Conrad Johnson LP 70/140/275 Tube rolling

A cautionary note here. Do not according to cj, replace the 6922s in the LP140M with NOS, etc tubes. It can make the amp unstable. CJ specifically matches the 6922 for the exact position in the circuit.

The other two amps, for whatever the reason, are not as sensitive. I've had my 140M and haven't played with the small signal tubes and they've run perfectly since I got them. I'm not going to play with danger :)

BTW, the biggest improvements I've heard with the amps come with cables.

Myles

Hi Ole,

Glad to hear you're enjoying your cjs! The cjs work great on my ML Summits--but cjs love Maggies too because of their constant 4 ohm load. (I assume that you have had the factory set the output impedance to match your speakers eg. 4 or 8 ohms? The amps as I remember come set at the factor at 4 ohms--and with a speaker that's between the two, cj recommends the lower of the two impedance settings.

Wish could give you an answer as to why the 140 is more sensitive than it's siblings to the choice of input tubes but don't know the answer :)

As far as the sounds goes, the amp definitely is a distinct step up from the Prem 12s! It is fairly revealing and you will hear the good and the bad from your albums. But otoh, perhaps there is something else in front of the amps that is adding some brightness to the system like the front-end/cartridge or phono section? Maybe a little VTA adjustment might go a long way to making your albums sound better-esp. with the vast majority of today's MCs that are pretty VTA sensitive.

Myles

Hi AB-

There's a difference in the cautionary warning note between the amp and preamp. CJ states in their manuals that they have selected the best tube possible eg. of what's available and then they burn them and select the best of the best using their in circuit performance (that arguably is the best way to do it). One of the things that cj obviously selects for is tube quietness-as one can hear with their selected phono tubes.

Now with the amp, I was talking about the possibility of damage, not as in the case of the preamp with degradation of the piece's sound. Now are the cj tubes the best sounding tubes? That can be argued but they are probably the most reliable tubes that one can use. And all one needs to do is go back a couple of years and hear how many audiophiles were turned off to buying tube equipment because of relability issues.

That said I have tried different tubes in my cj TEA 1bc phono section. I've compared probably a half dozen or more brands in the unit (Mullard 10m, Tele rib plate, Amperex, Mullard early '50s, Siemens dual post, etc) and ended up using the Tele rib plates. Now the tele rib plates are not as quiet as the stock tubes--and that may be an issue for those using LO MCs--but they sound much better.

Now one might be inclined to go to the several tube sources that sell selected tubes -- but how long will these tubes stay quiet and there's the question of cost. Yes one can use some Tele CCAs in the ART preamp--but at the cost of what $300 or more times 10 tubes, we're talking about a small fortune, even if one says these tubes will last 10,000 hrs (and they may last, but how long will the sound good for?).

Now could different 6922s sound better than the stock tubes in my GAT? I don't know but someday will try some of the tubes have accumulated.

Cheers!

Myles