Can't adjust tube Preamp balance control

Looking for some advice. I have a Spectron Musician II with Hybrid upgrade and Audio Valve Eklipse with balance controls that was working perfectly. I then change the Spectron from single end to balance via the inside switch. I also replaced the stock tubes with RCA clear tops.

I turn everything back on and the balance control effectively doesn't work. When I turn the control all the way to the left or right it doesn't affect the sound as sound is now come out of both speaker regardless of where the balance control is set at.

Could it be the tubes or the Spectron operating in balanced mode? I would appreciate any response and suggestions.

Thanks.