Andy Evans wrote:

In that case, if there is a tap on the OPT to give a load match to 3
ohms, the Rout without NFB will be 1 ohm, and loads below 4ohms nominal
will be tolerated OK.

The impedence of the speakers is around 3 ohms. So as you say you
figure for a low ohm tap on the secondary. I'm getting good sound with
a PPP 6S4A amp with a nominal 8k a-a into 4 ohms, which works out just
about OK. Sounds fine. My brother uses a Nagra VPA 845 PP valve amp,
which sounds great. A friend uses a KT88 amp with feedback. That works
too. All of us have Caliper Sigs, though my friend just upgraded to
Duettas. Drool.


25Watts class AB1 is easy from 300B and if speaker sensitivity is above
88dB/W/M, sound is OK but the higher the sensitivity the better.

Apogees are what, about 85db - something like that.


With 85dB its getting a bit hard to drive and I'd like to have 50W
available....

What's so great about ribbons though?

Have you heard the big Apogees? They're now built down under.
http://www.apogeeacoustics.com/index.html

I wasn't aware of that.

There is another ribbon company, Ambience on the sth coast NSW.

Are you anywhere near Queensland's "sunshine coast"?

No, I'm in Canberra, 300km sthwest of Sydney.

I prefer really well done dynamic cones and domes.

Patrick Turner.

Andy