Cold clipper causing unstability

[Colas LeGrippa]

On a 4  preamp stages amplifier ( my design ),
I had originally put a 33k cold clipper on the last stage  in order to maintain the gain to  a decent level and the police from my appartment building . But I had to swap it for a 10k to get stability I was looking for. Does somebody knows  the reason for that ?
The amp is a 50w , 2 × 6CA7, 3 × 12AX7,  plate driven,  k bias with.bypass cap, each tube biased at 16.5 W aprox. Thanx.


Colas

[thetragichero]

posting a schematic would likely get you more helpful responses

[Latole]

What is a "cold clipper " ?

Cola La grippa, you will always amaze me with your knowledge.

Google;

Cold Clipper Gain Stage

The cold clipper gain stage is a very useful tool for voicing an amp's overdrive tone. It is used in many high gain tube amps to generate early and smooth sounding overdrive tone.

For minimum distortion a tube should be biased halfway between cutoff (when all electron flow is stopped) and saturation (when electron flow is maxed out). A 1.5k cathode resistor for a typical tube amp 12AX7 triode gain stage is very close to center bias. A cold clipper's very large 10k to 39k cathode resistor sets a cold bias that leaves very little room on the cutoff side so the guitar signal can easily be clipped when the signal's negative lobe on the grid reduces electron flow through the tube and electron flow is shutdown completely. The cold clipper is designed to clip on the cold side of the operating point. This clipping is asymmetric because there's plenty of room on the saturation side of the bias point so the guitar signal's negative lobe is clipped while the positive lobe passes unmolested and carries the original musical content. Asymmetric clipping generates ear pleasing even order harmonics and minimizes nasty sounding odd harmonics. When a guitarist pushes a tube amp hard enough to get symmetric clipping, using volume control or pick intensity, odd order harmonics greatly increase making the overdrive tone sound more "angry", giving fingertip control of the guitar's "mood".

More here, scroll down to middle

https://robrobinette.com/Tube_Guitar_Amp_Overdrive.htm

[Colas LeGrippa]

Thanx Latole for posting that nice info on cold clippers. Now Thetragichero and PDF64 know what it's all about

[pdf64]

…
I had originally put a 33k cold clipper on the last stage  in order to maintain the gain to  a decent level and the police from my appartment building . But I had to swap it for a 10k to get stability I was looking for. …

That seems kinda topsy turvey, opposite to what might normally be expected.
As more gain generally equates to a lower margin of stability, all else being equal.
More info needed before it’s feasible to hypothesise why it might be behaving like that.

[Colas LeGrippa]

Very  strange indeed