Gold Lion KT88's Upgrade

I recently retubed my MC75 mono amps and used a matched quad of the Gold Lion's with great results. I can recommend them. 

RAM Tube Works offers Gold Lion KT88's in sets matched as close as humanly possible, and comprised of the best examples of the tube.

you should consider the Shuguang Western Electric red base KT88s.

best KT88 I have heard, including many NOS varieties. Shuguang has done their homework on plate and cathode metallurgy.

they are not cheap, but are open and airy, give a great sound stage and are super at dynamics.
 

You cannot go wrong with New Sensor's reissued of the Genalex Gold Lion KT88 tubes  They are well made, good sounding, reliable and well priced tubes. 

I have not kept up with all the Shuguang / Psvane KT88 variants, but I am always wary of companies that produce new versions over a relatively short periods of time.