Re: Rock ola 474 amp

On 8/10/20 12:37, Dave N. wrote:
> I just pick up two Rockola 474's and the one I'm working on has static
> in the right speaker all the time sometimes you can hear it over the
> music. I have replaced most all of the electrolytic capacitors on the
> driver board, the pre amp and the power board with no change in the
> noise. has any one ever had this before.

If you have an oscilloscope you can probe the same points on both 
channels looking for the noise.

Otherwise you can narrow it down, does the volume of the static vary 
with the volume control or is it always at the same volume? Does it go 
away during scan when the box is muted?

It's most likely a transistor. Without test equipment you can often 
narrow it down by temperature. Most noisy components are noisier when 
warm. Get a can of freeze spray (or computer duster, just turn it 
upside-down) and give a light spray to each transistor during operation. 
The one that causes the noise to go away or drop substantially is the 
culprit.