Noisy Controls in an SWR Red Head Bass Combo

This combo amp really turns heads whenever it is played.  However, over the decades, the controls have become noisy. Time for the Unbrokenstring Crew to do some remedial magic and get this unit back in top form!

This unit has a 1U rack space under the head unit, which is a nice touch!


Let’s take a look around the inside of the unit. The power transformer and heat sink dominate the center of the unit.


The preamp is hybrid solid state / hollow state.


Looking at the rear of the front panel, we see the input jacks and equalization controls directly mounted and hand-wired to the circuit boards.  Most of the work we need to do today is right here.


The configuration switches are seen here.  That big black block in the middle is the top of the heat sink.


We see the fan here, which blows the length of the heat sink.  The power transformer has a bit of tape and foam on it.


Looking at the inside of the rear panel, we see the power jacks and fuses.  Can you see the bridge rectifier?


This big potentiometer dominates the rear panel, setting the line out level.


From this angle, we can see a the filter capacitors.  Electrically, this unit is very solid.


Each control is rinsed out with some Blue Shower cleaner.  The cleaner is applied from the rear of the potentiometer, rinsing the crud away from the resistive element.


Then the control is dried with some compressed air in a can.


This anti-corrosive cleaner/lubricant works well on the actual resistive element and wiper.


This synthetic lubricant is just the ticket for lubricating the shaft.


After reassembly, the unit is checked out.  Note the ease by which the loudspeakers are connected to the head unit.


This unit is now fully functional, with no more control noise.  Back together it goes!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE