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Speaker load on tube amplifier...

Hello A'goners,

I have a used (two month old) Dennis Had fire-bottle arriving in a few days. I understand it works with a wide variety of tubes. It has been suggested that I go with KT-88's. This is my first serious tube product and I want to make sure I'm not doing damage when I hook my 4ohm speakers (3.1ohm dips) to the amp. The amp comes with the Golden Lion KT-88's and the 7581's by Tung Sol. Because of the impedance dip of the speaker, the KT-88's were recommended. Why is this the case? Why not 7581's? Which tubes are best for 4ohm nominal speakers and why is this the case? 

Thank you,
listening99

Showing 1 response by freediver

freediver
1,309 posts
 
I’m no Engineer so I will not try to explain the why but recently I have been experimenting between EL-34 & KT88 tubes in my amplifier(can use either),switching also between Triode & Ultralinear modes..To my ears the KT88 has a more extended treble,every bit as good a midrange as the 34’s & Bass is no contest,34’s sounding loose compared to the 88’s...
Also it is NOT the tube,it is the POWER TRANSFORMERS that dictate how hard a speaker it can drive..
As for the speakers it is not only how far down the impedance dips but also how the Phase of the signal matches.An impedance balanced speaker may dip to 3 ohms but with a smooth phase relationship does not tax the amp..Found this on the net,looks like it will drive real speakers but if it only has 8-10wpc.they better be at least 88db.sensitive or you won’t get much undistorted volume...
PURE CLASS A, TRIODE,2 WATT TO 8 WATT OUTPUT WITH VARIOUS OUTPUT TUBES,FIVE SECTION DC POWER SUPPLY WITH DUAL FILTER CHOKES,REGULATED DC, B+ VOLTAGE ON DRIVER TUBE,REGULATED DC POSITIVE CATHODE BIAS ON DRIVER TUBE,PURE VACUUM TUBE RECTIFICATION-DUAL PI-NETWORK FILTERING,AUTO-BIAS FOR PLUG AND PLAY TUBE ROLLING
DESIGNED TO DRIVE REAL WORLD LOUDSPEAKERS IN THE 90 dB SPL RANGE OR BETTER AT 2 OHMS TO 20 OHM IMPEDANCE...
IMO your going to need seriously sensitive speakers to get the best from this amp...

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