CARVIN Belair212 Manuale utente

- 1 -

How to bias:

Belair212, Nomad

Rev A

8/18/2009

carvinservice.com

- 2 -

Only a certified technician should bias Carvin amps, this is very

dangerous, you can get hurt, please be very careful when working

with any tube amp!

If you have changed the tubes make sure they are a matched set. When you bias the

amp at 75mA and the tubes are matched you will have the desirable 20mA going

through each of the 4 Power tubes.

- The Bias for the Belair212, Nomad should be 75mA at 120VAC.

STEP 1

These are the tools you will need:

1. A flat head screw driver

“small”.

2. A multi-meter, w/ milli amp

reading.

3. Banana to clip leads.

4. Amp stand (optional).

STEP 2

Take the amp out of the amp

enclosure (cabinet). Set it in an amp

stand. Be very careful with the tubes

they can break.

NOTE: If you don't have an amp

stand then support the chassis on

some blocks of wood so that the

power tubes are not touching

anything - they get very hot!

- 3 -

STEP 3

Plug in speaker to output 1 or 2, they

are both the same, both jacks are in

parallel.

NOTE: For speaker setup click on

“Troubleshooting” and “Speakers”.

IMPORTANT: Do NOT turn on the

amplifier without a speaker plugged

in!"

STEP 4

Make sure the OHM setting is

correct. Improper setting will result

in damage to the amp!

NOTE: On the back is where you

will find the OHM setting, make sure

the speaker matches the OHM

setting.

STEP 5

A) Lower the volume down on both

channels.

B) Unplug your guitar cord from the

input of the amp.

NOTE: If you have signal going

through the amp, it will not be the

true reading, when you set the bias.

- 4 -

STEP 6

A) Connect the leads to the meter. B) Set your meter to the milliamp (MA) position.

Make sure the fuse inside is good.

NOTE: If the Fuse inside your meter is open, the meter will never work. It will

always read 0mA. In the meter above, mA and COM is selected, you have the

option to plug in the lead on (A) but because the setting will be set to 75mA it is

best to use mA.

STEP 7

1. 2.

Connect clips from meter to Standby Switch. It’s easier to clip the leads to the

wires that go from the standby switch to the main circuit board as pictured.

IMPORTANT: Never power the amp ON before connecting the leads, you will

get a big spark, you may blow the fuse of the Meter and or damage the amp.

- 5 -

STEP 8

Plug in AC Cord.

NOTE: Sometimes when the AC Cord

is new it does not want to go in all the

way. Push firmly to force it in, if that is

the case.

STEP 9

Turn the Power Button ON. Wait 2

minutes for the amp to get hot, after the

2 minutes you should see the meter read

current. It will start slow then increase

up to 75mA, adjust it accordingly.

NOTE: Do Not turn ON the Standby

switch, leave it on STANDBY.

STEP 10

Check your meter at this point, if it goes

over 75mA, lower it by turning the bias

potentiometer with the screw driver,

clock wise, if it’s under 75mA bring it

up by turning the potentiometer the

other way.

- 6 -

It is OK and normal for the bias reading to fluctuate a little bit and may not be

exactly 75mA but as close as possible.

IMPORTANT: I was using a current shunt to measure the current that’s why the

pictures below shows mV, your meter should read (mA).

Good Bias High Bias Low Bias

STEP 11

Power down Steps:

1. Turn OFF the amp

2. Disconnect the meter leads.

3. Unplug your AC cord and wait for the tubes to cool down, so that you can put the

amp back in the cabinet.

IMPORTANT: During biasing and normal amp operation if there is a burning smell

or loud crackling noise that comes from the speaker, you should turn off the amp as

your may have a bad tube. The same is true if your meter reads higher that 150mA

or goes into overload. The tubes should never glow RED on the gray plate material,

the largest metal part inside the tube. This indicates a major problem and extremely

unsafe condition. If this happens turn off the amp immediately!

IMPORTANT: The tubes get very hot! Don’t touch them, you will burn your

skin if you do. If the amp is ON the tubes will get hot, even if you are not

playing the amp, wait 30 minutes before handling the unit to ensure the amp

cooled down.

IMPORTANT: This is not the only way to set the bias on this amp, this is the

Carvin Approved method which is used on the Production line in the San Diego,

California Factory.

- 7 -

NOTE: If the tubes are getting hot and 3 to 5 minutes went by and you don’t see

any reading on your meter check your meter, you may have the leads plugged into

the wrong place in your meter or the fuse of your meter is open.

EXPORT(230-240VAC 50Hz): Follow the same instructions.

Comments or questions email us at Carvinservice@carvin.com

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