Tube Rolling | Luxman CL-38uc

I got good sound with RCA cleartops, and better sound, for a higher price with NOS Telefunken tubes in mt CL-38uC

Thanks for the quick reply @jperry :)

Was wondering, did you change all tubes?

What do you think about just changing the 3x 12AU/ECC82 on the center section? (see my initial post)

Let me know,

Thanks!

I changed all of the tubes.

If you are only using certain tubes and they are the only ones you hear, then it should work.

I don't know enough technical stuff to comment on your diagram, etc.

You can change out the 12AU7s with another brand, and you might even be able to substitute a 12BH7a, but the 12AX7 has a lot more gain than a 12AU7 so I don't think those are interchangeable in that application. 

Hey, did you try rolling those tubes? I have the same amp and have been tempted to try something similar. I actually had the same questions as you regarding just changing the ones you highlighted. let me know!

Hi!

Yes, those are the right tubes :) ... only 3 would be needed if you are not using phono input or tone controls.

The only caveat is that they are placed a bit differently inside on the actual unit, so a "best guess" would be needed unfortunately on picking which ones to replace. The phono input ones are clearly distinguishable, but the others not so much :(

Haven't taken the time to do that quite yet, but will try to report back when I do.

Hope that helps!

my 2 cents

i don’t have this particular luxman pre... so this is from general knowledge and a lifetime of tube rolling

12au7 and 12ax7 are usually NOT interchangeable... vastly different gain characteristics (that is why those three tube types were designed and made in the past, despite the common 12v heater dual triode small envelope designs -- 12au7 vs 12at7 vs 12ax7 - very different gain profiles from one to the other -- 1x 3x 5x gain, thus applicable for different circuits)...you can bet that putting in a 12ax7 with 5x the gain of a 12au7 in your nice luxman will create problems

you would need to contact luxman, or a knowledgeable dealer or tech to confirm specifically which three 12au7 slots are for main amplification, not tone control buffering circuitry (what is drawn on the circuit diagram is idealized, the actual circuit board may not be laid out in exactly the same fashion)... you CAN safely swap in different 12au7 tubes in those 5 positions, but without knowing for sure, you won’t be able to assess what you are hearing in the attempt to tube roll

here is a fairly complete discussion and listing of 12au7 equivalents (these are different names for the same tube, from different parts of the world, or very very similar variants made over time i.e. improved ruggedness etc etc - with identical or very similar gain profiles) - you would be well served to read it carefully and completely

http://www.audiotubes.com/12au7.htm

Hi @jfandr147 and all - I have the CL-38u and CL-38u-SE models, the tubes of which are laid out the same as in the 38uc. 

I don't know how to post an image, but I've spent some time under the hood of the 38u, traced out tube signal flows, and can describe for you the location of the tubes in question.

With the faceplate facing you, there are two rows of four tubes; a front row and a back row. For purposes of this description we'll call the back row tubes 1 through 4, from left to right. The front row holds tubes 5 through 8, from left to right. For reference, the phono tubes (with cages) are positions 3, 4, and 8. Tube positions 1 and 5 are for the EQ section. The tubes not involved in phono or EQ sections are in positions 2, 6, and 7.

I haven't done much in the way of tube rolling but can assure you with confidence the above is accurate.

I hope this helps - I'd love to hear back on any experiences with the tube rolling.

well done @acefactory -- here is a pic to accompany your excellent description

so the tubes op wants to roll are three of the four middle ones (leaving aside the one single middle one with the white spring loaded tube damper/cage)

Thank you so much @acefactory ! you just saved me ton of time trying to figure that out! :) ... I'll report back on how the tube rolling goes, will try a set of Telefunken and Mazda tubes.

@jjss49 thanks for the picture, comments and your initial remarks regarding tube differences. You are absolutely right, better to stick with 12AU tubes in this case as intended (that's what I ended up doing).

Wonderful!! This is really helpful. Looking forward to hearing back on some rolling results. 

wow this is a lot of help.   I wasn't sure about tube position either.

If anyone has done some rolling please post it up

So does the EQ have 2 tubes, the phono stage has 3, and the line stage has 3, ecc82 tubes? 

I removed that horrid sounding 12au7 JJ tubes, and put Genalex Gold Lions instead. Much better sound. Very smooth. The only drawback is the cost.

Mullard 12au7 are great sounding smooth tubes $25 USD ea.

Telfunken ECC82 12au7 $80 each 

For me my favorite 12AX7 has been the Telefunken Smooth Plate NOS or even the ribbed plate. For the 12AU7 I've been happy with the Telefunken ribbed plate or a Mullard NOS. 

@brubin where do you get Mullards for $25 and TFs for $80?