cathodyne phase inverter

[C Moore]

I was reading the Vox Night Train thread and it made me wonder.... I see the PI sends signal to the out tubes via the plates only. What is the advantage to this over a more traditional plate & cathode inverter?
Thank You

[Merlinb]

. What is the advantage to this over a more traditional plate & cathode inverter?

In short the advantages are:
A little bit more output swing is available, it is easier to overdrive the PI, the PI is less likely to produce nasty sounds when being overdriven, lower heater-to-cathode voltage differential, different tone (more 3rd harmonic).

[Bob-I]

I was reading the Vox Night Train thread and it made me wonder.... I see the PI sends signal to the out tubes via the plates only. What is the advantage to this over a more traditional plate & cathode inverter?
Thank You

Are we looking at the same schematic? It looks like a traditional cathodyne to me. What am I missing?

[C Moore]

I was reading the Vox Night Train thread and it made me wonder.... I see the PI sends signal to the out tubes via the plates only. What is the advantage to this over a more traditional plate & cathode inverter?
Thank You

Are we looking at the same schematic? It looks like a traditional cathodyne to me. What am I missing?

Yes, it is a cathodyne inverter. That is what my question was. Maybe I do not understand what you are asking?
I am looking at this schematic.....

https://tubeamparchive.com/files/vox_ni ... _h_121.pdf

[David Root]

hired hand I think you are comparing the cathodyne, which that definitely is, with the earlier paraphase type, is that right?

[C Moore]

What all of you guys are missing is...... the fact that I am an IDIOT. This stuff is all pretty new to me, and I am getting terminology and different PI circuitry all mixed up in my head. Cathodyne, Para phase, and what ever you call the situation like in a old Champ or Deluxe, where you only have 1/2 of a triode to split phase; so both the plate and cathode are used.
My apologies. Just suffering embarrassment from what is otherwise called "The Learning Process". Whatever question I really had in my head has been answered. Sorry for all the head ache, frustration and wasted time.
Thank You

[Phil_S]

The cathodyne (a/k/a concertina, split load) has no gain at all. It simply splits the signal for a push-pull type amp. The paraphase (less common) and long tail pair (more typical) provide some gain to the signal and will drive your power tubes harder.

Each has it's use. They are all good. "It depends..."

[sliberty]

As I think you realized, your premise was off. The Night Train schematic you linked us to (via the thread) actually shows the power tubes being fed by BOTH the plate and the cathode of the previous tube (the PI). One of the main reasons that this type of PI is used in a lot of designs is cost - only one triode is used instead of two like in a long tail pair. As Phil pointed out, it has low gain (not quite unity), and over time this sort of PI fell out of favor except in those cases where using one triode was key. I suppos that since the preamp used three triodes already, a single triode PI was a design decision at Vox to keep the tube count from growing.

[Phil_S]

... since the preamp used three triodes already, a single triode PI was a design decision at Vox to keep the tube count from growing.

I'd agree this is one likely explanation. Another is that the three triodes already developed enough gain that more gain at the PI may not have been desirable.

[C Moore]

As I think you realized, your premise was off.

Yes, I dropped about every ball there was on this one. Oft' times, my desire to learn operates at a much faster pace than my capability to do so. Once again..... You guys have been real square with me. I appreciate it.
Thanks