cathode follower with gain

[trancy]

can someone show me, how to build mu CF with ECC88, power supply +/- 50 V or 100V, with gain 3, input res on my amp is 4,7Kohm (3,5V ,700uA)...

thanks

 

[fscarpa58]

Hi trancy

A CF alone has no gain ( gain <1).
It has to be preceded (or followed) by a gain stage.

Federico

 

[trancy]

Hi trancy

A CF alone has no gain ( gain <1).
It has to be preceded (or followed) by a gain stage.

Federico

yeah ....like that...

I was trying to make a schematic in micro-cap, but probably Im too stupid.....

 

[fscarpa58]

Hi trancy

Last year I was in Bled for my white week holidays
Beautiful place.

I'll send you a pic for a 6dj8 common cathode
followed by a CF.
But since a gain of 3 is very low I have to
attenuate the input or the output.

Federico

 

[Sch3mat1c]

A mu stage has a CCS-loaded triode (although it should work with pentodes just as well) with CF output. Think about it!

Tim

 

[JojoD818]

Trancy,

Attached is a cathode follower followed by a common cathode stage. I was told that tubes such as 6DJ8, 6922, ECC88, 6N1P can be used for such a configuration.

Federico,

Would it be possible for you to provide values for the resistors using 6N1P and ECC88 tubes? I have a couple of 6N1P sitting here waiting to be used.

Thanks!

JojoD

 

[trancy]

Hi trancy

Last year I was in Bled for my white week holidays
Beautiful place.

I'll send you a pic for a 6dj8 common cathode
followed by a CF.
But since a gain of 3 is very low I have to
attenuate the input or the output.

Federico

wau...I live near by Bled, next time we should meet...


Iam waiting for your sch. .....thanks a lot...

 

[fscarpa58]

Hi trancy

Sorry for the delay, but yesterday
I had not success in connecting
to the forum.
here is the pic

ciao

Federico

 

[fscarpa58]

JojoD

what is the input resistance of the amplifier?
( I am supposing that this is a preamplifer
which will drive an amplifier)

ciao
Federico

 

[trancy]

thanks a lot federico, I will report how it works soon...I hope without smoking signals....

 

[fscarpa58]

trancy, I forgot

You have to put the volume pot in front of it,
obviously.

reference curves at

http://www.audiomatica.com/tubes/6dj8.htm

Federico

 

[JojoD818]

JojoD

what is the input resistance of the amplifier?
( I am supposing that this is a preamplifer
which will drive an amplifier)

ciao
Federico

My Leach amp input resistance is 20K ohms. I would like to use a 100K pot but 50K, 250K, 500K are also available. My tubes are 6N1P. Available B+ is 150V @ 100mA regulated.

Please, Thanks!
JojoD

 

[fscarpa58]

JojoD

B+ 150 V is very low for the 6N1P.
However, I'll try something.

see you later

Federico

P.S. I wiil use the duncan model. If you prefer
something different send it to me.

 

[JojoD818]

JojoD

B+ 150 V is very low for the 6N1P.
However, I'll try something.

see you later

Federico

P.S. I wiil use the duncan model. If you prefer
something different send it to me.

Federico,

That is the psu I already have setup, duncan model is fine with me. I would love a unity gain but if not possible, your smallest gain design would be fine.

Thank you very much!

JojoD

P.S. Already have ceramic tube sockets, will look for suitable aluminum casing tomorrow. Will be waiting...

 

[fscarpa58]

Excuse me, jojod

but if you want a unit gain cir then
schematic in post #6 is not good.
you need a simple CF.

Federico

 

[fscarpa58]

However

this has about 25 db of gain.

I really do not like it.

 

[fscarpa58]

this has a gain of -0.5 db (about 0.95)

and, in my opinion, it is better
( if you don't need gain)

bye
federico

 

[fscarpa58]

however

if you can have your supply to float,
I strongly recommend the following.
better PSRR, smaller caps.

bye

 

[JojoD818]

Federico,

First of all, thank you very much for your time!

May I ask why you don't like the one with a 25db gain? I ask because I am really interested in that topology. BTW, those resistors are 2W right?

Regards,
JojoD

 

[fscarpa58]

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