Your problem is your budget will put you in the older units near rebuild time Capacitors especially older units caps start drying out in 10 years loss if fidelity
like hearing less and less , resistors too far better out there now ,old carbon type warm but gritty vs the new 1% Takman orDale Vishay for example
coupling caps , put in VH audio Odam small but very good find a good tech
and high offender the crappy old tube sockets , for $25 each you can get far better Teflon gold over Copper ,I experimented just changing the tube sockets a solid 10% increase in fidelity why 3x or better conductivity ,and far less resistance pit was like installing a good vintage tube ,I was shocked this was 7-8 years ago.
everything counts put it on credit buy new , the LTA micro Zoe would be perfect.
another overlooked element the volume pot itself you loose a lot of micro detail and imaging using a $25 Alps or Bourne volume pots ,they are just conductive plastic wipers , many older and new preamps use them why $$ to save
you should just go to Schiit audio and buy the Freya + put a decent aftermarket power cord like the Pangea sig mk2 -$200
and buy good NOS tubes 6SN7. I have this in my backup system with nice tubes
go to Brent Jesse recordings, or vintage tube services , I don’t know your cables or front end ,each tube sounds different , check it out ,it is very respectable with good new old stock tubes I put 1958 Raytheon tubes in there very nicely balanced
the best are probably the 1940-50s Tungsol top oval getter, or sylvania silver metal collar base tube , but $$ , hint hint Many companies has their name put on the tube like Hammond organ , Delco ,Fisher ,when in fact rca, or Sylvania and brand new and tested you can even buy a 2 year warranty for $15 a tube , these off names tubes are less then 40% of the correct name brand , . Brent Jesse Carrie’s a lot of these .having been into modding Everything over 20 years , and tubes over 40 years and owned a Audio store and had service techs learned a lot .
just check out the Schiit audio brand $895 and just buy your own tubes.
NOS far better then these Russian fake Tungsol they are using the quality ,sonics,and longevity , not in the same league.