[Rico613]

  For my taste and the kind of music that i listen, i usually use 2 differents tubes with my TH900 : tung sol round plate 6F8G or Fivre 6SN7 gt.
Bur i also not use 300B output tubes like you, but PX4tubes : more neutral and dynamics than 300B.

300B tubes are thought of as sounding highly musical, warmer, and with a lush full sound.  I've been listening carefully to my EML 300B Mesh Plate, and for chamber ensembles of 3-5 players it is fabulous. This tube adds it's own drama and musicality that works well for solo performance and small groups.  
 
A couple years ago I talked with the distributor for KR tubes in the States.  He said that sometime after the founder of KR, Riccardo Kkon, died in late 2003 his wife was unable to mange the business and the quality control suffered and they eventually stopped production.  I don't know the full story but that's what they guy said.  Here is an interview with Dr. Kron from early 2003:  http://www.6moons.com/industryfeatures/kraudio/kraudio.html
 
EML is planning to make PX-4's one of these days and I'm sure they will be great.

 

[r one]

They are very friendly. I've already talked to them about the KR 300b and they always respond quickly. Let me know if the PX4 are still available from KR or not, this is something that interests me too.

 

[r one]

  Just got their reply:
 
"Yes, I can sell and ship to USA, there is no major problem about that. The purchase process is very simple, you tell me what you are interested about, then I prepare the Invoice and the payment can be done using PayPal or even a direct bank transfer.
But first of all let me know which tubes you would be interested about, in order to check if I have them available. If not, anyway, it will only ask a few days more, time for me to get them from KR.
Kind regards, "
So, just email (info@ceresaudio.com) them which tubes you need and they can go PayPal

They are very friendly. I've already talked to them about the KR 300b and they always respond quickly. Let me know if the PX4 are still available from KR or not, this is something that interests me too.

 

[r one]

  He said that sometime after the founder of KR, Riccardo Kkon, died in late 2003 his wife was unable to mange the business and the quality control suffered and they eventually stopped production. 

You mean PX4 production or all KR tubes production ? Actually, the factory is still alive apparently and all of their tubes are on their website
 
I've heard recently a 300B tube on my BA (standard EH300B) and I liked that sound. But it was a little too warm and soft compared to my usual listenings.
The problem is that I've built my audio system from the PX4 tube. My master7 dac in particular was chosen to add some richness and analog sound to the PX4 which they can be too dry with a delta sigma dac (my violectric V800 for example.). My PX4 must have about 3000 h. I hope they will continue to work well for some time. If I don't found it for replacement when they'll be dead, it would not be a drama but it would be embarrassing.
In this case, i think i will pick up a 300b eml solid plate tubes.

 

[SoundApprentice]

I've always had good experiences buying tubes from Langrex. www.langrex.co.uk
 
The website has a good variety of tubes to buy direct, but they also have a huge stocklist that you have to call or email to order off of. I just picked up 5 pairs of NOS 307A tubes for my BA which are getting harder to find stateside.

 

[ericfarrell85]

You mean PX4 production or all KR tubes production ? Actually, the factory is still alive apparently and all of their tubes are on their website

I've heard recently a 300B tube on my BA (standard EH300B) and I liked that sound. But it was a little too warm and soft compared to my usual listenings.
The problem is that I've built my audio system from the PX4 tube. My master7 dac in particular was chosen to add some richness and analog sound to the PX4 which they can be too dry with a delta sigma dac (my violectric V800 for example.). My PX4 must have about 3000 h. I hope they will continue to work well for some time. If I don't found it for replacement when they'll be dead, it would not be a drama but it would be embarrassing.
In this case, i think i will pick up a 300b eml solid plate tubes.

Yeah, I can tell you that the EML Solid Plates can sound fantastic, but also, a little sterile and boring with the wrong driver tube. For instance, the HD800 is a headphone with noted synergy via the ECBA. Yet, for two years I never could get into the sound with this amp. The Zana Deux was simply a better fit, although strident in the upper range. So, one day, I decided to replace the Sophia Electric 6sl7 with a RCA Grey Glass VT-231 and that lauded synergy appeared as though by voodoo. A mesmerizing combination, with a tamed top, and beautiful euphonic mids. The HP1000, similarly, was bland with both the Sophia and the famed Mullard ECC35, and damn near perfect with a NU Black Top 6sn7gt. I'm honestly of an opinion that "neutral" or more "analytical" oriented cans work best with the 300B. For the life of me I am not impressed with the TH900 out of this setup. Judging by what I learned above, the driver tube is especially important when running the Solid Plates.

 

[r one]

Yesterday, i've sent a mail to Kr audio in Czech Republic and asked about her currently production tube.
Eunice kron answered me this morning very kindly.
The company always product all the tubes you can see on the website. She told me that PX4 are very used in european and japanese audio amplifiers. PX4 and PX25 were invented by Osram with original english base UF-4. But if you want a pair of KR PX4 in UX4 base (invented by western electric for 300B tube), no problem, just request. They made it on demand.
 
I'm happy and reassured for the future. Someone know how many hours this kind of tube should be work ?

 

[r one]

Hello guys

Recently I have to change my 6x4 rectifiers tubes. What are all equivalents code that I could use in the power supply unit ? 6x4 , EZ 90 and..?

 

[Rico613]

Hello guys

Recently I have to change my 6x4 rectifiers tubes. What are all equivalents code that I could use in the power supply unit ? 6x4 , EZ 90 and..?

Those are correct, there is also a QM 556 listed as a rugged 6X4  here:  http://www.g8wrb.org/data/military/MIL-HDBK-213A.pdf
 
I have two pair of vintage Mullard EZ90, PM me if interested.

 

[zeissiez]

Do 300B tubes sound fuller/weightier than PX4? How about soundstage size?

 

[r one]

 
Those are correct, there is also a QM 556 listed as a rugged 6X4  here:  http://www.g8wrb.org/data/military/MIL-HDBK-213A.pdf
 
I have two pair of vintage Mullard EZ90, PM me if interested.

thanks for this.

 

[r one]

Do 300B tubes sound fuller/weightier than PX4? How about soundstage size?

I listen everyday with some KR PX4 and have listen with EH 300B too during one month.
PX4 is more dynamic with better impact and clarity, bass is more speed and tight but less sirupy than 300B. Soundstage is equal. I like two versions, but sometimes 300B is too promeminent in mid bass (with modern electro music for example). I think that PX4 tubes are more polyvalent with all kind of music.

 

[Rico613]

I had excellent results with EML 300B XLS.  I'd highly recommend these.

 

[zeissiez]

I have my BA with a pair of PX-4. If I want the BA to sound lush and full, which 300B should I get?

 

[Rico613]

I have my BA with a pair of PX-4. If I want the BA to sound lush and full, which 300B should I get?

I had both EML 300B Mesh Plate and EML 300B XLS.  The Mesh Plate is very lush - probably too much and thus lacking some detail.  The XLS tube sounded fabulous with a warm, lush sound and with outstanding precision and detail.