Self-Split Phase Inverter

[tschwarz]

Hi all,

I came accross a rarely used PI variant I'd naively call "self-split", just like those archaic self-split power stages but with triodes set up as a phase inverter followed by a pair of power pentodes (EL84). Basically an LTPI without the long tail. Marshall used this design in the 2022 from the late sixties, Komet copied it almost verbatim into their 19 and 29 models.
Does anybody know the "official" name for this style of PI? Anybody here have any hands-on experience with something like this in a build? I'd really like to try one on my next build (a TW-ish pre-amp into a quad of 6BW6s) ...

Cheers, Tom

[martin manning]

Looks like a version of a long tailed pair to me, Hiwatt used something similar IIRC.

[Lynxtrap]

Looks like a DC coupled LTP. http://www.valvewizard.co.uk/dcltp.html

[tschwarz]

Looks like a DC coupled LTP. http://www.valvewizard.co.uk/dcltp.html

OK - thanks! That's it - exactly...

Cheers, Tom

[WiderGates]

Looks like a DC coupled LTP.

Hello, if you look at the whole schem you can see that it is NOT DC-coupled.

[jabguit]

https://www.valvewizard.co.uk/dcltp.html

[Lynxtrap]

Hello, if you look at the whole schem you can see that it is NOT DC-coupled.

The PI is DC coupled via the cathode. The .1 cap on the grid of the 2nd triode is AC ground. Any signal coming into it from the preamp is of course AC coupled to the PI.

[martin manning]

Any signal coming into it from the preamp is of course AC coupled to the PI.

Is it? We can't see how the input is coupled to the previous stage, which is what the AC or DC coupled designation refers to.

[Lynxtrap]

Is it? We can't see how the input is coupled to the previous stage, which is what the AC or DC coupled designation refers to.

Sorry, by bad. I got confused about the DC aspect, just recognizing it as a school book example of a DC coupled LTP from the schematic posted and seeing the sine wave at the input on ValveWizard's drawing.

It's seems to be an AC coupled PI that looks like a DC coupled PI. I guess it's an AC coupled "short tailed" pair...

https://www.audioservicemanuals.com/m/m ... -schematic