Blackvibe 6L6 Strange behavior on tone pots

[retodellatorre]

Hi everyone

So i changed the middle pot to a A 10K and removed the 6.8k to ground (just ground). Still the EQ Settings with treble middle bass, seemed not to match. I could turn the knobs as much as i wanted - i did not feel AB763 like.
My critical test is using only a XOTIC RC booster in front of the amp. With the changes above the rc sounded harsh and fuzzy - in no way i had it like in front of my super, with that nice tiny chrunch sound.

So i figured since the original Vibroverb also had no middle i have to check further how a blackface with Middle Pot is build. The one difference is, that there is a 0.022uf cap at the tonestack. So i replaced the 0.047uf with a 0.022uf - and there we go.
No it feels like a Blackface with middle and i can now mix treble middle and bass in a way i expect it from a blackface. Also my RC test is now just as it is on any blackface not only AB763.

Based on my research i think almost all blackface without a 10K Middle hat a 0.047uf at tonestack (Princeton, Delxue, Vibroverb) but the once with a middle (Super) had a 0.022uf.

Greetings Reto

[Stevem]

If your looking for any mid boost with aFender type tonestack the only way to get any of that or even get a flat response out of it is to turn the volume way up, crank full up the middle and set the bass and treble very low.

[martin manning]

So i changed the middle pot to a A 10K and removed the 6.8k to ground (just ground)... ... So i replaced the 0.047uf with a 0.022uf - and there we go.

Thanks for the update. Makes sense.