self-check, and then I noticed the tube in V1 started to glow bright red, and sort of hissed, then I smelled something, but the socket looks fine and so does the tube. 

 

What is weird is the tube looks fine, and so does the socket. Of course, I know next to nothing about all of this, so there's that too. 

5 hours ago, jon96789 said:

I must be lucky... Really lucky... The person who gave me the Mullard XF2 EL34s just dropped off another set of really rare and expensive tubes and my jaw  just dropped to the floor. I got a trio of Sylvania JAN-6SN7W Metal base tubes. a trio of the rare Tung-Sol "Black Bottle" VT-229/5SL7 tubes and a pair of Sylvania 5691/6SN7 red-base tubes (made by RCA). Popping in the Sylvanias and the Tung-Sols made for an amazing sonic experience. He said that the Sylvania 5691s are not as smooth as the Tung-Sols.

 

The gifter has tons of tubes. I spent all day testing tubes for him.  Mullard XF1/XF2/XF3/XF4 EL34s, Sylvania 6SN7-WGT, Sylvania VT-231 "Bad Boys", Siemens EL34s, Amperex EL34s, GE and Sylvania 6CA7s, RCA 5691/5692s and the list goes on... Sadly a number of the Mullard EL34s were bad, some measured dead and others had white getters.

 

He said he has another couple hundred tubes, some which I can't test with my MaxiMatcher testers. He is very busy and can only come about once a month to test tubes, bringing about 50 at a time.

 

You sure are lucky!

Those Tung Sol vt229’s are very nice. I have a pair, they sound very airy without being harsh. 

14 hours ago, jon96789 said:

If the red-plated tube still works, you should be okay but you have to be careful. If it red-plates again it could damage the transformers as well as other components.

 

Jon do you mean I can use the tube that red-plated again? It was smoking before I took it out.

I wouldn't trust the tube that red plated.

 

I'd also check the resistors around that socket that smoked. If something was emitting smoke It was likely a resistor.

Edited December 19, 20241 yr by muon*

Well, it was odd. I turned the amp on, and within a moment I heard static, and saw the tube glowing very red. I turned it off as soon as I saw it. I did smell *something* but can't remember seeing anything smoking. I put one of the old stock tubes in its place, fired her up, and after biasing, I checked to see if the sound was fine. It was. I am going to get a matched replacement for the Svetlana that red-plated. I have been told that I can't use one stock Willsenton tube with the other three good Svets. 

1 hour ago, Haecate said:

 

Jon do you mean I can use the tube that red-plated again? It was smoking before I took it out.

If it smoked, then the tube is no good... If you caught the tube immediately when it red plates, it is possible that the tube might not have gone into a self-destruct mode. Chances of saving a red-plate tube is slim but possible but some damage will likely have been done. If a tube does red-plate, the reliability and the lifetime of the tube is greatly reduced.

Yeah, it looked like it smoked, but I can't be sure. I base that off the smell afterward. Is there a way I can test it? Can I put it back in the amp, turn it on, and see if it is fine, or am I risking damage to the amp doing that? 

29 minutes ago, Haecate said:

Well, it was odd. I turned the amp on, and within a moment I heard static, and saw the tube glowing very red. I turned it off as soon as I saw it. I did smell *something* but can't remember seeing anything smoking. I put one of the old stock tubes in its place, fired her up, and after biasing, I checked to see if the sound was fine. It was. I am going to get a matched replacement for the Svetlana that red-plated. I have been told that I can't use one stock Willsenton tube with the other three good Svets. 

Be careful... A tube does not normally red-plate on its own unless it is well used... In the case of a power tube, you normally can expect about a thousand hours from a Chinese tube, maybe 1,000-2,000 hours on a Russian tube if both are new. Vintage NOS tubes can last 2,000-4,000 hours (they don't make 'em like they used to). 

 

Figure tubes are like light bulbs, they can fail at any time. Some can last a long time, some don't.  You cannot determine how long a tube will last if it is used.  A component failure is possibly the cause. Did you notice any sort of burning smell from the amplifier?  You need to keep a good eye on the amp to make sure nothing happens in use. 

Well, I got those Svets in March of 2022 so *maybe* I have put 2000-4000 hours on them.

2 minutes ago, Haecate said:

Yeah, it looked like it smoked, but I can't be sure. I base that off the smell afterward. Is there a way I can test it? Can I put it back in the amp, turn it on, and see if it is fine, or am I risking damage to the amp doing that? 

if the amp has a smoking smell, then it has likely a failed component, most likely a burned resistor or a failed capacitor.  It is also possible that the bias pot failed (but you said it still functions so this is unlikely). In either case, I would strongly suggest that when you have the amplifier serviced that you replace all four bias pots as they are a known but occasional issue. The thing is that there are four bias pots, which means the chances of one failing is four times higher.

 

You should have it checked out.  Luckily, the R8 is a simple component to component design, i.e. point to point wiring. It is easy for any competent service person to examine and repair. It does not have any big circuit boards with integrated circuits that would need to be examined.

I finally was able to sit down and listen to the Mullard XF2 EL34 tubes. TBH, I  could not hear a significant improvement in sound over my Groove Tubes EL34M.  The comparison was pretty close with the Mullards having a smidgen better soundstage and imaging. I wound up playing back the SACD soundtrack of the original 1987 "Blade Runner" music by Vangelis. This is where the Mullards really shined. The soundtrack is a compilation of electronic music that has some very complex sound effects and movement. The Mullards exhibited more air and precise movement of the electronic wizardry that Vangelis supplied. The differences were not insignificant. To  me, the Mullards can really struts its stuff with music that has been mixed with careful movement in the image.

 

The accompanying tubes in play were my NOS Tung-Sol 6SL7 "black bottle" tubes with the metal-based Sylvania 6SN7W tubes (sorry to say, but the Tung-Sols outperformed the RCA 5691/6SL7 "red-base" tubes which sounded quite similar to the Sylvania 6SN7GT/VT231s).

 

I cannot imagine a better tube combination on the R8. The Groove Tubes EL34M are very good, there is nothing to be embarrassed in its sound. On most music, it is nearly equal if not equal to the Mullards, but on some music there is no comparison. All the current production EL34s cannot touch the Mullards, it is not even close. The current Psvane and Shuguang Chinese EL34/6CA7s sounds shrill and flat in comparison. Ironically, I can only recommend the current production Russian-made Mullard EL34s as a suitable alternative in the current crop of tubes. It comes only about 75-80% to the real Mullards. The Groove Tubes EL34-Ms reaches 85-90% of the Mullards sonics, but the rest of the field falls in the 70% range.

 

If you can get your hands on a set of Mullard EL34 XF2 tubes, grab 'em. Sadly, these tubes are getting harder to find as time goes on. They are no longer made and the limited inventory gets smaller and smaller as times goes on as people snatch them up, which means these tubes will be either unobtanium or even more exorbitantly expensive.

Got my parts from Mouser, will be busy this weekend with replacing the bias pots, adding a few more resistors and caps., to reduce the risk of run away Current.

I found a seller in Japan for 2 x Iso Tango for $900 AUD and will pick them up next Feb when I'm in Tokyo. I still want to replace the Power trany but not sure which one to get, that mismatched colour of OPT will probably drive me insane 😓