How to rebias an amp

[Reg]

Apologies if this has already been covered but I wondered if anyone knew of a website that explains in really SIMPLE tems, how to go about rebiasing an amp?
I have a Koch Twintone II that runs on 2EL34s and the manufatcturers warn of death, disease and destruction to anyone either not using their valves (tubes) or trying to do it without the aid of a tech who would no doubt charge a large amount of money.
Thanks very much

 

[HipKitty]

I suggest you read Randall Aiken's stuff as a starting point here:

www.aikenamps.com

Go to the Tech section. This will get you started in understanding what bias is and the difference between fixed and cathode biasing.

Then go to:

www.duncanamps.com/technical/lvbias.html

What can scare off most non-techies is the math......

There are plenty of resources available for those interested.

The word of caution:

There are dangerous voltages within your amp. If you do not know what the components in your amp are, I'd suggest that you do not attempt anything...the voltages inside are lethal! :shock:

THEY WILL KILL YOU!

 

[Reg]

Thanks very much for the links.
Way too technical for me. I like (need) articles with lots of brightly coloured pictures!!!!
The potential for death is obviously a factor that I would have to take into account (don't want my ex-wife getting her hands on my meagre savings just yet!)
I'll just have to find a local tech and hope I don't get ripped off

 

[fitz8005]

go to www.eurotubes.com and check out the menu, there's a few videos that explain pretty simply how to rebias.

 

[Reg]

Thanks very much.
Now I like video. Much easier to understand!

 

[kentran]

go to http://www.eurotubes.com and check out the menu, there's a few videos that explain pretty simply how to rebias.

Thanks for your sharing! I appreciate this.

 

[darkbluemurder]

Bias in tube amps is necessary for safe operation of the output tubes. Generally this means that the grid must be at a lower voltage than the cathode.

In amps with grid bias (often referred to as "fixed bias"), the cathodes are at ground (= 0V) and a negative voltage is applied to the grids of the power tubes. "Biasing" means adjusting the negative voltage so that the idle current of the tube is in the safe zone of operation. Since different tubes draw different amounts of current the negative voltage may have to be adjusted upwards or downwards. Some amps have a trimpot inside to do that adjustment. Mesa Boogie amps usually do not have the pot to adjust, so you have to either use different tubes or change a resistor in the bias circuit to adjust. Keep in mind that this is not a user serviceable adjustment unless you know what you are doing.

Cheers Stephan