300b lovers

I was there. Thom’s amps did not use interstage coupling (at the time), so 8 watts is pretty much all she wrote. Frankly, I was kind of surprised ... I knew Thom’s NiWatts were maxed out for all they were worth, but audibility was surprisingly low. No flabby bass. No clipping as such, just really loud sound from an absurdly low-efficiency speaker. No screech, but not dull or muffled, either. A shocking amount of punch and bass slam. We both knew in advance that the combination of no feedback (thus no hard-clipping or saturation) and the split supply would protect the amp from things getting really out of hand.

Thom kind of did it on a dare, trying to get the fuse to blow. We both wanted to hear what the NiWatts, still in rough prototype form, did when given an impossible situation. The split power supply really, really came through. The 300B was getting hammered while the rest of the amp just sailed right through. It acts like an 8-watt compressor with surprisingly subtle action.

It reminded me of a little practice guitar amp, which if you have heard one, can get insanely loud, and retain its basic character.

P.S. Yes, Karna Mk II, or Statements, have independent regulated B+ supplies for input+driver and output section, with massive overdrive capabilities. That’s something the Mark I’s, the Statements, and the NiWatts all share. It makes them sound many times more powerful than the nominal wattage rating would suggest. Surprisingly, the 300B survives this gross abuse with no apparent damage, not something I expected.

@lynn_olson

 Surprisingly, the 300B survives this gross abuse with no apparent damage, not something I expected.

Well as you said earlier,

Bell Laboratory and Western Electric knew what they were doing.

90 years later and it's still very much admired, appreciated and enjoyed by discerning music lovers. Quite the testament.

Charles

As Lynn said, the amps have dual regulated supplies, one for the 300b and one for the input and driver tubes.   IF the specs on that KEF speaker above are really what the review said, then the amp would drive them.   Also, as I said far above somewhere, the first stereo prototype of this circuit with only one power supply per channel drove a pair of experimental Spatial Audio Labs X4 prototype speakers that were approximately 87 dB 4 ohm to insane levels, much as what Thom was describing above.  The monos have dual supplies in each amp, so would be even more capable.  All that said, I would stick to speakers that are 88+ dB and very well behaved.  The spatial audio X4 current model is 88 dB 4 ohm (and very well behaved) and the amps will happily drive them to ear splitting levels in reasonable room.

@donsachs

I would stick to speakers that are 88+ dB and very well behaved. The spatial audio X4 current model is 88 dB 4 ohm (and very well behaved) and the amps will happily drive them to ear splitting levels in reasonable room

As @atmasphere has made the point eloquently on past occasions, easy load impedance (Higher ohms and less fluctuations ) speakers are less stressful on amplifiers. In addition he has pointed out that they are lower in distortion compared with low impedance speakers.

Charles

You don't have to convince me, my speakers are 97 dB 8 ohm:)

I wouldn't own an inefficient speaker because I would be doomed to SS amps, and I hate the sound of solid state devices.