The 45
Amplifier.
A two stage, ultrapathed, triode trick strapped WE 717a pentode driver with interstage coupling to an ultrapathed 45 tube single ended triode output stage.
After developing the Gran Sfera speaker a good, single ended triode amplifier to demonstrate them was needed. The 45 is my tube of choice though few loudspeakers are efficient enough for them. Anyone who says the 45 lacks bass or slam is probably referring to a lack in required efficiency. Revelatory bass resides in this tube as the Gran Sfera can attest. Since the Gran Sfera was developed for tubes such as the 45, a 45 amp was a natural for demonstration. Some well regarded amplifiers were about to be purchased when a quick inventory showed all the parts for an amp were in the bin including an unusual pentode tube slated for use in a DAC output stage. Distortion of these two types of tubes is complementary making an ideal driver and output combination. A breadboard with RC coupling was initiated. The 717a was setup as pentode as well as triode and both sounded good in their different ways. DRD topology was tried which was better than RC. Once the project was underway, the parts bin was discarded and better parts like interstage transformers were obtained. The driver experiments then began: from pentode operation to simple triode strap, diode strap, and finally the "triode trick strap" which sounded best. As many operating points were tried as possible, literally hundreds. Everything was dialled in that could be thought of and listened to, measurements finally laid aside. In this circuit, the 45 turned out to sound best on the classic point while 717a sweet spot was on its published voltage of both plate and screen with half the maximum dissipation.
AZZOLINA AUDIO SOUND MATTERS
A two stage, ultrapathed, triode trick strapped WE 717a pentode driver with interstage coupling to an ultrapathed 45 tube single ended triode output stage.
After developing the Gran Sfera speaker a good, single ended triode amplifier to demonstrate them was needed. The 45 is my tube of choice though few loudspeakers are efficient enough for them. Anyone who says the 45 lacks bass or slam is probably referring to a lack in required efficiency. Revelatory bass resides in this tube as the Gran Sfera can attest. Since the Gran Sfera was developed for tubes such as the 45, a 45 amp was a natural for demonstration. Some well regarded amplifiers were about to be purchased when a quick inventory showed all the parts for an amp were in the bin including an unusual pentode tube slated for use in a DAC output stage. Distortion of these two types of tubes is complementary making an ideal driver and output combination. A breadboard with RC coupling was initiated. The 717a was setup as pentode as well as triode and both sounded good in their different ways. DRD topology was tried which was better than RC. Once the project was underway, the parts bin was discarded and better parts like interstage transformers were obtained. The driver experiments then began: from pentode operation to simple triode strap, diode strap, and finally the "triode trick strap" which sounded best. As many operating points were tried as possible, literally hundreds. Everything was dialled in that could be thought of and listened to, measurements finally laid aside. In this circuit, the 45 turned out to sound best on the classic point while 717a sweet spot was on its published voltage of both plate and screen with half the maximum dissipation.
AZZOLINA AUDIO SOUND MATTERS