Here is my latest tube rolling experience with the Transporter: Type 83 for rectification and 6H8C for output. These tubes are relatively cheap compared with other well known types.
What I found out was that at least for the type 83 tubes, that the sound is different with a different combined plate current value on the output tubes. And I can hear a difference of sound with a change of .01mA of the combined plate currents of the output tubes. Example of tube configurations:
(out1 p1) (out1 p2)
x.xxmA 7.00mA (combined = 14.68mA)
(Type 83 tube1)
(out2 p1) (out2 p2)
7.68mA x.xxmA
-------------------------------------------------------------------------------------
(out1 p1) (out1 p2)
x.xxmA 7.35mA (combined = 14.69mA)
(Type 83 tube1)
(out2 p1) (out2 p2)
7.34mA x.xxmA
x.xxmA are plates not being used by the Transporter. If you switch the output tube's positions then those plates will be used instead. In almost all cases, the combined values will be different between the two sets. I don't know if the plate currents of all the plates are the same in the grade-A Black Treasure tube pair, or they are just very close between them.
A higher combined plate current value will have a more compressed sound. A lot lower value will produce a some what a flabby sound. One need to find a value that produces the sound you like, such that you will hear the sound of the string vibration of an instrument rather than more of a woody sound of the strike on the string.
I found GE, RCA, Sylvania brands of type 83 sounded similar, but they each take on a different ranges of combined plate current values of the output tubes. The key is to find a good match of combined plate current of the output tubes to sound the best/right. IT WOULD BE NICE IF THERE IS KNOB RIGHT AFTER THE OUTPUT TUBE TUBE-CIRCUIT ON THE TRANSPORTER SO THAT ONE CAN INCREASE/DECREASE THE CURRENT VALUE. Given two tubes of the same brand of type 83 tubes, each may need to use a different set of output tubes with different combined plate current values to sound the best.
Type 83 tubes have mercury vapor in side the glass, similar to fluorescence light bulbs & compact fluorescence light bulbs (the government is forcing everyone to use in the near future). Mercury vapor will escape into the air if the glass is broken. Mercury vapor is toxic.