Re-biasing when changing a head on a head/cab stack

[nusstu]

Hi Softies,

I'm pretty new to tube amps and I was just wondering if I changed the head on an original VOX AC30 head/cab stack to a Fender Super Sonic head. Would that require re-biasing on the cabinet speaker since the tubes are different?

Thanks.

 

[Indigo_blues]

hiya,

I don't think so if you are just changing speakers...

the only time you need to re-bias is if you change your tubes.

 

[nusstu]

Hi,

thanks for the reply but I'm changing the head not the speaker cabinet. If I change the head from a 30W to a 4W, would I need a re-biasing or can I just plug in the 4W head?

Thanks.

 

[dodgethis]

I highly suggest you go read up on the net more, because if you can say a speaker cabinet needs rebiasing, you're getting your facts wrong.

 

[garbagetruckdriver]

are you confusing biasing tubes with selecting the correct speaker cab impedance?

Biasing is the act of adjusting the idle voltage on the grid of the power tubes. You only do this if you are changing power tubes. Usually if you are replacing tubes with the same type, you don't need to do anything. Replacing 6L6s with EL34 is definitely a cause for adjustment.

But it sounds like you are going to plug a fender head into your VOX speaker cabinet... Is that correct? If so, check what the impedance of that VOX cab is (4, 8 or 16 ohm) and make sure you plug it into the corresponding speaker output of the Fender amp head. You don't have to touch the tube bias for this.

 

[nusstu]

Hi all,

thanks for your reply, yup as you can see i'm a really new to this. Ok, so I need to check my impedance before I connect a new amp head.

Any other things to look out for before plugging it in, just afraid I'll fry my speaker cab?

BTW, where's a good place to get tubes for replacement (I'm looking for the 12AX7, EL84, EF86 and the EZ81 rectifier)?

Thanks.

 

[garbagetruckdriver]

I have to say I am partial to Doug's Tubes (www.dougstubes.com). Send Doug an email explaining what the amp is, and give him an idea of what kind of music you like to play, what tonal changes/improvements you'd like. He can spec each tube for you and provide you with matched sets for the power tubes. His online ordering is easy enough, and they pack the tubes very well for shipping internationally.

If you want to learn about Tube Amps, head over to Myles Rose's site - he founded Groove Tubes which was later sold to Fender.
http://www.guitaramplifierblueprinting.com/

Hi all,

thanks for your reply, yup as you can see i'm a really new to this. Ok, so I need to check my impedance before I connect a new amp head.

Any other things to look out for before plugging it in, just afraid I'll fry my speaker cab?

BTW, where's a good place to get tubes for replacement (I'm looking for the 12AX7, EL84, EF86 and the EZ81 rectifier)?

Thanks.

 

[L3stat]

Also, never turn on your amp without having a speaker load connected.

 

[Indigo_blues]

Also, never turn on your amp without having a speaker load connected.

Yup I was going say exactly the same thing.. surest way to blow your output tranny is to play the amp without any speakers connected.

Always double check that your speaker cabinet is plugged into the head before turning it on.

 

[nusstu]

OK, thanks all for the advice. So before switching on my amp head i'll rem to check that it's connected to the cab.

BTW, where do you guys get your tubes from? garbagetruckdriver recommends a US retailer. Any local retailers for tubes?

Thanks.

 

[Indigo_blues]

can try Martin Audio at Burlington Sq