Be careful with KT-120 tubes in ST120

I decided to give the Tung-sol KT 120's a try in my ST120. Well, that was mistakes 1 through 4. I turned all 4 bias pots counter-clockwise and installed the 120's and turned it on. I went to adjust the bias and the meter showed 550 v (not mV). Turning the bias pots did not do anything. I replaced the Sovtek SSR solid state rectifier, and re-installed my 6550 tubes. Now, the bias on all tubes are 10v, but I am still not able to adjust it. I should have just left well enough and not wasted $ on KT 120 tubes, plus the cost of amp repairs.
Just curious if anyone has any idea what went wrong....

I have been running kt-120 in my st-120 hi-gain amp for many years no problem.

As it turns out, I had a defective KT-120. I installed a new quad, and the amp sounds wonderful. I would like to add that the protection resistor for each tube, worked as it was designed. Only had to repalce that resistor, install new tubes, and everything is fine.