undo old repairs

[calman46]

I'll try this here , I want to put this amp board (2325) back to original . It seems its been rebuilt at one time with different parts . I don't like having different output transistors on the L&R and different power transistors also.All the original parts are available so I'm going for it

 

[calman46]

Ok I think I figured out the repairs . The driver transistors (H708, H709) have been changed to TIP41C, Tip42C (this might explain the added resistors ) and the outputs have been changed to 2SD424, 2SB554 and lastly H715 has been changed to a BD139. What I can tell in my limited knowledge is the replacements are actually better,they exceed all the basic operating specs. How do you figure out if a certain driver trans. will work with a certain output trans. This might be to complicated to explain here, I understand . I couldn't get one of the original outputs so I 'm going to leave them alone .

 

[Fred Longworth]

I would be concerned with bandwidth, especially as far as the driver and output transistors. Many techs don't pay attention to this factor. Using transistors with radically different bandwidths than the originals can lead to oscillations.

Other than that, I don't believe that the new transistors would sound much different. If I were looking to put something "back to stock," I'd look hardest as the preamp section.

Fred Longworth

 

[Jetcone]

HI Fred:
Where do you find the bandwidth specs for such out of date transistors. I know my original 2275 has Fairchild output transistors and have not found any lit on Fairchild.
My other 2275 has Motorola output transistors.
These units are so old now the literature is scarce.

Any tips would be appreciated.

jon

 

[rickr15]

http://www.datasheetarchive.com/

Lot of PDF files on the old semiconductors can be found here.

 

[vintagestereo]

I'll try this here , I want to put this amp board (2325) back to original . It seems its been rebuilt at one time with different parts . I don't like having different output transistors on the L&R and different power transistors also.All the original parts are available so I'm going for it

Sounds like an amateur job. I HATE it when people without the requisite knowledge or skill do this themselves. It just KILLS the value of the unit.

 

[Nakdoc]

Marantz themselves changed the OEM transistor suppliers a few times, and then ran out of replacement parts stock. The trick is to make sure drivers and outputs are complementary pairs. We're working now on a 2265 with badly mismatched ECG outputs, which failed, and will replace both drivers and outputs with true complementary trannies.