2 Channel Recto FX Loop issues

[jdgebha]

I thought I had found my issues earlier with the Send Pot being bad but alas I am stiill having issues. Running the FX Loop for a MXR EQ, Boss Delay and a MXR Chorus. Everything seems fine but then a few minutes into playing the sounds just cuts out on both channels. If I bypass the loop both channels are fine. I can't put my finger on it. Anyone ever hear of this?

 

[cardinal]

Bad tube for the FX loop?

 

[jdgebha]

All tubes in the pre amp have been swapped. It happens after maybe 6 or 7 minutes of operation.