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Modifying a Buster 200

bassfuser

bassfuser

Jul 16, 2008
528
335
#1
I am thinking of putting a couple of holes in the bottom of the chassis to install speakon connectors. One for 4 ohms and one for 8 ohms. I'm also thinking of adding a multi-turn pot for a bias adjustment. I've seen where you can get chassis mounted pots but that would require another hole in the chassis.

I was just curious to what the consequences of such mods may be. I know a lot of people want the amps in original condition and putting holes in the chassis definitely prevent one from returning to original shape.

Would I be able to get what the amp is worth if I decide to mod? I really don't have plans to get rid of the Buster anytime soon, but I'm still hesitant to make these changes.
 
#4
I don't see a bias-adjustment mod hurting the resale value of the amplifier -- it's a functional mod that is almost a requirement on the Boogie tube amps. Just keep it up and out of the way -- I had this done to both my amps (Buster head and a Bass 400). 'Course, mine is just a simple bias pot.

The speakon connector, OTOH, seem like a stretch. There's really very little room for speakon connectors -- you'd have to mangle the aesthetics of the amp to accomplish this.
 
#5
Paul,

I used to be a tech in my former life so I know about working on tube circuits. Thanks for the concern though.

I probably don't need to have the pot mounted through the chassis, but I figured it would be nice to have access without pulling the amp out of the cabinet.

As far as the speakons, I haven't checked to see if there is enough room to go out the bottom. Another alternative I was thinking would be to replace the inner 1/4 outputs with the speakons. I'm really not sure if they would fit, but just an idea at this point.
 
#7
jetofuj said:
Do you really need bias adjustment? Boogie knowingly doesn't provide such option.

Just asking. I'm not an expert but I might become Buster owner in the next few days.
Click to expand...

This is a hot topic in the amps forum

Adding a bias adjustment is a popular mod. However, even though Mesa documentation claims you MUST use their branded tubes, you really don't need too (and arguably shouldn't). The amps are designed with a wide bias range - all you need to do is order tubes from a reputable seller and let them know what amp you're buying tubes for.

OK, let the tomatoes fly! :hiding:
 
#8
In many respects RCC is correct. Back in the day tubes were of a consistent quality and a manufacturer could specify a bias range that the tube supplier must select. No longer true as it once was. You do not need to use Mesa tubes but if you don't you have to have the bias set up for whatever tubes you install. Decent Techs check the bias as a matter of course every time they have an amp apart. If you want the most out of a particular set of tubes you must set the bias according to what the tubes tell you.

Paul
 
#13
jetofuj said:
Sorry, I'm confused. Does Buster have some sort of bias adjustment pots inside? No?
Click to expand...

They have a fixed resistor so you can't adjust the bias. That's why they insist that you buy their tubes. They have a good point that they designed the amps and know the "Sweet" spot, but I've read that they run pretty cold. I've also read that their tubes kind of suck. (Maybe other tube manufacturer propaganda.) As Paul stated, other tube companies know the bias needs of the amps so you can get other brands of tubes that will work. I just feel uneasy about putting tubes in without checking the bias. I bought some JJ tubes and plan to check the idle current when I install the tubes. Just waiting for my new Fluke to arrive.

Maybe I'm a tweaker, but I'd really like to install the pot so I can adjust the bias.
 
#14
gmahoog said:
Do you mean adjust the tubes for the best sound as you make the adjustment within a specified range, or are you talking about a recommended bias from the tube manufacturer?
Click to expand...

No, I'm talking about setting the current through the tubes to its optimum value. Too cold (bias voltage set too high) and the amp will sound sterile. Too hot (bias voltage set too low) the amp will sound warm but the tube will fail faster.

Paul
 
#16
I think I understand know, thank you Paul! But what to do when one of power tubes fails? I suppose it's constant headache?
I haven't also found information how the matched pairs are arranged. I know that matched sextet is the most safe way to go, but I'm still curious.

The Buster I'm looking at has got new Sovtek 6L6/5881WXT installed. I know that it is not direct replacement for a 6L6GC but it sounds good (I know that TBer "scotch" is using them in his Buster).
 
#18
jetofuj said:
I think I understand know, thank you Paul! But what to do when one of power tubes fails? I suppose it's constant headache?
I haven't also found information how the matched pairs are arranged. I know that matched sextet is the most safe way to go, but I'm still curious.

The Buster I'm looking at has got new Sovtek 6L6/5881WXT installed. I know that it is not direct replacement for a 6L6GC but it sounds good (I know that TBer "scotch" is using them in his Buster).
Click to expand...

The 5881 is also called 6L6WGB. It's a rugged version of the 6L6GB. It has less plate dissipation and voltage handling than the 6L6GC. It will therefore give less output in a circuit designed for the GC version. Good for guitar players as it saturates at an earlier point but for bass we need all the power we can get.

Paul
 

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