Vox Cambridge Reverb 1967

[fgcarter]

I've kept my Vox Cambridge Reverb for all these years. Great little amp which I used as a power head for a Leslie speaker cabinet and Vox Continental Organ. Now that I no longer use the Leslie, I've reconnected the Celestion Bulldog 10" speaker that is original with the amp. I get feedback seemingly from the reverb, but even when I turn off the reverb and turn the sound down to "0", the feedback persists. Can yo suggest a way to eliminate this feedback? It never happened even before I connected the Leslie speaker and does not feedback when the Leslie is connected. Help!

[Mincer]

Welcome to the forum!
Is this a tube amp? A microphonic preamp tube can cause this type of feedback. If you can, try to make either a sound clip or video.