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Zero Cool 15th January 2005 02:18 AM

Help with some SWR Schematics
I picked up a SWR workingmans 300 bass amp that is in need of repair. I found some shoddy repair work had been done previously and the mica insulator for the BIAS transistor had slipped down letting the case of the TO-220 device contact the heatsink. I am assuming this is what blew up 3 of the 4 Sanken 2SC3264 output devices. (all N-ch amp)

SWR was kind enough to send me the schematics. But, the schematics are for a REV D board and i have a REV A board. No big deal, almost everything is the same, except for a few things. there are 2 resistors that are swapped and 3 resistors missing on my board.
SO, im wondering WHY the change and if i should implement the changes to my board.

There are no markings on my schematics indicating copyright, but i assume so. your thoughts on posting the schematic???

I would be glad to email the schematics to whom ever would like to take a peek and help me sort out the Revised items in the mean time.



BobEllis 15th January 2005 04:56 AM

Working too late at night I forgot the insulator on my A75's bias transistor. The inputs blew after a few minutes of trying to get the offset under a couple volts. You might want to do at least a cursory check of all semis.

Shoot me a copy of the schematic. If you can annotate the changes since rev A, it would be helpful.

Zero Cool 15th January 2005 05:41 AM

Email sent.


Enzo 15th January 2005 08:16 AM

Make sure to get REAL Sanken 3264s, there are planty of fakes. MCM has been selling good ones, and I know there are som eother resources. But there are scads of bogus ones that cannot come even close to real 3264 specs.

My shop was an authorized SWR warranty facility, but now SWR is part of Fender. Fortunately I am also a Fender authorized station. SOme of the documentation of SWR lines is spotty. Good OEMs add notes for each revision, SWR tended not to.

What drawing number do you have? SWR liked to draw schemos "this circuit used in all models after serial numberxxxx." And then add notes like such and such model used only two output devices and so on.

I would not invoke the changes until you know what they were for. Resistors may have changed because they went to a different transistor for some function. Install the old type xstr with the new resistor config and you have trouble. SOme changes might be nothing more than a series RC swapping places. SOme changes might be for convenience of manufacture.

SOme changes were made to accommodate the use of one board in several models. Changes may be irrelevant to one application but matter to the next. In the sense of GM making trailer light wiring standard on later car models. WOuld make little point for you to update your car's wiring like that unless you planned to tow a trailer.

Make REAL sure the speaker connections, cable, and cab are OK. ANd make sure no shorts to ground are on the speaker out buss. These amps are not graceful in the presence of load trouble. I don't want your repair to blow itself back up instantly.

These amps are the classic case where a Variac is reeeeeal handy.

I will consult the archive disc to see if I have diferent drawing numbers than yours.

Fender makes many schemos available on their Mr. Gearhead web site. I don't know if they have aded the SWR documents there or not.

Zero Cool 15th January 2005 03:18 PM


Thanks for the help, I tried to send you an email throught he board but it wont let me. if you email me at i will email you the schematics i have and what is different.

My Board is a 170010A board and the scematics only list a 170010D


Zero Cool 16th January 2005 04:15 PM

Still need your email Enzo! :bigeyes:


Peat 7th May 2012 12:19 PM


I also am interested in SWR schematics.
I would be glad if someone would send some.



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