Just picked up a MusicMan HD 130 Bass head Tube Biasing Questions

Nighttrain1127 · June 04, 2014, 06:58:33 AM

Hi I just picked up a MusicMan HD 130 Bass Head. The previous owner had installes New EL34B tubes in it (About two weeks ago) but has not had it Bisaed. I Have Biased My Ampeg SVT's before with no Issues. Just wondering what the procedure on this amp is and what voltages am I looking for. . Also if anyone knows where I can find a copy of the manual that information would also be appreciated.

drbassman · June 04, 2014, 08:15:37 AM

I had two, sold one and still have the other. I couldn't find much on them. I take mine to a local amp tech who specializes in tube amps. Sorry I can't help.

Nighttrain1127 · June 04, 2014, 08:40:46 AM

The Nearest Amp tech that works on tube amps is over 50 miles away. Just thinking some one must have some info or can lead me in the right direction. This should be a simple thing but information on these is Hard to find as you posted. Just would like to avoid having to pay for something I can do myself. But thanks foy your input. At least I know I am not the only one having trouble finding info on these.

Pilgrim · June 04, 2014, 09:53:32 AM

PBG will be along with more info. I'm not sure that all amps are even designed to be biased, but my bet is that he will know.

Granny Gremlin · June 04, 2014, 10:31:56 AM

Yeah, just wait for Psycho.

You can bias any amp, the issue is that not all amps have a bias pot; the rest of the time you do it by changing resistors.

Psycho Bass Guy · June 04, 2014, 11:23:02 AM

If the amp is working and has no sonic issues, leave it alone. HD130's run in Class AB2, favoring the "B" part of that mixture and use VERY high voltages (SVT-level) to operate. Get it wrong and you'll lose a set of tubes, speakers, and major amp components in short order. In the SVT, AB1 doesn't really apply until the driver tubes' grids are pushed positive, not so with the HD130, which Leo made as an even cleaner version of the already clean Fender Twin. If the outputs are biased any hotter (towards class A) than the tubes can take, it gets very bad in a hurry.

Nighttrain1127 · June 04, 2014, 03:06:36 PM

Thanks to all who posted this is indeed a very friendly and helpful place. Thanks Psycho Bass Guy for the information. If i start having sonic issues I guess it will then be tech time.