Before you swap power tubes on the Jolida you ought to set bias to the LOWEST and turn up accordingly.
I agree 100% but would add when I swap tubes I turn the bias to minimum - volume down to minimum and let them warm up for about 20 min. At that point I start to bias them up BUT not all the way. That's when I start playing music but not too loud for about another 10 - 20 min and look to see if the bias changed. I have found as I turn the volume up the tube starts to really work and heat up which influences bias. After a minimum of an hour but 2 hrs is better is when I make the final adjustment. Also keep an eye on the bias for several days after that. What I have seen is the tubes could take several to completely settle down. I have also found new tubes typically take 200-300 hrs to sound what there are going to sound like from that point on.
That being said I have an Octave V70SE that uses the same tubes. I have found changing the input tube (12ax7) will make the biggest difference in sound. My favorite now is not a 12ax7 but the Rca 5751 which has a slightly lower gain but sounds so right. After all the input tube is the first stage in amplification. Garbage in garbage out.
The drivers (12at7) controls the output tubes. For the normal *transconductance tubes (pretty much any *current production tube) I really like the Brimar 6060 yellow T or Amperex bugle boy ecc81's. For high transconductance you really want the Gec A2900/CV6091. They have the highest gain in the 12at7 family which will completely support high transconductance tubes.
* normal transconductance have a gain around 7000 where high transconductance tubes are over 10,000. Examples of high transconductance tubes are Shuguang Psvane - Eat kt88 diamonds - Ei Kt90 - vintage Gec/Gold lion/Gold Monarch KT88's. Note the Eat KT88 retails for $1800USD/Quad where the Shuguang Psvane is under $500USD/Quad for grade 'A' matching.
Good Luck
