I shouldn't have said that for the IT-coupled driver: of course there is no current diversion in the IT case.
Instead, current diversion would apply to RC coupled stages, or current source loads.
Rod, thank you for answering my original question, very helpful. Please allow me to summarize to ensure I understand. The reason is as follows: higher current = more linear (less distortion) parts of the tube curves. Given that I have an IT coupled solution, there is roughly 1.8mA that needs to be subtracted from my existing operating point of 13mA. I changed the current to 13mA recently, so 13-1.8=11.2mA which is reflected in BLUE on the graph attached.
If we want to improve the distortion by moving to a more linear part of the curves, then the current could be moved to the ORANGE operating point by reducing the bias. This would require a new IT to support the increased current.
Sound correct?
If we want to improve the distortion by moving to a more linear part of the curves, then the current could be moved to the ORANGE operating point by reducing the bias. This would require a new IT to support the increased current.
Sound correct?
Attachments
The 1.8mA diverted current doesn't apply to the IT couped driver (I was too preoccupied thinking about slew rates to remember that IT stage is not the same as RC or CCS stages).
But more anode current in the 30A driver will give lower anode-resistance ra (important!) and better linearity, yes.
But the IT must not be operated beyond the DC current allowed in the specification.
But more anode current in the 30A driver will give lower anode-resistance ra (important!) and better linearity, yes.
But the IT must not be operated beyond the DC current allowed in the specification.
Pat,
Why not try parafeed output?
30A loading -appropriate- choke (or SS devices: CCS, gyrator), capacitor coupling Monolith IT.
Why not try parafeed output?
30A loading -appropriate- choke (or SS devices: CCS, gyrator), capacitor coupling Monolith IT.
Final update:
I recently purchased and implemented the 30A as a driver for the GM70. At first, I did not like the 30A as it was sterile and thin sounding. After about 100-150 hours, the 30A is singing nicely. This tube needs 100+ hours break-in before it starts to have a sweet, pure tone. That said, it is very revealing (top to bottom). The bias methodology (and related parts) are very audible. I am using Filament bias and tried several different resistors before I finally settled on the Duelund Cast 5ohm. I have a pair of Koolohm resistors that I will audition next week in the filament bias position. The 30A will show everything about the resistor.
Operating points (from memory): 440Vdc, -5V bias, 15mA.
I am currently using a 200H IT (nano crystalline from Monolith Magnetics). Contemplating a new IT with higher current capabilities.
Thanks to everyone for helping.
I recently purchased and implemented the 30A as a driver for the GM70. At first, I did not like the 30A as it was sterile and thin sounding. After about 100-150 hours, the 30A is singing nicely. This tube needs 100+ hours break-in before it starts to have a sweet, pure tone. That said, it is very revealing (top to bottom). The bias methodology (and related parts) are very audible. I am using Filament bias and tried several different resistors before I finally settled on the Duelund Cast 5ohm. I have a pair of Koolohm resistors that I will audition next week in the filament bias position. The 30A will show everything about the resistor.
Operating points (from memory): 440Vdc, -5V bias, 15mA.
I am currently using a 200H IT (nano crystalline from Monolith Magnetics). Contemplating a new IT with higher current capabilities.
Thanks to everyone for helping.
