Fender Rhodes Electric Piano Amp Refurbishment

A Southeast Texas area church had a wonderful Rhodes Piano that needed some attention.  Whenever the unit was powered on, a loud hum was all that came through the speakers.  Time for the UnbrokenString Crew to go to work!

The Fender Rhodes Piano consists of a keyboard section, containing keys, action, and tuned rods that work in the same manner as tuning forks. The rods vibrate when struck, and the motion is sensed by a coil not unlike a guitar pickup. From there, the signal is sent to the other section, a powered stereo loudspeaker assembly seen here.


The speaker cabinet is two-faced e.g. loudspeakers fire from both the player’s side and the audience’s side.  A pair of loudspeakers are assigned to each output of a stereo amplifier.  The pairs of loudspeakers are across from each other in the cabinet, one firing forward and the other one back.  This enhances the swirly, phased sound of the instrument.


These loudspeakers are Fender branded CTS units.  The metal box in the background contains power and input circuitry.


CTS built these loudspeakers in June of 1975.


This part number indicates that these are 32 ohm AlNiCo loudspeakers.  This is a standard-issue Rhodes Piano unit.


This voice coil is totally cooked.  The motor drags badly in the magnet.


This voice coil is open-circuit but moves smoothly in the magnet.  Is a repair possible?


There is the broken voice coil wire.  This wire is really cooked, so we will elect to replace the loudspeaker with a pair of modern 8 ohm units wired in series, to yield the proper 16 ohm load to the amplifier.


We have removed the panel at the end of the cabinet.  The power transformer is visible to the right.  Each channel has a separate input here.  Also, a special cable from the Rhodes keyboard attaches here.


The power cord for this unit is no different than an extension cord.


Instead of a regular extension cord, we will use a SmartPower unit to power-up the unit and protect it from surges.  Think ‘mini-Furman unit.’  I also sell these, BTW.


These transistors read as short circuit.  I think we now know everything we need to know to make an intelligent quotation.


Name, rank, and serial number please.


One output of the power supply assembly is 25vdc for the keyboard section.


The keyboard voltage is set by a potentiometer accessible through this hole.


The power supply filter cap is in great shape for its age!


Likewise, these guys look great and test good.


Everything here is as it should be.


Steven removed one of the damaged loudspeakers.


Over the years, the gasket glued itself to the cabinet.


A little extra cleanup won’t hurt a thing.


The circuit board for the power amplifier is a hand-drawn affair, typical for the 1970s.


The board designer was nice enough to add is some text that would help the amp tech find his/her way around.


Some power resistors were burned up.  All of the components to the right of the transformer were replaced.  The transformer is for inter-stage coupling, not power.


Some power transistors were hand-selected for duty in this amplifier.


The repaired amplifiers are re-installed in the bottom of the cabinet.


We are ready for final test!


Amplifier design has certainly changed over the years.  This is a unique design that has withstood the test of time very well!  The customer was VERY pleased with the finished job.  Weather Report Cover Band, anyone?

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE

Peavey Citation MK IV Two Channel Guitar Amp Head Repair

Rod had this Peavey head kicking around and thought it was time to put it to good use. However, it didn’t work at all. Could the Unbrokenstring Crew work its magic and bring this road warrior back to life?
A quick scan of the front panel shows that the input circuit sports the sort of flexibility that the Peavey Marketing Department loves to explain to anyone who would listen…
Each channel has independent gain, and a master volume to Rule Them All.  Effects can be inserted via the front panel.
On the rear panel, we have parallel speaker jacks and the usual ground/no-ground power switching.  Peavey often married different front panels, which contained preamp circuitry, to different rear panels, which carried power and audio amplifier components.  The ‘series’ number goes with the power amp, not the front panel.  We Got This.
Name, rank, and serial number, please.
Pulling the front panel, we see that all of the components are mounted on one circuit board.
I took a few pictures to be sure that the wiring and cables were returned to the same spot when we are through.
The cable to the right is just wired to the power indicator.  The other two carry signals.
This is a better view (to be sure that they cables are properly oriented on their pins.
The front panel is free of the rest of the unit.
All of the controls and switches will be cleaned so this assembly comes completely apart.
We can now clean and lubricate everything now.


Can you spot the broken solder joints?
Someone has been here before!  This needs to be cleaned up, too.
The Blue Shower is a good cleaner.  The DeoxIt contains a lubricant for the potentiometers.  Good Stuff!
Back Together it all goes!
This screw hole was stripped out.  First, we will soak the stripped hole in the wood with this wood hardener.
Next, a birch dowel is cut to partially fill the hole.  The dowel reduces the apparent diameter, allowing the screw to hold.
With the stripped hole repaired, we are back in business!
This unit plays very well, and all the controls and switches are Like New!


Thanks for reading all the way to the end!

CONTACT – David Latchaw EE