Different Tubes and general purpose?


I’m trying to get a better midrange push or clarity out of my Line Magnetic 501ia tube amp.   Can someone help me understand what the specific function each type of tube performs in a power amp?  

I would like to upgrade several or all of my “stock” tubes but would like to understand where to start to beat enhance each aspect of the sound spectrum.   On my 501ia i have 4x KT120 and i believe those are power tubes, but please help clarify if wrong.  There are 2x 6SN7EH 1x 12AU7 and 2x 12AX7 (but the AU7 and AX7 look interchangeable to me).   As i look to upgrade where to i look to start, and why?  
Thanks in advance for help. 
gunners01

Showing 1 response by grey9hound

 I disagree , Differences in tubes can be very noticeable.
A perfect example is a Telefunken 12AX7 vs Mullard 12AX7 is Very noticeable. I have tried many 6SN7 and found very few to have any decent bass. That was verified by Andy of Vintage Tube Services.
The only Vintage 6SN7  with good Bass is the Ken Rads ,but 90 %  are Microphonic, or another with Bass is Tung Sol Black Plates(not sure of the year). The Sylvania 6SN7 has great Mids and highs, but is lacking in Bass. i have not tried New Production 6SN7s
Call Andy  616-454-3467
. tell him your amp . He can help, i promise. Maybe tell him which tubes in  which spots V1.V2, V3 ..etc.
Let us know how it turns out