Retubing CJ 140 amp

Has anyone retubed a CJ 140? It appears all tubes are Sovtek. Has anyone tried Svetlala 6550? Any better or worse?
Also small tubes replacements ,any suggestions.
Many Thanks
The output tubes in the 140 are Svetlana 6550's, not Sovteks. I have aksed Lew Johnson this.
I have just changed my tubes to EH KT88. Differences in my system is a slightly tighter bass and perhaps a little more treble extension, which is what I was looking for. mid's are similar.

cheers Shane
hi guys, i'm glad that someone has started this thread as i'm in the process of buying a 140 and was keen to find out what more performance can be squeezed out of it. Whilst I realise CJ have voiced it using current production tubes, decent nos tubes can probably improve matters further. I did approach CJ on the subject, however they gently tried to dissuade me from replacing any of the tubes. In the case of the KT88/90s, they pointed out that achieving the correct bias may be difficult given the led system used. I suspect my initial route will be to try a nice nos 6922 as a starting point, maybe an amperex pq or mullard. The 6h30s are more challanging however I've got some cryo'd versions on order from HAL-O tube dampers are also likely to make an appearance, and I may start saving up for some more blackplate tung-sol 6550s......Has anyone else got any other experiences / ideas to contribute? Also what power cords work well?
I have used the 140 with stock tubes and have had no complaints. The real trick to making this amp sing is a very good front end. I have retubed other amps using NOS and it can get costly and frustrating. I think the idea of attacking the 6922s is a realitic start. Amprex will more than likely be the way to go. Siemen CCAs will be fast, clean (quiet), accurate and musical, but a little thin in the upper midrange. They also get you close to the performers being in your room. The Telefunkens place them in the room behind the speakers (not to be confused with a deep soundstage, but rather recessed). Telefenkens will also be drier, albeit fast and quiet with a small soundstage. The Amprex will give you all that the CCA does, but add some body and warmth to the midrange without making it bloated. But these are what my ears have told me.

Regardless, try the amp as is first. If you are going to tube roll look at the cost and see if you can use that money eleswhere in your system first. The 140 is a keeper out of the box.
I should clarify. I do not have the prem140. I have the prem8a monoblocks.
Just wanted to clear that up before i send someone down the garden path.
Lew at cj did not recommend going to the KT88's, but I think that is more from a realibility standpoint. he indicated that in prem 8a at least the adjusting the bias for 6550 and Kt88 was the same.
Not sure if I can afford going to monoblock 140's anymore. I am going to have a listen to the ACT2 pre amp in a few weeks. The prem 16 is starting to show its age, with a Hovland HP200 sound more transparent and a tighter bass.


I've just received a cryo'd nos 6h23 (6922 replacement) from; this is already sounding very promising despite despite not having burnt in.