amp power & driver sensitivity in multiamp setup

PHY is a French manufacturer too...

'Taps' are the outputs of an output transformer. A tap is a connection into the winding of the transformer that allows for a different impedance. Usually a tube amp has an output for 4 and 8 ohms, possibly also 16. If there is only one output, its probably for 8 ohms.

The 1040 or 1050 seem the best bet in 6.5" drivers; the 2520 or 2530 in teh 8" drivers. Now I suspect that the specs are not accurate- they may be efficiency specs rather than sensitivity as claimed. The reason for this is that the drivers I have mentioned here have the same sensitivity rating while having two different impedances, and the sensitivity rating does depend on impedance somewhat.

What I am getting at is if these driver selection represent the same driver but in two different impedances, the 16 ohm unit should have had a sensitivity rating of 3 db less. Now they are claiming that the 16 versions are 100db, if that is really true the efficiency would 103 db.

This is because efficiency is 1 watt/1 meter regardless of the impedance, while efficiency is 2.83V/1 meter. 2.83volts into 8 ohms is 1 watt, into 16 ohms its only 1/2 watt- a 3 db difference. You might want to contact them and see if they can shed some light on this.

At any rate if the drivers are 100 db then you have a good chance of using them as midrange drivers with your 2A3 amp.

Thank you Ralph.

Let's assume for now the amp only has 8ohm taps (I've asked the manufacturer), and let's assume it's a stereo SET amp and one channel will be used to drive a 5 ohm tweeter (it measures 5 ohm flat across the usable bandwidth) and the other channel will be used to drive one of these midranges. Let's say the 16 ohm driver. Both drivers directly connected to the amp, with the crossover upstream from the amp.

Would you expect any downside in terms of sound performance or expected life of the amp by running different impedance loads on each channel?

Thanks again!

Yes.

In the case of driving a 5 ohm driver, the output of the amp will be lower power and higher distortion. Since its a tweeter, this might not be much of an issue as there is little power that is needed for a tweeter.

The 16 ohm load will also result in reduced power and more distortion, but the loss in power won't be as much as in the 5 ohm case. Also, the distortion will come from the output transformer and really not that much from the power tube; its the other way around in the 5 ohm case.

Since efficiency and power is a big deal in this case I would go with the 8 ohm version of the driver (assumed to be 100db 1 watt 1 meter) if you have a choice. This will keep distortion down and power up.

The life of the power tubes are likely not going to be much different in either case.