ampeg svt mti

I'm back again, just put valve art 6550a's in my newest acquisition and I'm biasing according to procedure listed on the amp. I bias one side to 72 millivolts (reads 72.4) and between k1 and k2 to precisely 0 mv(and it's exact too). My question is the balance control. If I run it down to zero...

Not really sure why I've done this but I bought a Mti svt that was on Facebook marketplace and traded a little unused gear for it so I'm not in it too deep. I got it relatively cheap as it had a redplating tube. I got lucky, and as it turns out the problem follows the tube. With a spare in it it...