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cathode follower with gain

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#21
fscarpa58 said:
2W for 20k e 30k res

for the other ( 200, 1meg, 270k) also 0.2 W.

I like the topology very much but, in this case,
and with 6N1P, we need 300 V to have it working properly.

Owing to the constrain due to the rigid connection
between plate of 1th tube and grid of the 2nd, the working
point is not very good, that is high distortion
( 0.4% at 5Vrms out) and not very great max swing.

However it works and maybe you will like its
sound.


If you don't need gain the CF is advisable.

Federico
Click to expand...

Thanks Federico! Will give you updates soon.
 
#22
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
 
#24
Hi trancy

You have to decide.

post #16 is addressed to JojoD.
The cir has high gain, 150 V B+ supply,
it is tuned for 20k load, and uses 6n1p.

I post a message for you a few days ago.
It was a 3db gain with 100V B+, uses 6DJ8/Ecc88
and was tuned for 4.7k load.

let me know.

Federico
 
#26
fscarpa58 said:
Hi trancy

You have to decide.

post #16 is addressed to JojoD.
The cir has high gain, 150 V B+ supply,
it is tuned for 20k load, and uses 6n1p.

I post a message for you a few days ago.
It was a 3db gain with 100V B+, uses 6DJ8/Ecc88
and was tuned for 4.7k load.

let me know.

Federico
Click to expand...

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....
 
#27
Trancy

I really dont want to bother you federico
Click to expand...

I am happy to help you.

But I need clear data to work on.

1) type of circuit
2) tube
3) gain
4) B+
5) load

If you only want that I recalculate values for circuit of
post #8, here is the pic.

Federico
 

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#33
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
 
#35
fscarpa58 said:
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
Click to expand...

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?
 
#39
fscarpa58 said:
Trancy



I am happy to help you.

But I need clear data to work on.

1) type of circuit
2) tube
3) gain
4) B+
5) load


Federico
Click to expand...

hello

could you please....you know what.....help me....with recalculation....

1. circuit is attached
2. tube is ecc88 by siemens
3. more than 3
4. 100V
5. 4k7

correct me if I'm wrong: gain of tube is defined by u (for ecc88=33) and plate resistor (Rp)


thanx
 

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#40
Hi,

Do you really need to drive a 4K7 load?

The Zout of the anode follower using a ECC88/6DJ8 is probably going to be around that figure.

Ideally you should have a Zout of about 10 x lower than the Zin you need to drive.

Cheers,😉
 
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