DC coupled cathode follower

[mikepukmel]

OK I get the main idea, not quite there yet on all of the theory.


The Valve Wizard

Aiken says, about adding this circuit after the phase inverter:

"This effectively isolates the output tube grid circuit from the phase inverter and its associated AC coupling, and provides a very low impedance source for the output stage. This will prevent the output stage from going into grid clamp, and will eliminate the long time constant of the AC coupling."

here:
What Is "Blocking" Distortion?

so, a really naive question: if the cathode follower is put between the phase inverter and output stage, won't you still need a coupling cap between the cathode follower and input grid of the output tubes?

Ive been searching for a production amp schematic that has a dc coupled cathoder follower between the phase inverter and output tubes, but haven't found one. Seems to be popular to put them in the preamp, before the tone stack, like the Marshall JTM45. But long tail pair phase inverters seem to mostly all dump their output right through a cap to the output tubes.

?

[mikepukmel]

Is this one?
http://www.thetubestore.com/lib/thet...-Schematic.pdf



Wow, how many tubes can you fit in one amplifier, anyway? When the dude switches this amp on, the street lights dim.
http://www.thetubestore.com/lib/thet...-Schematic.pdf

[Justin Thomas]

Wow, how many tubes can you fit in one amplifier, anyway? When the dude switches this amp on, the street lights dim.
[/QUOTE]

Ever heard one up close and in person, or better yet, played one on 7? All those tubes are worth it!

Justin

[g1]

Yes, the SVT is an example.

Wow, how many tubes can you fit in one amplifier, anyway?

At least this many. Twelve is just for the power amp, another 4 in the preamp.
Cathode follower drivers are not DC coupled though.
smyba300.pdf

[SoulFetish]

Is this one?
http://www.thetubestore.com/lib/thet...-Schematic.pdf

Yes, the SVT uses a cathode follower which is DC COUPLED to the output tubes. Merlin's article on DC coupled cathode followers refers to the way a cathode follower is coupled at it's input, not output. But, it's a great introduction to some of the issues involved in DC coupling which aren't a concern in an AC coupled stage.
You mentioned you had some uncertainty in understanding some of the theory behind this.
We'd be happy to go into some of the theory behind this approach, and shed some more light on cathode follower circuits. Try this: In your own words, try and explain the parts of the circuit that you understand. When you get to a something which raises questions, it us give us a picture of where your at and provide better answers. That way we're not rewriting Merlin's chapter on cathode followers or telling you something you already know. Of course, we love seeing schematics. Dont br shy about drawing them.

[mikepukmel]

Wow, how many tubes can you fit in one amplifier, anyway? When the dude switches this amp on, the street lights dim.

Ever heard one up close and in person, or better yet, played one on 7? All those tubes are worth it!

Justin[/QUOTE]

Oh man I would REALLY like to hear one of these!

[mikepukmel]

Yes, the SVT uses a cathode follower which is DC COUPLED to the output tubes. Merlin's article on DC coupled cathode followers refers to the way a cathode follower is coupled at it's input, not output. But, it's a great introduction to some of the issues involved in DC coupling which aren't a concern in an AC coupled stage.
You mentioned you had some uncertainty in understanding some of the theory behind this.
We'd be happy to go into some of the theory behind this approach, and shed some more light on cathode follower circuits. Try this: In your own words, try and explain the parts of the circuit that you understand. When you get to a something which raises questions, it us give us a picture of where your at and provide better answers. That way we're not rewriting Merlin's chapter on cathode followers or telling you something you already know. Of course, we love seeing schematics. Dont br shy about drawing them.

Thanks I will do that! This is cool stuff.

[mikepukmel]

Yes, the SVT is an example.

At least this many. Twelve is just for the power amp, another 4 in the preamp.
Cathode follower drivers are not DC coupled though.
[ATTACH]43196[/ATTACH]

that thing is the titanic of tube amplifiers. And its got a whole bunch of other stuff as well. The neighbors would love me!!