Bias Check As Preventive Maintenance?

[anatech]

Hi darkfenriz,
There is a correlation there, but it isn't accurate at all. You should really be measuring the current.

-Chris

 

[AcidJazz]

Hi AcidJazz,
The bias checking / setting procedure for Adcom involves running th e amp until the heatsinks are hot and then letting it cool. Then you check.

I'll bet your bias is high now. As a warranty service tech I did set the bias current on the low side of normal, but within range. Even with a lower bias, your distortion and sound quality shouldn't change on these unless the output transistors are not matched properly.

-Chris

Mhnnn...I have never been able to run my 535 'til it gets hot, warm yes but never hot..have seen the clipping indicator lights come on a couple times many years ago. I ran the amp for a couple hours before checking the bias and it read about 2.4mV, the heatsinks were barely warm.
I may have to use a dummy load to get the heatsinks hot. I will open it up and check again.
My amp has never needed service in 20 years.

 

[anatech]

Hi AcidJazz,

I may have to use a dummy load to get the heatsinks hot.

Yup. You run around 1/3 power with a 1 KHz sine wave for abou 20 min. The heatsinks will be hot then. Let it cool down until the bias is not changing much anymore (disconnect load, signal to zero). Measure the current then.

-Chris