Tube Watts Vs. Soild-State Watts?

Great call on the identity of the amp, Charles.

Based on its technical characteristics and on what I’ve heard about NAT products I too see no reason to doubt that it will work out well with the DIs. 333Jeffery, just be sure to keep in mind that there is probably something like 3,000 volts on the anode cap at the top of the power tube when it is powered up, and perhaps for some seconds or minutes after the amp is turned off! Although the blazing hot tube will no doubt eliminate any temptation to get near it during that time, anyway.

Also, given the high sensitivity of the DIs you may find the 30 watt low power mode the amp provides to be useful during the hot weather months. In their full power mode I suspect the two monoblocks will be consuming something like 800 watts of AC power, continuously, and converting nearly all of it into heat.

Good luck. Regards,
-- Al

I’ll have to go on Ebay and get some spare QB5/1750 tubes for it.

I see that some sellers on eBay are offering GU-46 tubes for relatively low prices, and are indicating that they are equivalent to the QB5/1750. However the GU-46 is specified as being usable up to a maximum anode voltage of 3000 volts, while the corresponding spec for the QB5/1750 is 5000 volts. There might also be other significant spec differences between the two tube types; I haven’t checked further. So I would suggest that you avoid the GU-46 unless you are able to obtain confirmation from NAT that it would be suitable for use in this amp.

Regards,
-- Al

Edit: For that matter, I see that the GU-46 and the QB5/1750 don’t even have the same number of pins in their bases. So the statements in some of the eBay listings for the GU-46 that it is similar to or equivalent to the QB5/1750 are definitely to be ignored.

Yes, current is what drives the loudspeaker, but all things being the same, a tube amplifier rated at say 50-watts will generally sound much louder than a SS amp at 50-watts.

I'm with Al  in regard to the output tube selection process, confirm with NAT  before even thinking about any possible tube alternatives.  This is a serious amplifier with ultra high voltage and I'm certain strict design criteria and circuit and power supply layout. Reviews and word of mouth say this is a superb sounding amplifier. I'd be surprised if it doesn't clearly outperform the Musical Fidelity transistor amplifier currently in use. Jeffery you may discover that you've achieved a world class audio system.  
Charles 

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