unbypassed cathode resistor and ultra-linear operation?

[CopperWings]

Hello you guys! I'm really excited to be a part of ,probably, the best forum on the net.
So here it goes... I've looked for info and examples concerning unbypassed cathode resistors for power tubes in ultra-linear but haven't really found anything so I was wondering if any of you guys could point out any adverse effects this configuration might have, any obvious shortcomings or anything I should keep in mind. I do know about cathode degenerative feedback and the, crudely put, feedback introduced by the screen grid in ultra-linear mode. Just to clarify this is for the 6L6 family of tubes run single-ended...

[pdf64]

I think you may be treading uncharted territory with SE unbypassed cathode.
I can't see that leaving the cathode unbypassed would have much in the way of benefits, and would likely increase output impedance, thereby counteracting an advantage of UL operation.
What benefit do you perceive it may bring?
Pete.

[Jazz P Bass]

A bypassed cathode will certainly have a fuller frequency response.
Adding a negative feedback loop off of the output will also see an increase.
Here is a link to a fellow that makes SE hifi amps.
In it there is a discussion of bypassed & unbypassed.
Link: Single Ended Tube Amp project

[Merlinb]

Hello you guys! I'm really excited to be a part of ,probably, the best forum on the net.
So here it goes... I've looked for info and examples concerning unbypassed cathode resistors for power tubes in ultra-linear

Just start with a conventional bypassed UL design, then simply remove the bypass cap!
The result will be lower gain in the PA, wider, flatter frequency response, poorer PSRR, more headroom. I've never tried it myself, but it won't hurt just to remove the cap and see how you like it.

[pdf64]

The result will be lower gain in the PA, wider, flatter frequency response, poorer PSRR, more headroom

I can't see how the PSRR (power supply rejection ratio?) or headroom (as in system gain before clipping) would be affected?
I'd be grateful if someone could assist - Pete.

[tmod]

I can't see how the PSRR (power supply rejection ratio?) or headroom (as in system gain before clipping) would be affected?
I'd be grateful if someone could assist - Pete.

An unbypassed cathode resistor will result in local feedback, increasing headroom.

Unless I'm wrong, the reason PSRR goes down is because any ripple current through the valve will result in a signal appearing across the cathode resistor. This will appear as a grid-cathode signal, and will thus be amplified by the valve. With a cathode bypass cap any rippple current will be shunted to ground, and there will be no noise signal appearing at the cathode.

[kg]

no reason the two can't happy co-exist in an output stage.

i myself love UL zero loop nfb finals.