[dminches]

Not yet.

 

[levlhed]

12AT7 and 12AU7 seem to work just fine.  Less gain as expected.  I haven't determined anything different that couldn't be attributed to the lower gain or  specific tube characteristics yet.
I tried 12AT7 Telefunken's (ECC801S) and there wasn't really that much less gain.  It seemed like I could get one more click higher? Like 20 click versus 19 before the drivers start to grumble.
Currently plopped 12AU7 Tele smooth plates in, certainly a difference in gain. In the ballpark of 30 clicks before driver starts to complain.  The 3dB bass boost doesn't seem to cross the "too much" line with these 12AU7's.
It seems like things start getting congested at the upper volume.  Note that this is louder than I'd ever listen anyway.  At normal volume levels it seems about the same as far as life, juice, special sauce - just able to turn the volume dial up higher.  I haven't really spent enough time with the amp to qualify more minute differences.  Hard for me to say whats "better" at this point.  My gut instinct is that it is better with the 12AX7's, but my initial impressions are that the Leben CS-300XS works just fine with the lower gain tubes and I suspect that people could find some more magic tube combos with some experimentation.
What's nice for me now is that I have many more options on hand and don't need to dish out more cash right now just to play around.  (my wallet is rather thin for the foreseeable future!!)
 
It'd be cool if some of the other owners gave it a shot and let me know their results.

 

[HPManiac]

Hi All,
 
I've just joined the CS300X club and this thread is tempting me to start rollin' them tubes. I can get hold of Mazda, Tungsram, CIFTE, RadioTechnique 12AU7s, and Tungsol 5751s. Any recommendations out of this selection and any opinion on RFT EL84s?
 
Thanks.

 

[Skylab]

I know from experience the Tung-Sol 5751's are nice.  I don't have any experience with the others.

 

[bigdish]

Hi everyone, I got a Leben CS300 and am wondering who has tried to modified it and what are the results. 

 

[Skylab]

It's not an amp I would modify.  If you want a tube amp to modify, buy a vintage Scott, Fisher, or Dyna.

 

[Clayton SF]

Here's a Leben CS300X that was modified with V-Caps, etc.
 
Leben CS300X [Custom Version]
 

 

[dminches]

Is that yours? Any thoughts on the effect on its sound?

 

[Clayton SF]

Quote:

Is that yours? Any thoughts on the effect on its sound?

 
It is not mine. I just remember reading an article about someone's custom Leben and thought that I'd pass it along.

 

[dminches]

Is there an undeserved obsession with v-caps? Do they make a significant difference ?

 

[Clayton SF]

Quote:

Is there an undeserved obsession with v-caps? Do they make a significant difference ?

I believe that V-caps do make a big difference. But to appreciate its impact it is of personal taste. I have a Woo Audio 4 with V-caps and the sound is heavy compared to a WA4 without V-caps. The V-caps place the sound signature in the thick-sounding arena which can be tamed with bright headphones like the Beyer DT990 600 ohm.

 

[dminches]

I know you have a very nice collection of amps so I appreciate your comments.

 

[bigdish]

I read the same article also. That's why I am curious to what extend can these modifications improve the sound quality.
  
 
Here is the article:    
  
http://www.highfidelity.pl/@main-135&lang=en    

 

[Anders]

I have modified my Leben CS300. It happened after the amp was damaged in a tube-rolling accident and an resistor blew up. This can seem dramatic but in this case the damage was benign and easy to repair. I brought the amp to a very experienced tube technician and also accepted his recommendation to change the coupling capacitors, with a restore guarantee without cost.
 
At the same time, I showed him some upgrades from the Polish magazine and the upgrade capacitors in the CS300XS (compared to CS300). There are a few capacitors that are different and he said that the capacitors in the XS are better but that the importance for sound quality was marginal or maybe not audible. This is very much in accordance with Skylab's impressions from listening. He said that the component in the amp are not expensive but of good quality and build quality is very good.
 
I think that the improvement of the upgraded coupling capacitors is substantial. The upgrade capacitors are Duelund capacitors made in Denmark. Duelund capacitors have a good reputation as high-end components. They are unfortunately expensive and four are needed. You can see them on the picture. I have placed one of the original capacitors above the third Duelund resistor from the left in the picture for comparison. They are much bigger but are not of different capacitance value.
 
It is difficult to evaluate the change in sound in such modifications. The upgrade took some time and the new capacitors have to burn-in. I have not had any possibility of an A-B comparison to an unmodified Leben but I am convinced that sound became smoother with better dynamics and improved bass impact. The difference is substantial.
 
 

 

[bigdish]

Sound promising! I'd also like to give it a try. Has anyone tried to replace the output transformer?