I've found from extensive static and dynamic testing, that the 6AV5GAs behave more like "mini" 300Bs, than 6B4Gs. A few test runs on Tube CAD,
inserting my voltages, currents and OPT data, confirms this - the 6AV5s track within 2% of 300B, and about 10% of 6B4G.
Just run them with around 280-300V K-P, and 66 to 68 mA IK, and the PD between 18 and 20 Watts, and then they will "strut their stuff", and sound their best.
I prefer the Sylvania and Dumont "large plate" versions. Ditto for 12AV5GAs.
I use SRP drives, but I'm sure that the G*S*G and Clementine boards will also play very well with the 6/12 AV5GAs.
Back to the original question - the Transcendar OPTs are excellent!
/ed B