Attempt to clone famous designer

[zonula]

Hi everyone,

This is my first post on DIY group. I'd like to know what you think of my schematic.




I spent several hours figuring values and global topology (yet I am sure there is non sense nodes in the picture I am posting). Anyways, I managed to have the "target" 8v peak-to-peak reported by Art Dudley in sterephile at the output transformer.

I would really like to replicate and build this circuit. I have many more files I can share.

I feel really excited and serious about this new project.

Thanks in advance,

Olivier

 

[abbey road d enfer]

There are several dubious things. First, why use a triode-connected tetrode for the input?
Now I fail to understand R8/C1.
And the output tetrode's screen is floating...? And the cathode-follower connection seems weird...with the grid more positive than the cathode.
Can you post your .asc file AND the models AND symbols for the tubes?
The way the reference for the voltage-follower is bootsrapped by the input tube's cathode seems strange. It may be part of the original design's mojo, though.
BTW, LTspice doesn't like floating nodes such as those of the xfmr's secondary.
Just a 1 Gohm resistor to ground will help.

 

[zonula]

There are several dubious things. First, why use a triode-connected tetrode for the input?
Now I fail to understand R8/C1.
And the output tetrode's screen is floating...? And the cathode-follower connection seems weird...with the grid more positive than the cathode.
Can you post your .asc file AND the models AND symbols for the tubes?
The way the reference for the voltage-follower is bootsrapped by the input tube's cathode seems strange. It may be part of the original design's mojo, though.
BTW, LTspice doesn't like floating nodes such as those of the xfmr's secondary.
Just a 1 Gohm resistor to ground will help.

Thank you @abbey road d enfer for the constructive reply

Yes some weird cathode follower connection. Thank you for the floating node on the xfrm secondary. Here are my ASC and LIB. The way my pentode model work is based on a tetrode model (see lib file)

For the R8/C1, the is a bit of guessing. The company making these film (I suppose) capacitor is Nissei (http://en.new-nissei.com/productDetail.aspx?proid=67)

 

[abbey road d enfer]

Without DC voltage on the screen, the final tetrode runs at sub-uA current, so has no gain and no drive capability.

 

[ruffrecords]

The first stage looks like an SRPP but the function of R8 and C1 is obscure.
The output stage clearly attempts to bring negative feedback to the bottom cathode of the SRPP but again the mechanism is obscure.
And as Addey says, the screen grid of the output tube does need some dc on it.

Do you have a schematic of the original?

Cheers

Ian

 

[zonula]

Yes R8 and C1 are obscure! My drawing are based on pictures of the interior of the amp as no schematics are available...

Thanks for @ruffrecords and @abbey road d enfer for the comment about DC on the the screen of the final tetrode.

Here is another view of the connections

 

[abbey road d enfer]

One problem is that C3M is a pentode (and the input tube also). Actually designed to operate with Vg3=0, but Vg2 must be high (60-150v).
The tetrode model you use in your sim is incompatible with that.

 

[zonula]

Thanks! @abbey road d enfer I'll look for a better way to simulate