With power tubes what may sound good in one amp is no guarantee it will sound good in a different amp circuit .
i have been through this for over 40 years . Never Assume.
regarding kt150 tubes a very good tube but,if the transformers are
not optimized for them you are removing the design overhead
and under duress msy create distortions, check with the mfg first.
Small tubes for balance pre 1955 Amperex slanted D getter long plates are excellent, Mullard 10 series for a warmer midrange
and Siemen, or a Tele I am referring to a pair in the $300 range
there are rare models that are $$ but almost impossible to find .many American tubes were also very good back in the 50s,and before late 60s
i have been through this for over 40 years . Never Assume.
regarding kt150 tubes a very good tube but,if the transformers are
not optimized for them you are removing the design overhead
and under duress msy create distortions, check with the mfg first.
Small tubes for balance pre 1955 Amperex slanted D getter long plates are excellent, Mullard 10 series for a warmer midrange
and Siemen, or a Tele I am referring to a pair in the $300 range
there are rare models that are $$ but almost impossible to find .many American tubes were also very good back in the 50s,and before late 60s