I don't recall if it was the removal of the auto-bias, replacement with a different circuit, or something else, but there was something in the electronics on the original that made them burn out with some regularity. I had a YBA-200 that this happened to. I sent it back to Traynor and they upgraded it to YBA 200-2 specs which I gather was their policy.
It didn't happen again, but I later sold it and got a Peavey VB2 which doesn't have quite the same pillowy roundness (though it's close) of the YBA200, but is a heck of alot louder.
If you are considering a first gen YBA-200 check with Traynor to see if that particular serial # has been fixed before, and if it isn't, is it still under warranty to be fixed if it blows.
Also, it's an amp that breaks up rather quickly. Unless you're really into grind and distortion I highly recommend the "low-gain" retube kit from eurotubes https://www.eurotubes.com/cart/index...category_id=88
or at least switching out the 12ax7's with ECC81's ( 12AT7's ).
I did this and it cleaned things up nicely and gave me alot more headroom to play with.