I have the CJ5 monos. 8 per mono. The beauty of "our" amps is the amp trim pots do the work.--No matching necessary. I use the Seimens,what brand are in there now?-What brand are you looking at?
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The amp currently has Electroharmonic from the manufacturer (Manley neoclassic 250).
I have had recommendations of JJ or Svetlana as being superior to the EH, but don't have experience with either of them (I guess you can tell I am new to tubes). NOS prices seems to be out of the question, but I would investigate any reasonable recommendation. I am assuming that the Seimens are NOS and sound similar to the classic Mullard sound that is in such high demand. I have heard that some of the new production tubes sound close to the classic Mullard sound.
I don't know if tube recommendations are especially system dependant, but that is probably another thread.
No, tubes are listener dependent. For my CJs everybody and his brother recommends Svetlana; I have a complete set:( I've stuck them in twice) Not the same as Siemen; they have this magcal top end the Svets. lack.
As Albert pointed out in another post; your tubes are Russian Sovietec--(sorry 'bout the spelling--);and are similar to Svetlana.
I paid 50bucks ea for my Siemans.--Haven't heard the Mullards so I can't comment on 'em.
As Avguygeorge says, different tubes sound different in various amps. I have no direct experience with your Manleys, but would rate EL 34's in general in this order, good performance to best: (I own all of these.)
Sovtek / Electro Harmonex EL 34
Svetlana EL 34
Tesla E 34L
Siemans / (late 70's) Telefunken EL 34
Amperex EL 34
Mullard EL 34
MO Valve KT 77
The prices are about the same from the Sovtek through the Siemans, give or take a little. The curve gets mighty steep about the Telefunken and Amperex part of the curve, with the MO Valve KT77's bringing (probably) $300.00 each in original boxes.
Used Mullards at about $60.00 to $95.00 each on EBAY are pretty much the best performance available for the high end price. The Tesla is my choice for low price, being about the same as EH and Sovtek.
Each of these has a different personality. Depending on the associated equipment and cables, you might even disagree with everyone else as to what sounds best.
Don't forget the other tubes in the circuit. They are often a fraction the investment of replacing all the outputs, with equal (or sometime) greater differences in performance gain.
Almost forgot, I would not buy specially graded or matched tubes, especially new ones. New tubes will be sufficiently close to work fine in your amp.
For used ones, the trans conductance ratings on the advertisers notes should promise at least 80% of their original numbers. In this case as well, that is sufficient.
The Sylvania tube is good from a reliability standpoint, and they are fairly free from microphonics. The reason they are cheap is because they typically do not sound good. This assuming that the Cca designation does not mean they are actually Siemens built for or relabeled by Sylvania.
The best sounding 6922 (6DJ8) is the Telefunken, second is a toss up between Mullard Gold Pin 6922 and the Siemens Cca. Other good choices in this category is the USA Amperex 7308 CEP. This is a military tube with very neutral tonal character and very low distortion.
The tube type sound that I find attractive is not really present in the Amperex. The warmest is the Mullard and Tele, which is probably why they are so sought after and expensive.