5E3 with different PI

[Leevi]

Does anyone have experience in using different kind of PI like AB763 PI
together with cathode biased 5E3 power tubes?


Would it work?


/Leevi

[DummyLoad]

yes. graft in BF deluxe PI. discard NFB loop & insertion 47R. overall gain will be less with LTPI though.


--pete

[VMS]

Maybe something like 5g9 tremolux without the trem and cathode biased.

http://ampwares.com/schematics/tremolux_5g9.pdf

[robrob]

Yes it will work. A blackface long tail pair phase inverter is a gain stage (the tweed Deluxe's cathodyne phase inverter isn't) so the amp will drive the power tubes harder which is a good thing.

The LTP PI also has a sweeter distortion tone than a cathodyne PI too so it should have a tighter, more modern distortion tone, especially when pushed with pedals near max volume.

[Fresh_Start]

Yes it will work. A blackface long tail pair phase inverter is a gain stage (the tweed Deluxe's cathodyne phase inverter isn't) so the amp will drive the power tubes harder which is a good thing.

The LTP PI also has a sweeter distortion tone than a cathodyne PI too so it should have a tighter, more modern distortion tone, especially when pushed with pedals near max volume.

I could be wrong but think that a gain stage plus cathodyne like the 5E3 has significantly more gain than a long-tailed pair. OTOH cathodyne has unusual distortion when pushed too hard.

Chip

[robrob]

You are correct Chip and the second half of your post explains why the long tail pair phase inverter is so ubiquitous in post tweed era guitar amps.

[PRR]

> gain stage plus cathodyne like the 5E3 has significantly more gain than a long-tailed pair.

2X or 3X.

Separate gain-stage can develop full gain; long-tail gives half-gain to each side.

Further the separate gain-stage only has to drive the near-infinite load of cathodyne grid, and can be optimized for more gain (less load-pulling grunt). The long-tail typically has to face the power tube grids directly. If these are fix-bias then they should be around 100K, quite low for a gain-stage. (But we often cheat-up to 220K.)