[Yaesu] re 572B's in FL-2100

[Fern Rivard]

    Could some please enlighten me as to the best tubes to use as
replacements in Yaesu FL-2100B amplifier.  I see that RF Parts carries at
least three different brands. It looks like the Taylor replacements are the
best buy but there is a warning that using the Svetlana brand would require
a modification to the FL-2100 amp. What is this mod that they are talking
about?
    Another supplier only carries the National brand which I have never
heard of before but they are made in China. My guess is that those tubes
can't be used in the horizontal position.
    Any comments or suggestions would be greatfully appreciated.  73's from
Fern