Upgrading tube for a MAC 275 mk5 what are you using?

You just saved a bunch having the Amperex on hand.

The RCA 12at7's @ The Tube Store look good.

The tubes I did not recommend  are good tubes, just not for the type of sound you mentioned.

I have really fat sounding Ken-Rad dual flat plate 2A3's that I use Eastern Euro 12at7's with (balances out the sound), but stick with RCA/Mullard when running lighter sounding RCA and Visseaux 2A3's.

Most of my Amperex 12ax7's went into a friends Marantz 7 (wish I had more).

DeKay

DeKay,

Interesting about the Ken-rads I also have a set of triode labs 2A3 mono blocks I really like a set of NOS RCA grey plates I found. They are one of my fav NOS tubes right now for 2a3, supposedly the black plates are even better but I've not heard them. The greys are rather balanced sounding with very good bass control and detail. not rolled off on top and of course supper midrange. much better than any new production tubes I've tried. 

I find the RCA dual GP a "tiny bit" warmer in the midrange than the BP (my system), but like both equally.

I did prefer one slightly over the other when I tried Fostex bullet tweeters with my Stephens-Trusonic 8" single drivers, but forget which.

The 12at7’s I use to drive the Ken-Rad 2A3’s are RFT (Germany).

They make the RCA’s sound thin, but compliment the Ken-Rads.

An odd thing about the Ken-Rads is that they test in the low 80’s (same on two TV-7D/U testers) and I’ve never had an RCA surpass 66 (usually low-mid 60’s) for NIB).

I’ve spent 3 of the Visseaux 2A3’s (out of 6) and benched the last pair, plus a spare, for if I ever get a soft start circuit/rectifer amp.

DeKay