Paul McGowan (PS Audio) owns both IRS Vs and Betas. He is friends with Arnie Nudell and has done extensive updates to his Vs. He has not mentioned working on his Betas. From Paul's website here is an interview with Nudell where he mentions his own preference for tube amplification, at least up to a point.
https://www.youtube.com/watch?v=-6mvhO8fVPs
https://www.youtube.com/watch?v=-6mvhO8fVPs