Using 12AU7 instead of 12AX7 to lower the gain

[Helmholtz]

Of course I can't exclude a microphonic PU, but I thought EMGs were fully potted?
Maybe try a different guitar.

Controlled string feedback can be great, but I spoke of uncontrolled FB.

If the PU itself vibrates relative to the strings, all kinds of squeals are possible.

In any case, either sound level or gain (more exactly compression ratio) needs to be reduced.

And of course better not stand in front of the speaker.

[Chuck H]

If the PU itself vibrates relative to the strings, all kinds of squeals are possible.

Ah, yes. Another possibility. I actually had that problem once. I ended up replacing the pickup springs with sections of rubber tubing as well as using stiff foam in the pickup cavity to wedge the pickup in place a bit. I'd forgotten this until now.

[kg]

With the drums, bass, other guitar player, singer... no I can not turn the volume of the CH3 down. I need minimum at 10 o'clock. That means that Gain pot can not go over 9 o'clock without getting feedback. With Gain pot set so low, I do have enough gain, but the sound is flabby, loose, it's not tight. Read that some people used 12AU7 and that gave them use of full range of the Gain pot. I am just worrying about possible damage to the amp or tube..

having recently picked up a 5150 III 100S ("stealth" modded), i might be able to chime in here.

indeed this amp has a superfluous amount of gain, especially on the red channel.

swapping in a lower mu triode in v3 will affect the red channel only. it will allow you to turn the "gain" knob up, and achieve the same basic result. however, i can tell you that from decades of playing high SPL situations, as the volume goes up, the gain MUST go down. consider the system as a whole, strings, pickup, preamp, poweramp, speakers. there is NO WAY to have any sort of control with the red channel maxed out on gain and any kind of wattage coming from the speakers. it's designed to give you a saturated tone at bedroom levels.

also there are techniques that mitigate high gain situations such as distancing yourself from the cabinet, being diligent about switching to a low gain channel when pausing playing, etc.

before swapping tubes i would lower the gain knob to about 12:00 and try to get your tone back by twisting the other knobs... ie, you can bring back some "distortion" by boosting high frequencies.

on my 100w version i get separate gain/tone stack/post controls for each channel. i read on facebook that there is a retrofit kit to provide the same function to the 50w versions by replacing daughter boards and pots. the blue crunch channel is preferred when the volume in the room gets up there, for the very reasons you've discovered.

ken

[Emetal]

having recently picked up a 5150 III 100S ("stealth" modded), i might be able to chime in here.

indeed this amp has a superfluous amount of gain, especially on the red channel.

swapping in a lower mu triode in v3 will affect the red channel only. it will allow you to turn the "gain" knob up, and achieve the same basic result. however, i can tell you that from decades of playing high SPL situations, as the volume goes up, the gain MUST go down. consider the system as a whole, strings, pickup, preamp, poweramp, speakers. there is NO WAY to have any sort of control with the red channel maxed out on gain and any kind of wattage coming from the speakers. it's designed to give you a saturated tone at bedroom levels.

also there are techniques that mitigate high gain situations such as distancing yourself from the cabinet, being diligent about switching to a low gain channel when pausing playing, etc.

before swapping tubes i would lower the gain knob to about 12:00 and try to get your tone back by twisting the other knobs... ie, you can bring back some "distortion" by boosting high frequencies.

on my 100w version i get separate gain/tone stack/post controls for each channel. i read on facebook that there is a retrofit kit to provide the same function to the 50w versions by replacing daughter boards and pots. the blue crunch channel is preferred when the volume in the room gets up there, for the very reasons you've discovered.

ken

Thank you for such a in depth analysis, I know and I agree with you on all points. The only thing you probably did not see is - my gain on red CH is on 9:00 so I can not "lower the gain knob to 12:00" But everything else I agree. Anyway, I'll just keep using lower mu triode at V3 or V2 position, wherever I like it the most and that's it. CH 2, the blue one, is what I use anyway. I was just looking for options to maybe sometimes use CH3, if ever.