[Capt Rosebuddy]

So, I burnt out one of the power tubes on my Blues Jr amp. It came loaded with Groove Tube EL84 tubes, its my understanding that another brand of tube will work ie Mesa. Further, I gather that the power tubes need to be changed as a "matched set" and then the amp needs to be re-biased. My question(s) are: Will any brand of EL84 tubes work and what are the characteristics of another brand and..Is re-biasing something that I can do myself with my limited knowledge of amps and electronics? Also there is a special tool that you need to use?? Has anyone performed this operation on a Blues Jr at home and lived to tell about it? Sorry its not really a GD gear related problem, but I trust the advice here over just about any other source.

Thanks

[myoung6923]

You are right that they need to be changed out as a matched set.

Different brands of tubes have different sonic characteristics. Even different batches of the same brand sound slightly different. Then, also, new tubes break in after a burn in period. Some places - like Lord Valve - sell them already burned in. Unfortunately there's not a whole lot that you can do to test them out before you buy them. A lot of places will let you send them back if you don't like the sound.

I've had good luck with Tung-sol and TAD small bottles - but others are good as well - JJ, groove tubes, I've heard good things about EH tubes...

While you should rebias after changing out the tubes - if the new tubes are close to the same value as the old ones then you can get away without having to do it at all. No - it's not something that you should try if you aren't pretty good with amps and electronics. If you are, then you'll need to get a kit that will plug into your tube sockets and then the tubes plug into it - you can then measure the voltage to each tube and adjust accordingly. My feeling is - try out the new tubes - if it sounds too weak or if it's breaking up too early then bring it in for rebiasing - it shouldn't cost too much.

[RiverRat]

Groove Tubes are rebranded SovTeks...

I believe the Blues Jr is cathode biased... so there should be nothing for you to do except replace the tubes with a good pair of EL84's...

[Capt Rosebuddy]

Done! thanks for the input guys, I got pretty much exact replacements, and they sound fine, actually better than ever. So I think I'll skip the biasing step.

[strumminsix]

You are right that they need to be changed out as a matched set.

Keep in mind that the statement is best practice.

From guys I know who were playing back in the 60s it was common to simply take out the burnt tube goto the closest spot that sold tubes (even 7-11s sometimes) and pop the new one in without bias or matching, etc.

I do replace all mine in sets when upgrading worn tubes but never fear having mismatched.