MC2505 amp with shorted outputs needs help

[david winter]

Hi,

I'm trying to repair a MC2505 amplifier which has both channel shorted. The serial is in the 59K range.
This amplifier has been recaped in early 2015 and was wired in 220V.
Three of the four 32-070 (2N5303) output transistors are shorted between collector/emitter.
I didn' test the Q17/Q18/Q19/Q20 (023 / 024) drivers as I need to remove them but my ohmeter doesn't show any short.
However, the damage went a little bit further than just the outputs: both Q13/Q14 are also shorted (one C/E, the other C/B), one diode went resistive and several resistors increased in value.

In other words, I want to make a quality repair by replacing all semiconductors on both output boards.
Which brings the obvious question: is there a list of equivalent semis for the MC2505 ?
If not, anybody found exact or very close subs which work well ?

Thanks,

David

 

[cduarte]

here's the mcintosh transistor sub bible... http://www.tubebooks.org/file_downloads/McIntosh/semiconductor_data.pdf

 

[c_dk]

As a historical document the 1975 list is interesting but since almost all the subs have been discontinued decades ago it is pretty worthless as a sub source.

The 1984 and 1990 semi data sheets are much better but they also are now mostly obsolete also.

Three of the four outputs failed? Sounds to me you have some deep seated issues that will demand a qualified tech's attention.

There have been past posts on using modern TO220 case devices as subs for the obsolete TO66 devices. I have found some oscillation issues with some of the much faster modern drivers, other posters not, your results may vary.

My test bed MC2505 is awaiting me getting caught back up after my recent health issues.....

I have tried on numerous occasions to provide TO-92 case subs, within the last month Phil's MA6100 for example........if you are not going to use and reference the AK internal search engine........