Fender Rhodes Peterson student model power supply (diagram #6803-5(?))

[MichaelNuzum]

Hi all-

firstly I'd like to say hello, this is my very first post. This forum has been a tremendous help in the past, I've enjoyed being a lurker, happy to now be an active participant.

Back to my request, I need to see if I can find any documentation regarding the Rhodes student model with Peterson amp, specifically the power supply section, but if anyone has a schematic for a model other then the ubiquitous first version/ figure 11-19, I'd love to take a look at the whole thing.

For background: I have a model #1573 Peterson amp from a 1969(?) Rhodes student model on the bench. I am looking at replacing some components due to age and unreliability. It currently has germanium transistors and I would like to swap them out for silicon. I have done the homework regarding the swap in the output section, and the need to change the 2.7 ohm resistors with 12 ohm to properly adjust the bias. It currently has two Delco 801522 transistors for outputs. It seems I should be able to use an mj15016g with the resistor swap and be okay for that part.

Problem is, there is a third transistor mounted on the rear of the chassis, Delco DTG-110B, not on a heatsink, just direct mounted to the outside of the back wall. It feeds back to a small circuit board mounted vertically inside the chassis. This board is the power supply for which I am seeking a schematic. I have found the one available schematic for the student model preamplifier and power amplifier (Rhodes service manual figure 11-19) but it doesn't include the power supply. It references a separate drawing #6803-5.

One helpful source told me to look at the power supply for the Peterson 80 watt version, and while quite similar, it just isn't quite the same. Or at least not enough for my limited skills to find it helpful. If anyone has any experience with, or knowledge of, these particular amps and related germanium to silicon swap, I would greatly appreciate any insight or information you'd be willing to share.

[vintagekiki]

If you compare the schematics for the Student Piano and Instructor Piano you can see that the schematics is similar.

http://www.fenderrhodes.com/pianos/student.html

... An instructor version of the piano was also available, with the only difference being the interface on the control unit ...

http://www.fenderrhodes.com/org/ch11/fig11-19.jpg
Student Piano (First Version - 1968)

http://www.fenderrhodes.com/org/ch11/fig11-20.jpg
Instructor Piano (First Version - 1968)

http://www.fenderrhodes.com/org/ch11/fig11-23.jpg
Schematic - Power Supply - Instructor Console

http://fenderrhodes.com/html/history/narrative.html

[MichaelNuzum]

Hi vintagekiki- thanks for the reply, but that isn't what I am looking for. As I mentioned, I have the student model, and the schematic does not include the power supply, which is what I need. I have looked at pretty much every schematic in the Rhodes manual looking for a similar one, and I am aware of the instructor piano. While the schematic for the amplifier circuit section is quite similar, the power supply, in order to accommodate the instructors talk/listen back/and switching systems, is significantly different. I have looked at the instructors schematic verses the student circuit board in front of me and they have few to little similarities. Enough difference that it really doesn't help me decode the power board on the student model.

I have done my homework and if there is a quick google link, or if it is contained in the rhodes super site/ service manual, I have already seen it. I need someone with some deeper knowledge and maybe some old scans that aren't commonly circulated. Anything short of that, I probably already have it and it isn't what I need.

Not to be ungrateful, I do appreciate you taking the time to respond, but I just want to emphasize I am not here to ask someone else to do a web search for me. I have done a lot of independent searching before coming and asking for help (so as not to waste others' time), and I have all the commonly available info, and unfortunately it isn't complete. Thanks again.

[Jazz P Bass]

Question: what is wrong with the power supply?

Here is the "regulator" circuit: http://www.fenderrhodes.com/org/ch11/fig11-10.jpg

[MichaelNuzum]

Hi Jazz P Bass- thanks. The power supply has a dead (full continuity both legs and case) germanium transistor, which took out another resistor and maybe a few other components.

That regulator circuit you linked is for the 80 watt model, and while quite similar, they are different enough in component count and value, that I can't really interpret the difference. I must admit I am not much of a tech here, more of a musician who is handy with a soldering iron, so my abilities to look at different circuits and suss out what is what is pretty minimal.

That being said, I do have the board in front of me and see while they are both Peterson amp designs, and do share quite a few characteristics, they don't quite match. Thanks though.

[Jazz P Bass]

So is the supply board that you are having difficulties with the 'regulator' board?

How about posting a pic?

Which transistor is shorted?
The one mounted to the chassis?

[vintagekiki]

From the post it is not possible to see which voltage is missing.
pwramp voltage (+/- 30V) or preamp voltage (+ 25V)

http://www.fenderrhodes.com/org/ch11/fig11-10.jpg
Regulator board (+ 25V) is for preamp.

http://www.fenderrhodes.com/org/ch11/fig11-9.jpg
Power Module; Check preamp power supply transistor 2N3591A

If there is a voltage (+ 30V) check the correctness pwramp by introducing test signal 1kHz to the Aux amplifier jack
http://www.fenderrhodes.com/org/ch11/fig11-19.jpg

[MichaelNuzum]

Hi JPB-

1- yes, I believe so

2- I will be doing that tonight or tomorrow on a different post. I actually have another thread going in the amp repair section regarding the details. I just put this post here as a specific request for documentation.

3- correct. Not one of the two output transistors mounted to a heat sink, but the lone one bolted directly to the chassis wall above the filter capacitors.

Thanks.

[MichaelNuzum]

Hi vintagekiki- yeah, I have all those schematics. If you look at the notes section on the second link you posted, you will see it says "for power supply see dwg #6805-3". That's the documentation I was hoping to find, it seems it is unfortunately unavailable.

I am also familiar with the first link. It is a Peterson design, but for a different model with different part counts and values. They are quite similar, but different enough that I can't make one relate to the other.

I have looked at all the schematics on the fender rhodes site. I don't have a ton of knowledge, but I can see when things don't quite match, and that site does not contain a good enough match to be of help.

I cannot check for voltages or inject a signal because the amp has had the power transistor fail and take out itself and a few other components. Hence my search for the specific document I mentioned above.

Thanks for your help.

[MichaelNuzum]

UPDATE- I have tried (without much success) to draw out the circuit looking at the board in front of me, and it is indeed very much like the 80 watt regulator some of you mentioned earlier. I owe some of you an apology for me not being able to see the similarities and denying that they were alike. I humbly apologize. That being said, they are still a few components different, so I still have some work to do figuring this out.

Thanks again for all your help, everybody.

[MarkusBass]

I think that in the other thread you have all the answers regarding the schematic. Please don't continue two threads because this is very confusing. In one thread you have answers from the other thread.

Mark