Design Trend in Some Newer CJ Preamps

[Truth71]

Some of the newer CJ tube preamps (ET7, ET6) utlize only one vacuum tube.
- Do these designs eliminate tubes by employing solid state devices?
- Are they "harder" on tubes ?

[AnotherJohnson]

They’re using the tube as the amp. It’s typically a 6922.
I’ve gotten about a year out of it in my ET3SE and ET7S1.

So far no replacement needed with my ET7S2, but I haven’t had in service for a full year yet. Maybe 10 or 11 months.

I was a bit miffed when my ET3SE needed a tube in what I considered a short amount of time. But the tubes are of modest cost, and it has been easy to know it was time to replace by the slight elevation in the noise floor.

As you know, the 6922 is a twin triode, so one tube can serve both channels.

No guess work to figure out what tube is out of spec since there’s only one.

The circuits are as simple as they can make them. I’ve been very pleased with the transparency, but YMMV. There is a high current mosfet buffer on each input which reduces the sensitivity of the preamp to interconnect choices.

[Big Dog RJ]

Yes, correct as AJ pointed out.

With these new designs, CJ's circuits are getting ever simpler... far less parts used with very high quality. I guess the tubes do run harder as compared to an array of tubes but then that array of tubes can cause more noise, microphonics and so on. So having just one or a pair is probably the best way to go.

I did also did notice that when I compared the ACT2 with the CT5, although the ACT2 offers more bass and LF detail, the CT5 is smoother. It also runs less hotter, just warm to the touch. I guess with the deeper chassis in the CT5 things can cool better as there's more space for heat dissipation.

Similarly in the new ET series preamps, having that one tube inside / under the top cover manages the heat build up with ventilation slots. In the case of the GAT/S2, and other preamps, the tubes are housed externally so heat dissipates better I'm thinking...

I know one chap who's ET5 started burning tubes pretty quickly, had to change within 6 - 8 months. Then he upgraded to the GAT and the tubes require changing just within a year. So I'm not too sure about the 2-3 year mark as stated in the owners manual. As AJ mentioned, best to change tubes whenever you hear unwanted noises... time for fresh tubes and it sounds a whole lot better!

Having a single gain stage on preamps and power amplifiers and having these circuits directly coupled to the output stage does deliver a purer sound, without a doubt. I guess this design in simplicity comes with a small cost of changing tubes more frequently though.

I'm now starting to build up a few spares, at least two sets of each tube type. At times it does seem frustrating and I begin to think SS devices and their maintenance is much easier... however, whenever that tube is replaced and the tube gear gets going, that sound signature is just marvellous! So life goes on and tubes are glowing!

Cheers, and enjoy those fine tunes!
RJ

[Timo62]

It does seem odd that Conrad Johnson is only using one tube for some of their preamps. I understand the simplicity with just using one tube , but if it is hard on the single tube, it might be time to rethink the one tube approach. Especially considering if one prefers NOS tubes and the cost of these tubes.

[AnotherJohnson]

I think the problem is that they use a NOS tube at the factory.
The fresh 6922s seem to hold up better.

They will always choose the design that they believe sounds better.

Time will tell if they change their mind. Their decisions are not based on corner cutting.

Frankly, a lot of their customer base, and reviews, suggest that they’re getting a good result.