Self-split - can someone explain this to me ?

[KT66]

Hey gang, I have a potential customer that wants me to build him a harp amp with a "self split" output section topology. The schem he sent me ( attached) is a bit of a mystery to me, the grid of one of the output tubes is connected to ground, can someone explain the theory of this to me ?

[martin manning]

In short, the side with the grounded grid is driven through its cathode. At zero signal, both grids are at zero volts and both cathodes are at some positive voltage due to the current flowing through the common cathode resistor. A positive signal voltage from the preamp causes the current on that side to increase, which increases the voltage at the top of the cathode resistor. On the opposite side, this is seen as the grid becoming more negative with respect to the cathode, which produces a decrease in current flow. A negative signal voltage from the preamp produces the opposite effect. This scheme will have to operate in class-A to get an un-clipped signal at the speaker.

[WiderGates]

Hey gang, I have a potential customer that wants me to build him a harp amp with a "self split" output section topology. The schem he sent me ( attached) is a bit of a mystery to me, the grid of one of the output tubes is connected to ground, can someone explain the theory of this to me ?

Hello Ryan,

a link with a description how this works exactly, but it's in German and it's called Klampfomat:

http://roehrenfibel.files.wordpress.com ... fomat2.pdf



Schem of the Klampfomat as Harpomat with input-sensitivity-pot for different microphones, line-out and dummyload:

http://www.tube-town.de/ttforum/index.p ... 2672;image


This Harpomat poweramp topology is not class A, but hot AB. It's explained in the pdf why.
In short:
- it produces more even distortion, because one half of the sinus is always bigger than the other
- the transition from clean to crunch is very smooth
- it produces very much intermodulation distortion (that's what harpies want most)

[tubeswell]

What Martin said. Its kind of like a LTP. The cathode signal swing (the RK is unbypassed, and so functions sort of like a LTP tail) drives the tube that's on the side with the grounded grid. This is a non-inverting stage (whereas the other (input) stage is an inverting stage), so each side of the OT is being driven by opposing phases.