Adding tubes to SS system-Tube Preamp Amp or Int?

Ok. Then what is considered a 'benign' impedance? Also, are there any other general rules I should be aware of? What about the sensitivity of the speakers vs the power of the tube amplifier?

I know there wont be any 'absolute' rules. But how about some places to start for someone that really doesnt know much about it.

Wow! Thanks everyone for the comments, and it is obvious to me that I have lots to learn! Some of what you are saying I understand, some things I am not entirely clear on.

Looks like opinions pretty much cover all the options. I suspected as much really, but it is still somewhat overwhelming. However, it does seem that there is more of a preference for tubes in the power amp for the fullest 'effect'.

I hadn't thought much about tubes in the source components, DACs, or 'buffers'. I'm not convinced I want to go that route yet. But it is early on still and things may change.

Honestly, my idea of tubes in the preamp was driven mainly by it's perceived simplicity in connections. Seems like I could simply add a tube preamp to the system and connect it to my JC2 preamp via the bypass input, which would send the signal passed the JC2 untouched directly to the amp. I wouldnt need to switch around any speaker cables since I would have only the single SS amp. Any sources I wanted to hear via tubes could be connected to the tube preamp, and any sources I wanted to hear via SS could be connected to the JC2. However, in practice, I suspect I would still be switching the source cables back and forth as I would probably experiment with any single source with both preamps.

If I go the route of the tube amp instead, I am now thinking about components such as the Cayin integrated amps (A88T, A100T) which could be used as a standalone all-tube preamp/amp, while at the same time it is able to be used solely as a power amp using the preamp inputs it has that bypass it's preamp section. So I would have an all-tube integrated, with an option to be used as a tube power amp only. Is this a norm for tube integrated amps? Are there others like this?

So I have to ask a few more questions about the method of connection if I use a tube amp. The JC2 preamp has 4 pairs of outputs (balanced, unbalanced, etc) that are all active simultaneously. So could I connect the JC2 out to the SS amp via one output and to the tube (integrated) power amp via another output? I would have to switch speaker connections between the 2 amps dependent on which I wanted to use? How would this work out?

Yes, I deliberately left out the part about the speakers, although I am aware that it is a very important part of the equation. The reason for this is that I plan to upgrade speakers soon. Right now, I am using 20+ year old Vandersteen 2Ce speakers. And I am still unsure of which speakers I will be getting. I'm not sure whether to even bring it up here as I dont want this to turn into a discussion of speakers. But I realize it is important, so some of the contenders for new speakers would be: Dali Helicon 800, Monitor Audio PL300, Focal 1037Be, B&W 803D, Vandersteen Quatros or Model 5.

If I go the route of the tube amp, could someone explain in a bit more simplistic terms what I need to look for in order for it to match with the JC2 preamp and whatever speakers I eventually choose?

Larryi and Mapman-

Thanks for that info. More things slowly starting to make sense here. I'd like to go over a couple of specific examples if possible to explain further.

I should just start with my current speakers - the Vandersteen 2Ce. Specifications pulled from the manufacturers website (http://www.vandersteen.com/2cesigii_specifications.pdf) show the following:

IMPEDANCE: 7 ohms nominal 4 ohms minimum.
SENSITIVITY: 86dB with 2.83 volts of pink noise input at 1
meter on axis.
RECOMMENDED AMPLIFICATION: 40 to 160 watts per channel into 8 ohms.
FREQUENCY RESPONSE:
29Hz to 29kHz 3dB
32Hz to 21kHz 1.5dB
By FFT step function.
DISPERSION: 29Hz to 16kHz 3dB 30 degrees off axis.

The first page of the Stereophile measurements (http://stereophile.com/content/vandersteen-audio-2ce-loudspeaker-sidebar-3-measurements) show the graph I believe you are referring to. I cant say I understand everything completely here. But I think the set of curves that is generally lower might be the impedance since it tends to stick around 6 or 7 and then falls to around 4. Both sets of curves fluctuate wildly at the lowest frequencies, and then stabilize somewhat before gradually drifting up (phase) or down (impedance). I hope I got that much right. But other than that I cant say much about anything that would need to be addressed in terms of the amp needed to power these. As you say, the reviewer does indicate that this would be an easy speaker to drive.

Now on to the Dali Helicon 800 since this is one of my top choices for a replacement pair. Manufacturers website (http://dali-speakers.com/display_content.php/USA/speakers.html/179/1061) indicates the following:

Frequency range (+/- 3dB) [Hz]: 31 - 27,000
Sensitivity (2,83 V/1 m) [dB]: 89.5
Nominal impedance [ohms]: 4
Maximum SPL [dB]: 113
Recommended amplifier power [W]: 50 - 400

I unfortunately cant find the Helicon 800 impedance graphs. But just to use the Dali Helicon 400 review from Stereophile instead (http://stereophile.com/content/dali-helicon-400-mk2-loudspeaker-measurements) There may or may not be much correlation between these 2. But the impedance fluctuates wildly again at the lowest frequencies and then stabilizes and drifts between 4 and 6 or so. The reviewer again says they are easy to drive. Anything else to note?

And now Monitor Audio PL300. Again from the manufacturers website (http://www.monitoraudiousa.com/products/platinum/pl300/specification):

Frequency Response: 28 Hz - 100 KHz
Sensitivity (1W@1M): 90 dB
Nominal Impedance: 4 Ohms
Maximum S.P.L(Per pair in room): 118.6 dBA
Power Handling (RMS): 300 W
Recommended Amplifier Requirements (RMS): 100 - 300 W

Again no graphs at Stereophile, but for the PL200 (http://stereophile.com/content/monitor-audio-platinum-pl200-loudspeaker-measurements) the impedance fluctuates MUCH MORE throughout the frequency range. But also with a VERY high sensitivity. I dont know how this would differ in terms of the tube amp you might want to choose?

I just want to use these examples for the sake of discussion about what sort of ratings in a tube amp you might want with my current speakers and some of my options for new ones. I can go through several other speakers on my own to see how they compare as well.

And so far, my favorite contender for an integrated tube amp is something like the Cayin A100T. Mainly because I like the option it has of using the full integrated tube amp vs using the pre-in input terminals on this component, that would allow me to use this as a stand-alone power-amp with my Parasound JC2 as the pre. And for the sake of completeness, the specs on the Cayin are as follows:

Frequency response: 10Hz - 65kHz
Total harmonic distortion (THD): 1% (1kHz)
Signal-to-noise ratio: 89dB
Input Impedance: > 100 Kohm (RCA)
Vacuum tube: KT88 × 8, 12AU7 × 2, 6CG7 × 2, 12AX7 × 1
Input Terminals: Aux, Tuner, CD, pre-in
Circiut: Class AB PP
Sensitivity: 480mV, 900mV (pre in)
Output Impedance: 4 Ohm, 8 Ohm
Power Output: 50w Triode - 100w Ultralinear
Consumption: 280 W

I know this is a lot of reading. Thanks for following along and helping me out here. :)

Thanks again guys. I am understanding the graphs much better now.

My question now is concerning both of your comments that the impedance and phase shift graphs or specs I choose as examples are maybe not "tube gear friendly speakers". I understand what you are saying about only using the measurements and numbers as guidance and not the end-all answer, but if you see things in the graphs or specs that specifically lead you to believe this, I'm interested in what it is. In at least 2 of those 3 examples, the reviewer actually commented the the speaker would be an easy load to drive. So if there are things that are not tube-friendly, I'd like to know more about it.

Larryi- Thanks for the mention of the Prima Luna. That looks like another nice piece of equipment. And it also has an HT bypass that looks like it would give me the same option of using my SS preamp with just the tube amp in the circuitry. The only concern is for roughly the same price point the Cayin A100T has alsot double the power, uses similar tubes (but more of them) and had many of the same functions (although the Prima Luna has an auto-biasing) function that the Cayin does not). I was looking at the Ayon earlier this week, and it looks excellent too. There dont seem to be many reviews online though.

Mapman- Could you also offer a little bit of info about tube maintenance. It is one thing I have not considered at all yet. Approximately how often will the power amp tubes need replacing (roughly speaking)? What is an approximate cost for similar tubes? If one tube goes out, do thay all need to be replaced? Thanks again.