Let's just say I'm a stingy scrooge

[DesertRose]

Amps arrived at my place, one Marshall fitted with 6L6 and another had volumes going soft and loud.

Some say, the volume problem needs a replacement of a SET of new power tubes and some say the circuitry needs some adjustment whatever, blah blah
If I were to change to a new set of tubes, there is a need to re-bias again and things like that.
My local tech makes life difficult if I were to take it and let them do it cuz they will charge me at a RANSOM

So, i looked up on the internet and I had problems understanding the jargons on "How to bias an amp"
Anyone could tell me in LAYMAN terms ?
Thanks for everything

 

[Gearjoneser]

Re: Let's just say I'm a stingy scrooge

On Ebay, you can usually find someone selling a Bias Tool for about $20.
When this socket is put between the amp and tube, it'll give you a mA reading on a volt/ohm meter. First, make sure you're using the right kind of tubes for the amp......did that Marshall come with 6L6's, or did it come with EL-34?

If you have the chassis out, set some books under the trannies, so the electronics are exposed with everything hooked up. With a plastic handled miniscrewdriver, gently adjust the trimpot so that 6L6's read around 32mA and EL-34's read around 36-38mA. I usually set it to a number, strum the guitar for awhile, move up a number, strum, move up a number strum, just so I know which number sounded the loudest, tightest, boldest. Just make sure to keep the bias around those numbers, so you don't turn the plates red and fry the tubes. And most importantly, be careful when poking inside a live amp with a screwdriver. It's best to use one with a plastic handle, and don't touch anything else at the same time.

 

[Gearjoneser]

Re: Let's just say I'm a stingy scrooge

I've also biased amps without a bias tool, and did it totally by ear.
In that case, I dim the lights a little, so I can see if the plates turn the slightest bit red. If that happens, STOP, turn off the amp and let it cool for half an hour.
Simply adjust the bias pot while everything is plugged up. Sometimes, I lay the guitar on the floor and strum it, then tweak the bias pot so the guitar chord sounds it's best. You just want the amp to sound as good as it can without being weak or too pushed sounding.

This is the most "layman" way of doing it.

 

[kmcguitars]

Re: Let's just say I'm a stingy scrooge

Here's a pic of my Bias screw driver. Notice it has a plastic handle and it's wrapped up with electrical tape. The other screw driver crossed out as mentioned by Gearjoner should NEVER ! Be used inside a live amp.

 

[DesertRose]

Re: Let's just say I'm a stingy scrooge

Thanks guys

all these should help.
To Gear Ho:
The Marshall comes with 6L6 tubes and not EL34s.
I'm having the intention to change it back to 5881s since it originally came with that. So I was having the idea of re-biasing it since I'm going to put back the original tubes inside. I read somewhere that whenever the power tubes are being changed, they gotta be re-bias just like a carburetor. You change the air filters, you need to fine tune it again

So, its just like that.
Thanks guys