Studio 20: power tubes.

[classicampguy]

i'm making plans for upgrades to my studio 20. After I build m own sealed 112 ext. cab with a vintage 30, I plan to replace the rocket 50 in the combo with a greenback. The other half of it comes from testing different tubes until I find the ones that suit me most. I logged on to the forum a while back to see If anyone had changed the tubes in their studio20 and which one's the would recommend. i noticed on one post that one guy didn't want to change the TAD's out because he would have to re-bias. Biasing isn't a problem for me, I an do it, So I didn't think on it. But I recalled that while looking under the hood,so to speak, I never saw a biasing knob. I know I've seen the biasing knob on the bottom of the chassis in plain sight on the stage 60, so I did the logical thing and looked in the manual. On the first page (really the 7th page, but the first to refer to the amp and not health hazards,) It plainly states, "The carefully voiced preamp and cathode biased dual EL34 power amp configuration provides the user with the ability to create wonderfully lush valve tones." Cathode biasing, there's the culprit. If I'm correct, cathode biasing is a common form of "self-biasing" used in the preamps of many tube guitar amps. It is done by applying a constant positive voltage to the cathode, naturally making it x-volts more positive than the input signal. This eliminates the need to forward bias at all. I don't think that the people at the blackstar headquarters would lie to us about that, so feel free to change out your power tubes. Just insure that they are indeed El34 (or 6CA7) types.

[auburnshredder]

Lot's of threads on this subject...yes from what I have gathered the HT-20 is self-biasing. I changed out all four of my tubes with JJs three months ago and have had no problems at all. Good luck wiht the cab...I have not tried a V30 yet in my HTV112 cab. I have used the stock Celestion 70/80, a G12H anniversary and my current speaker, an Eminence Private Jack. I ike the Eminence the best so far.