Difference between 6DQ6A and 6DQ6B?

[K5DH]

What's the difference between a 6DQ6A and a 6DQ6B?
My tube manual is an older book that lists only the
"A" version. Can I use a "B" version in a DX-20
without changing any of the rig's component values?

73,
Dean K5DH