tubes and current

Thanks for the suggestions so far.

Don't change the amp change your speakers

Your speakers and your amp are just about as polar opposite as one could get when trying to match an amp with a pair of speakers. You can read up on tube circuits, current delivery, current vs. voltage source amps, etc., etc., but the bottom line is you need to decide do you want to keep the amp or the speakers. If you decide to keep the speakers, you'll need to make a significant investment to get a tube amplifier that could drive them to their full potential. Or you could make a fraction of that investment and get a solid state amplifier that would give you all you need minus the tube "flavor". If you decide to keep the amp, look for speakers with efficiency/sensitivity of >96dB, full-range single driver or otherwise, and you'll be very happy with the results, assuming you like that sort of sound. Hope this helped.

Great suggestions by Pdreher!

Given that your speakers have presumably been designed with the expectation that they would typically be used with solid state amps, and given their very widely fluctuating impedance curve (see Figure 1 of Stereophile’s measurements), what you need in addition to adequate power is low output impedance. "Low" for a tube amp, that is.

Nearly all solid state amps have very low output impedance. Tube amp output impedances vary widely among different designs. SETs tend to have relatively high output impedances, and the interaction of a high output impedance with the impedance variations of your speaker will result (relative to the tonality that would result with a solid state amp) in under-emphasis of frequencies at which the speaker impedance is low and over-emphasis of frequencies at which the speaker impedance is high. Which in this case would appear to mean an over-emphasis of the upper mid-range and an under-emphasis of the bass, part of the lower mid-range, and the upper treble. Which doesn’t seem to coincide with the "lush and full bodied" sonics you indicated you are looking for.

The VAC Renaissance 30/30 provides a 2 ohm output tap as well as 4 and 8 ohm taps. The 2 ohm tap will provide lower output impedance than the others. The amp also provides adjustable feedback, which will give you a lot of flexibility in optimizing tonality. More feedback = lower output impedance, but might trade off against the intrinsic sonic character of the amp to some degree. Also, the fact that the amp is very heavy speaks well of the robustness of its power supply and its ability to deliver current.

In term of power capability, I suspect that its 32 watt capability in combination with your 88 db speakers will be adequate for the vast majority of classical orchestral recordings. There may be a few having exceptionally wide dynamic range, though, such as some of the older Telarc and Sheffield Labs recordings, which will have brief dynamic peaks that it may not be able to handle.

The more powerful Music Reference amp Pdreher referred to is also highly regarded. That and other Music Reference amps with which I am familiar have output impedances that are considerably lower than average for a tube amp, as can be seen from their specified damping factors (damping factor being inversely proportional to output impedance). Also, Stereophile measured an output impedance of only 0.3 ohms for the original version of the RM-9.

I have no particular knowledge of the Quicksilver amp that was suggested, and in particular what its output impedance or damping factor may be.

Hope to clarify here my original question is ’does adding more tubes increase high current of amp (not just watts) or is high current mainly determined by amp design and transformer used and not directly related to amount of tubes used’.

There are a great many design-dependent variables which affect how much current an amp can deliver. However, most amps which provide a 4 ohm or lower output tap and can provide adequate power capability for your needs will be able to deliver adequate current. What is more important, given adequate power capability and good quality design, is a suitable match between amplifier output impedance and the variations of the speaker’s impedance over the frequency range.

Good luck. Regards,

-- Al