|Type 10 plate characteristics and loadline|
- Linearity of the constant current source is much better compared to resistive load line.
- Headroom or range has actually increased from just to -70V to infinity, or as high as your B+ is.
- Better gain is achieved.
- Power supply rejection ratio is improved as the tube is shielded by the constant current source.
- With the constant current draw, less demand is exerted on the power supply and therefore gives better sound!
- Tube is protected from over current due to being over driven.
- Bias is easily adjusted by a twist of screwdriver to tune for your taste.
- And many more
|Constant current sink & constant current source|
In above schematic, driver stage uses constant current source as load and power stage uses constant sink as cathode bias. On driver stage, you can use either the constant current source as load or constant current sink as cathode bias. In power stage, you can only use constant current sink as cathode bias in traditional single ended power stage with output transformer.
You can use constant current source as load too in power stage for parafeed topology, replacing the plate load choke. This is not common as too much power will be burnt in the constant current source circuit compared to a traditional plate load choke. Using just as cathode bias will bring enough benefits.
|Constant current sink for push-pull topology|
The most common device to be used (to us), is the LM317 or the IXYS transistor. We find that it is not as great as the discrete version but it is very convenient and easy to implement, not forgetting the accuracy and protection the LM317 has. We can't complain to much! There are plenty of constant current source and constant current sink designs in the internet. You can Google for it. We won't go into details here.