Author Topic: Rhodes Mk1 Stuitcase - Peterson Preamp & Amp Repair  (Read 272 times)

Offline frenchji

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Rhodes Mk1 Stuitcase - Peterson Preamp & Amp Repair
« on: March 30, 2021, 12:51:55 PM »
I recently acquired a '75 Rhodes Mk1 Suitcase model and I couldn't be more ecstatic!  I've always wanted a Rhodes and found one that was semi-affordable, knowing that I would have to repair some elements.  I don't need or plan on restoring to exact era specs but I want to at least pay "homage" to the original design.

I'll start with the pros:

Directly from the harp this Rhodes is dead quiet and sounds exactly like how I imaged a Rhodes should!  There seems to be no pickup issues and besides one sticky key, plays nicely.  I might replace the grommets but I won't need to replace any bushings for the time being, although, I suspect that would be beneficial.

Now for the cons:

No Tremolo!  When Tremolo is engaged (or disengaged as well) the bulbs don't appear to light up.  Might be as simple as replacing the bulbs?

One of the notes barely has any sustain.  The tine and tone bar look fine.  This is why I might replace all the grommets as mentioned above.

Only one side of the speakers work and you can tell in the pictures that one of the amps needs some work.  There is a very obvious blown resistor on one of the amps which I'm assuming was caused by a temperamental/faulty germanium transistor?  The amp is very noisy but I'm assuming a large part of this is the faulty power amp.   

There is quite a bit of corrosion in the cab portion of this piano, as you can see in the pictures.  Miraculously, the speakers appear to be functioning though. 

Now for some questions:

Should I attempt to repair the power amps or should I buy a brand new set from the few people who make replacements?  I'm fairly confident in soldering so I'm open to DIY if possible, is this something I consider attempting on my own?  Doing a simple re-cap job I'm confident I can do just fine, replacing the germanium transistors with silicon might be something else though.  If I do buy replacement amps, which ones should I consider?

What is the best way to test the speakers to make sure they are fully operational?  I obviously can't test with the amps since one is broken and the other looks like it took a swim.
« Last Edit: March 30, 2021, 12:53:36 PM by frenchji »

Offline Will

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Re: Rhodes Mk1 Stuitcase - Peterson Preamp & Amp Repair
« Reply #1 on: April 09, 2021, 12:28:29 PM »
Hello Frenchji,
I am not the most experienced user here but here are my tips.

Quote from: Frenchji
Only one side of the speakers works [...] What is the best way to test the speakers to make sure they are fully operational? 
I usually use a 9V battery and connect it briefly to the poles of the loudspeaker. You can also connect it to the tip and sleeve of the jack connected to the speakers. You should hear a "pop" and see the membrane moving forward (or backward if reverse connection). This is very basic testing of course.

Quote from: Frenchji
...the amps needs some work.  There is a very obvious blown resistor ...
Your amp needs some electronics diagnostics to understand why the resistor has burnt. Replacing failed components would keep the circuit close to original and shouldn't be too costly.

Quote from: Frenchji
No Tremolo!  When Tremolo is engaged...
Same here. Some diagnostics are needed to find out what the problem is.
Here are two topics to start. Be aware that my Rhodes has Janus preamp (without bulb)
https://ep-forum.com/smf/index.php?topic=10265.msg57985#msg57985
https://ep-forum.com/smf/index.php?topic=10290.msg58076#msg58076

Last, your amp, preamp and power supply need to be recaped indeed. Electrolytic caps do not age well. You can find rebuild kits on specialized suppliers online shops which are well documented and inspiring. Here is a topic about my preamp upgrade :
https://ep-forum.com/smf/index.php?topic=10294.0







« Last Edit: April 11, 2021, 01:13:46 AM by Will »

Offline frenchji

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Re: Rhodes Mk1 Stuitcase - Peterson Preamp & Amp Repair
« Reply #2 on: April 09, 2021, 02:54:19 PM »
Hello Frenchji,
I am not the most experienced user here but here are my tips.

Quote from: Frenchji
Only one side of the speakers works [...] What is the best way to test the speakers to make sure they are fully operational? 
I usually use a 9V battery and connect it briefly to the poles of the loudspeaker. You can also connect it the the tip and sleeve of the jack connected to the speakers. You should hear a "pop" and see the membrane moving forward (or backward if reverse connection). This is very basic testing of course.

Quote from: Frenchji
...the amps needs some work.  There is a very obvious blown resistor ...
Your amp needs some electronics diagnostics to understand why the resistor has burnt. Replacing failed components would keep the circuit close to original and shouldn't be too costly.

Quote from: Frenchji
No Tremolo!  When Tremolo is engaged...
Same here. Some diagnostics are needed to find out what the problem is.
Here are two topics to start. Be aware that my Rhodes has Janus preamp (without bulb)
https://ep-forum.com/smf/index.php?topic=10265.msg57985#msg57985
https://ep-forum.com/smf/index.php?topic=10290.msg58076#msg58076

Last, your amp, preamp and power supply need to be recaped indeed. Electrolytic caps do not age well. You can find rebuild kits on specialized suppliers online shops which are well documented and inspiring. Here is a topic about my preamp upgrade :
https://ep-forum.com/smf/index.php?topic=10294.0

Thank you for the insight!

I went ahead and sent in the electronics for repair as I'm a little out of my comfort zone there.