Fender Quad reverb. Reverb issue.

[Damia]

Hi everyone.
I've got a Fender quad reverb, which is basically a twin reverb with four spekers.
It works good but when you turn it on, reverb works for about 5/10 minutes and then doesn't work anymore.
Any suggestions?
Thank in advance!

[The Dude]

Welcome to the place!

I would first try subbing V3 and V4 with known good tubes (you can try them one at a time to see which might be bad). You could have a tube dying after warmup.

[Enzo]

Or considering its age, some of the capacitors in the trem circuit are dried out.