400A bias adjusting

[Mywing]

Hi all,
as recommended me by Nelson I would adjust the 400A bias, but I don't know how.
Could someone that has already done with success, suggest me the procedure to follow?
Thank you so much.

[Nelson Pass]

Each channel has a bias potentiometer which is used to set
the bias. The bias should be set so that after one hour operation,
with the cover on, each channel should run about 50 deg C. in
a 25 deg C. room. This means that a ordinary room temperature
the heat sinks should be at the temperature where you can put
your hand on them for about 10 seconds.

The critical thing is not to accidentally find yourself biased at too
high a current figure, otherwise you risk blowing the channel up.

You must monitor the current draw of the channel, best done
by reading the voltage across one of the .33 ohm emitter
resistors on the output stage. Since it takes time for the amp
to warm up and the bias is somewhat temperature dependent,
you want to adjust the value of the bias very slowly, and then
wait while monitoring the current draw.

If the channel is running cold, then you increase the bias above
the existing value by a little bit. Then you wait.

Did I mention that there are hazardous voltages and stuff
inside the amp? If you don't know to do this safely, then don't
try it - find a technician and buy him a 6 pack.

[Mywing]

Thaks boss. I'll try that.
A last question: where is exactly situated the bias potentiometer?
Cheers

[Mywing]

Hi guys,
I've noticed, after about 4 hours of work, that the handles and the front panel become very warm, at least how much the heatsinks.
Is it normal?
Cheers

[Zen Mod]

Originally posted by Mywing
Hi guys,
I've noticed, after about 4 hours of work, that the handles and the front panel become very warm, at least how much the heatsinks.
Is it normal?
Cheers

read again what you wrote ......


and tell me - are you really sure that you don't know answer ?

tip:

make that front plate and handles of wood .......... then they will be just slightly warm

[Zen Mod]

Originally posted by Mywing
Thaks boss. I'll try that.
A last question: where is exactly situated the bias potentiometer?
Cheers

gimme a good pic of pcb and I'll tell you

[Mywing]

Originally posted by Zen Mod



gimme a good pic of pcb and I'll tell you

I've already found them by myself.
Thanks anyway.

About the warmth of handles and front panel, it sounds strange to me that it is so high, I own other amps including a valvestate with eight 6550 and handless and panel remain cold.
Unfortunately, this is my first experience with a class A: sorry if I annoy you with silly questions, I will try to avoid them in future.
Greets,
Nino

[Zen Mod]

Originally posted by Mywing


I've already found them by myself.
Thanks anyway.

About the warmth of handles and front panel, it sounds strange to me that it is so high, I own other amps including a valvestate with eight 6550 and handless and panel remain cold.
Unfortunately, this is my first experience with a class A: sorry if I annoy you with silly questions, I will try to avoid them in future.
Greets,
Nino

number of smilies can tell you that I'm not annoyed .......

there is unlimited number of questions one can ask , under condition that he show doing own home work ;