SUN AUDIO OF JAPAN
300B PUSH/PULL SCHEMATIC
The best wire cutter
ROCK AND ROLL TERRA INCOGNITA
My experience with these amplifiers compels me to assert that this topology is a "ROCK AND ROLL TERRA INCOGNITA" in America. This is, as yet, an unknown territory and it needs to be explored more.
15th Century Map of New Rock and Roll Territory
For most rock and rollers push/pull makes sense because this modality is relatively high powered. A push/pull 300B amplifier can produce between 25 and 50 watts per channel depending on how hard you drive the tubes. This means that many "normally moderate efficient speakers" can be used, though the higher the efficiency, the better all amplifiers will sound.
Let's review this unusual circuit.
Map of New Rock and Roll Territory- 21st Century
Notice that a 6SN7 is used with both halves of the tube connected in parallel. This has the benefit of lowering the impedance of the tube making it a better driver for the "single-ended" push/pull interstage transformer. The one problem with this "one voltage amp/driver tube" arrangement is its very low gain. The benefit is simplicity and it is directly coupled.
When you look at the transformer phase splitter and 6SN7, in effect, it looks like a single-ended amplifier on one side. You notice that one end of the phase splitter is connected to ground, and the other is connected to the plate of both halves of the 6SN7.
On the other side of the phase splitter, the side that drives the grids of the 300B is where we find the "push/pull".
You will also note that the plate voltage on the 300B is only 320 volts which is 100 volts below normal.
Let me explain the concept of this amplifier which explains its design eccentricities.
This amplifier was not designed for maximum power, but for maximum tonal quality. The combination of parallel "minimum" tube driver stage, direct coupling, single-ended transformer phase splitter, tube rectifier and "rich" operating point of the 300B is a strategy of refinement and it is successful.
The good news is that with the right speakers this modality kicks rock and roll butt in a major way, with a degree of refinement that only DHTs produce.
WHY IS THIS MODALITY NOT PRODUCED IN AMERICA?
I HAVE NOW TAKEN YOU ON A GUIDED TOUR OF AN AURAL TERRITORYTHAT IS TERRA INCOGNITA IN AMERICA,
YOU NOW KNOW WHAT CHRISTOPHER COLUMBUS FELT.
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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