LTP vs See Saw

[Smitty]

Hey guys. I haven't been here in a while. I see things are still going strong. Congrats to the regulars who've been helping out for so long. I admire you.

I've been running a typical Fender LTP in my amps since the beginning. The zener thing in the grid circuit helps a lot (Thx, Ray). I'm looking to get a little rounder clipping at the grids of the output tubes. I'm thinking about using a 12AU7 instead of a 12AT7 phase inverter. With the existing power supply ladder there just isn't enough B+3 to net very much plate voltage using an LTP. The current in the tail sucks it all up.

Has anyone tried the Ampeg VT40 PI?. It's a voltage gain stage in front of a see saw. What happens to the see saw when you hit zero volts on the output tubes? Do things go crazy or does it hang together? Would it compare favorably to an LTP? Any experiences? I suppose I should just try and see what it looks like on the scope.

The Valve Wizard explains see saws

Thanks,

Smitty

[pdf64]

I think fender used this with the 5D3, and Vox with the AC50.
When I've tried it, it's fine clean but can get some horrid distortion when overdriven. Due to coupling between the linked cathodes, I think.
I got rid of it by seperating the cathode resistors and bypassing them.
But I went back to cathodyne or LTP phase splitters as they overdrive nicely.
I think that you might be better to use cathode follower buffers after an LTP (which might supply grid current to the power tubes, = class AB2), but haven't tried that myself yet.
Peter.

[Don Moose]

Any particular reason not to adjust the values in the dropping string so you get a higher B+ on the PI plates? Shift the PI B+ tap point 470 to 620 ohms 'higher' in the string, say.

Hope this helps!

[Don Moose]

Any particular reason not to adjust the values in the dropping string so you get a higher B+ on the PI plates? Shift the PI B+ tap point 470 to 620 ohms 'higher' in the string, say. Maybe even 1k.

Hope this helps!