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Fender Rhodes 1967 - Student Fishtail Model Schematics - Amp Distortion

Started by Tim Hodges, September 08, 2016, 03:39:17 AM

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Tim Hodges

Hi all,

I'm in the process of restoring one of the early student models with the white pinstripe down the base of the fishtail. I've got the power amp with a local amp tech and he's having difficulty finding the right schematic (the one on the Supersite is for a 1968 version which is apparently different)

The 1968 Schematic

Does anyone have the schematics for a 1967 model?



The amp model number is "KB 1273"





The problem with the amp is that there is some noticeable crossover distortion, he's replaced the CC resistors which have drifted out of range and the ruptured electrolytic caps but it still persists. My suggestion is that both of those TO-3 transistors need to be replaced with matched pairs as I'm guessing this design is susceptible to it.
After doing a bit of searching around one of the transistors is a Motorola SJ6357 (TO-3), it's a Peavey part number assigned to the more commonly known MJ15003. So I'm hoping that if he matches a pair of MJ15003's the problem should be fixed.



Thanks

Tim






Bristol Electric Piano
UK

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Tim Hodges

Bristol Electric Piano
UK

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Tim Hodges

In the end I managed to find a pair of NOS Germanium transistors which had been matched for a Peterson power supply in my old stock box. These were then used to replace the old RCA Germanium and the mismatched Motorola Silicone transistor. These work perfectly and have reduced the crossover distortion significantly.

The tech also found that some of the transformer leads had worn down the insulation and were short circuiting. They had been in a position where it hadn't been a problem for some years but as soon as the board was opened up and the wires moved it kept blowing fuses. That has now been fixed but worth keeping an eye out for anyone checking over their amps.
Bristol Electric Piano
UK

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Cormac Long

[ADMIN MOD]

Moved post from Mike Borish to here.. (forum rules, keep sales pitches to for-sale section)
http://ep-forum.com/smf/index.php?topic=9280.0
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