Tube Amp Questions

Hello all!

I've decided to build my system around my Thiel CS 3.7 speakers. Currently, I'm using an ARC LS-7 tube line-stage (purchased just 3 weeks ago) feeding my old Denon PMA-2000 IVR integrated. Sources are laptop running Tidal & Roon, as well as Denon 2900 CD/SACD player.  Musical tastes are varied, but I listen mostly to classic rock, the blues, classic jazz & Latin/bossanova. 

My questions are regarding tube amps. One, in real-world experience, are they really that labor intensive to maintain & operate?  Two, the particular amp im considering is an ARC VS110. According to ARC, it draws 400 watts at idle, 620 at rated output & 900 maximum. How big of an impact does running an amp like this have on an electric bill? 

These are newbie questions, I know, but after a really long time as an admirer of the "High-End", I've finally decided to leave "Mid-Fi" behind, albeit by going the vintage/pre-owned route. 

Thanks for any input or reccomendations!


I, too, am new to tubes. I went with Atma-Sphere, and am super happy with my choice. 
The ARC is no slouch and would probably sound better with a better amp (tube or SS). IMHO.
I would PM Ralph Karsten (atmasphere) and get his opinion/knowledge.

I have a VT100 which is similar in size to the VS110 as far as output tube complement (8 6550 output tubes). They do generate a lot of heat and need some open space for cooling. If you're going to run it 8 hours a day you'll notice it on your bill. 8 hours a week who cares.

For the most part they are plug and play but they do need some occasional interaction. You'll need to check tube bias occasionally and every few years replace the tubes depending on how often you run it.

If you're of a mind to get a European sports car get a tube amp. You can tinker on occasion but it won't leave oil spots on the floor. And you can get years of enjoyment and pride.

If you're more a sedan type guy I'd look at something more solid state. A little more reliable and almost no maintenance. Nothing wrong with mixing a tube pre with a mosfet power amp.

As far as tube preamps are concerned there's not much maintenance until the tubes start to wear out and that can be years. Replacement is easy.
My suspicion is that the VS110, as well as many other tube amps, would be a poor match for the Thiel CS3.7. From Stereophile’s measurements of the speaker:
...the CS3.7’s impedance remains between 2 and 3 ohms over much of the audioband (fig.1), and that there is a demanding combination of 3.8 ohms and –40° capacitive phase angle at 60Hz. Thiel specifies the impedance being nominally 4 ohms, with a minimum of 2.8 ohms. I actually found the minimum impedance to be 2.4 ohms at 125Hz. The difference between 2.8 and 2.4 ohms is academic, either mandating use of an amplifier that has no problem delivering high currents.
Figure 1 at that link, which depicts the speaker’s impedance magnitude and phase graphically, further reinforces my belief that the CS3.7 is not a tube-friendly speaker.

Also, as stated in Stereophile’s measurements of the VS110:
The output impedance from the 4 ohm tap was a fairly high 0.72 ohm across most of the audioband, this rising to 1.3 ohms at 20kHz. The equivalent figures from the 8 ohm tap were 0.93 ohm and 1.9 ohms, respectively. As a result, the modification of the amplifier’s frequency response due to the Ohm’s Law interaction between its output impedance and the way in which a speaker’s impedance changes with frequency will be quite large.
So IMO, generally speaking, a solid state amp would stand a much greater chance of being an optimal match for that speaker. Although in choosing one keep in mind that its input impedance should conform to ARC's load recommendation for the LS7:
Recommended load 60K ohms and 100pF (20K ohms minimum and 1000pF maximum)
(The pF part won’t usually be a problem, unless the interconnect cables are unusually long. But many and probably most solid state amps will have input impedances below 60K ohms, although I wouldn’t worry about it if the input impedance is around 30K or more).

It may be worthwhile for you to search Audiogon’s "Virtual Systems" section to see what amplifiers others are using with the CS3.7 or similar Thiel speakers.

Good luck. Regards,
-- Al

almarg +1. Thiels love SS amps. The tube pre is O.K.
Speaking as a former Thiel owner (1.6 an 2.4SE).
150 wpc minimum.