Ampeg B15s oscillation problem

[stagam]

I have Ampeg B15s amp that I recapped and can get great signal up to output tubes 7027 but has oscillation at full volume with nothing on input. Anyone out there that can assist me with problem?

[tubeswell]

NFB loop backwards?

[cfortner]

NFB loop backwards?

Gridstopper at V1? Resistor to ground at grid of V1?

[pdf64]

I have Ampeg B15s amp that I recapped and can get great signal up to output tubes 7027 but has oscillation at full volume with nothing on input. Anyone out there that can assist me with problem?

Are the shorting contacts on the input socket functioning correctly, ie shorting the input stage grid to ground when nothing is plugged in?
Is this the correct schematic for the amp in question? https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_b15s_revd.pdf