Federico,
I agree with your comment about the poor operating point of the direct coupled CF. It does not sound so good.
However, the configuration has a huge advantage.
If the output is taken from the plate of the first tube, not from the cathode of the second, and if the plate resistor is made equal to the cathode resistor, then we have perfect current balance as long as the plate is held at half B+.
This means that the current draw of the two triodes will add to a constant; viz, perfect current balance. This makes power supply design very easy, and improves the bass performance a great deal because there is no voltage sag on the B+.
In 1999, John Broskie of Tubecad.com came up with this approach; I think it is very clever.
Cheers,
Hugh
I agree with your comment about the poor operating point of the direct coupled CF. It does not sound so good.
However, the configuration has a huge advantage.
If the output is taken from the plate of the first tube, not from the cathode of the second, and if the plate resistor is made equal to the cathode resistor, then we have perfect current balance as long as the plate is held at half B+.
This means that the current draw of the two triodes will add to a constant; viz, perfect current balance. This makes power supply design very easy, and improves the bass performance a great deal because there is no voltage sag on the B+.
In 1999, John Broskie of Tubecad.com came up with this approach; I think it is very clever.
Cheers,
Hugh
fscarpa58 said:
sorry for inconvenience federico,
I"ll try to make CF on 100V B+ with ECC88 from your schematic, and also I want to try on 150V B+ with same sch.(if I"m correct, higher B+ is better for sound quality)...
........
is there any simple formula to recalculate values, or its nessesary to have some tube related sw?
I really dont want to bother you federico, but...you know....I dont know anything about tubes...this is my first one....practicly I am a tube virgin....ohhhhh yeaaahhh....
hi
try disconnecting the heater while the
cir is on. usually it takes a few seconds
to go off due to thermal inertia.
See if during that time something changes.
Then, with cir on, try to move your fingers
near various part of the cir and see when
the hum increase further. Also touch
the cir. if you find some critical point
try to change layout there or use shielded
cable there. change ground path.
Try with cir in and outside the box if
you use one.
Federico
try disconnecting the heater while the
cir is on. usually it takes a few seconds
to go off due to thermal inertia.
See if during that time something changes.
Then, with cir on, try to move your fingers
near various part of the cir and see when
the hum increase further. Also touch
the cir. if you find some critical point
try to change layout there or use shielded
cable there. change ground path.
Try with cir in and outside the box if
you use one.
Federico
fscarpa58 said:
cir???? something new for me
I connect ground of heater (minus) on ground (is that o.k.?), and hum was half lower , after that i noticed, that when I touch speaker connector with osciloscope ground, its almost o.k. ????? power stage is dead quiet, when I disconect mu cf. Today I will try to change position of ground point, or maybe there is some other suggestions?
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