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12-08-2022, 02:21 PM
Hi Guys
The differences between OTs are many. If you try to narrow them down by taking samples from a single product line by a single manufacturer, even then you may not be making a "scientific" comparison, even if the same person designed every unit in the line. For example, Hammond has many OTs in the 1650-series, but these were designed by different engineers over a period of time, and then modified later by different engineers. Different techniques were used on different models.
The narrowing to given product line DOES give you a comparison of what is available, which in the end is what matters.
Because the tube has a nominally-set transconductance, the amount of current it wants to push through the OT is set for a given grid-1 voltage change given Vs and Va are stable. Changing the OT impedance means the effective voltage gain of the tube is different with each OT sample. Whatever fixed PA circuit you use, if it has feedback or not, the impact on how hard the circuit is driven or how it tries to accommodate the changed load varies.
Each OT design has its own parasitic elements and these impart distortions to the signal trying to pass through it. Combine this with the circuit adaptations above and you have a very unpredictable situation tone-wise. This means you cannot make a general statement, such as "going to high-z adds harmonics", which would be the intuitive notion. Higher turns ratios DO introduce stronger parasitic impacts in general, but it cannot be assumed to be a guarantee of tonal shift.
I know from talking with many techs and builders that for a given build where they have tried a range of primary values for OTs, that they can hear a difference and choose something specific for the build. This may sacrifice power, but amps are designed for tone. You may find the impact is greater in simpler circuits, particularly where other distortion mechanisms have been dealt with, particularly grounding and wiring.
You really have to try it for yourself.
The differences between OTs are many. If you try to narrow them down by taking samples from a single product line by a single manufacturer, even then you may not be making a "scientific" comparison, even if the same person designed every unit in the line. For example, Hammond has many OTs in the 1650-series, but these were designed by different engineers over a period of time, and then modified later by different engineers. Different techniques were used on different models.
The narrowing to given product line DOES give you a comparison of what is available, which in the end is what matters.
Because the tube has a nominally-set transconductance, the amount of current it wants to push through the OT is set for a given grid-1 voltage change given Vs and Va are stable. Changing the OT impedance means the effective voltage gain of the tube is different with each OT sample. Whatever fixed PA circuit you use, if it has feedback or not, the impact on how hard the circuit is driven or how it tries to accommodate the changed load varies.
Each OT design has its own parasitic elements and these impart distortions to the signal trying to pass through it. Combine this with the circuit adaptations above and you have a very unpredictable situation tone-wise. This means you cannot make a general statement, such as "going to high-z adds harmonics", which would be the intuitive notion. Higher turns ratios DO introduce stronger parasitic impacts in general, but it cannot be assumed to be a guarantee of tonal shift.
I know from talking with many techs and builders that for a given build where they have tried a range of primary values for OTs, that they can hear a difference and choose something specific for the build. This may sacrifice power, but amps are designed for tone. You may find the impact is greater in simpler circuits, particularly where other distortion mechanisms have been dealt with, particularly grounding and wiring.
You really have to try it for yourself.
