Off Topic Rebias an amp

[koogie2k]

OK....A buddy of mine went and got a new amp. He gave me his old Crate Blue Voodoo 120 head and cab...(thanks bro ).

Now, this amp has stupid amounts of volume and the dirty channel is way out of control. I have read about this amp and switching out the tubes really reigns this thing in and I need to get some control over it. It is not the best amp in the world but it came in at a great price for me....FREE.

I read also that when you switch to different types of tubes...you have to rebias the amp.

How is this done? Beej....or anyone else? I don't play guitar in my band so this is not going on stage anytime soon...lol....

 

[candid_x]

Hey Koogs,

I think the Blue Voodoo is a fixed bias, like the Mesa. Just make sure the tubes you replace with are matched. No biasing required.

Changing out power tubes to another brand can make a huge difference, but it's also debated as to which is best. Same goes for Preamp tubes.

Here's a couple links you may find interesting.
Voodoo Amps Blue Voodoo 120 Mods, Modifications, Upgrades

http://www.dougstubes.com


I get most of my tubes from Doug, never had any problem. He tests everything before sending, and can give you recommendations.

For new (non-NOS) tubes I've had great satisfaction with the JJ Telsa over many others I've tried, in 6L6, EL34 power tubes and 12AX7 preamp tubes. I actually prefer Sovtek EL84's over JJ's, though.

Good luck and congrats on the cool score.

Bruce

 

[Adwex]

Not all tube types are compatible. For instance, to switch from EL34 to 6L6, a small mod is required.

When you replace the power tubes with the same type, the bias should be adjusted (or at least checked to see if its in spec). Usually, it's not a terribly difficult procedure, provided you know what to do, and have the proper equipment.

It should be noted that there are high voltages that can kill you in a tube amp. The rule of thumb when working on a tube amp is to always keep one hand in your pocket. NEVER poke around a tube amp with both hands. If one hand touches a high voltage point, and the other hand is grounded on the chassis, the high voltage jolt will go through your chest.......through your heart. Not good.

Preamp tubes do not require re-biasing.

Here are some good "how to" videos:
euro-q

Adam

 

[beej]

Hey Koogs-

It depends on the amp, really. I just poked around to see about that amp. Looks like it's self biasing so that's not something you have to worry about. (If you see bias points at the back of the amp then I am out to lunch though ...) Also looks like you can swap 6L6s or 5881s in the output section.

Worst offenders for sound will be the preamp tubes, from first to last. Swapping in different tubes & brands of 12AX7s can make a big difference. If it's too gainy for you (even with the gain turned down) you can always swap something else in the same family there (a 12AT7, etc.) If you don't play it loud you may or may not notice a change in the output tubes. Worth doing if they haven't been changed in a long time and have had lots of use. But again, doesn't look like you need to rebias them so you'd be ok. Just get in there and swap.

Also- if it doesn't have a 1/2 power switch, you can tame the volume by pulling 2 of the 4 output tubes (cuts the wattage in half). Usually the inside or outside pair. Note when you do this your speaker outputs double in impedance- the 4 ohm output becomes 8 ohms, the 8 becomes 16.

Free amp- solid!

Edit: damn, late to the game.

 

[koogie2k]

Candid...thanks for the link....I might just go that route....if re-tubing doesn't get it for me.

Adwex...yeah...I know it is a danger poking around in there....thanks.

Beej...yeah, the site Candid posted said in the first mod, they actually make the amp bias adjustable. So, I am with you on this. I will see what tubes this thing has and hit you with a PM for some suggestions. But, I won't get to that tonight. Thanks bro!

 

[TNT]

Koog,

I think that can be a killer amp - it's worht putting a little time and money into!!!! Those early Crate BV's had a great punchy tone!

What year is that one??