Audio of Oregon CC-3 output transistor replacement

[mjarve]

I'm working on a the amp referenced in the title, and it has one bad output device, a Motorola 2N5630 (NPN, 120V/20A, 1MHz, 200W). The amp is apparently based off the earlier AoO CC-2, which was purportedly designed with these slow, but powerful output devices in mind.

Now comes the issue. It would seem that most of the recommended substitutes differ enough in specs (hfe, Vebo, etc) that I would almost have to replace all the output devices in the channel (and, by extension, the other channel) to ensure stability. The question is, is anyone here familiar enough with the CC-2 or CC-3 to recommend a course of action? Is there possibly a decent drop-in replacement, or am I going to have to modify other parts of the circuit to make it work; or is there some merit to trying to scavenge another 2N5630 from another amp (I understand they were used in some Peavey PA amps as well)?

Any guidance would be appreciated.

 

[Ian Finch]

Have you checked out this thread, which at least gives us pics and some necessary details?:
http://www.diyaudio.com/forums/solid-state/218597-audionics-oregon-cc3-power-amp.html. With no schematic or manufacturer details on the web, it will need your input to describe the important features, as needed.
It appears to be a simple output stage with maybe only 2 output transistor pairs per channel? If so, matching transistors shouldn't be a big issue.

 

[mjarve]

Have you checked out this thread, which at least gives us pics and some necessary details: http://www.diyaudio.com/forums/solid-state/218597-audionics-oregon-cc3-power-amp.html
It appears to be simple output stage with maybe only 2 output transistor pairs per channel? If so, matching transistors shouldn't be a big issue.

Yep, I checked that out. The only thing I'm really concerned about is that, reading up on the CC-2, it seemed there may have been some mojo going on to achieve a high slew rate and stability with reactive loads that called for more careful consideration.

I'd practically give a kidney for a proper service manual for this thing. Very nice sounding amp (when it's not blown up), and I'd hate to screw that up.

 

[TerryO]

Yep, I checked that out. The only thing I'm really concerned about is that, reading up on the CC-2, it seemed there may have been some mojo going on to achieve a high slew rate and stability with reactive loads that called for more careful consideration.

I'd practically give a kidney for a proper service manual for this thing. Very nice sounding amp (when it's not blown up), and I'd hate to screw that up.

I don't know about a Kidney, but I sure would like to see a service manual and/or schematic for the amplier.

Best Regards,
TerryO

 

[Ian Finch]

....it seemed there may have been some mojo going on to achieve a high slew rate and stability with reactive loads that called for more careful consideration... .

With an Ft of 1MHz, 2N5630 would be vying for a place in the world's slowest slew rate audio amplifier stakes.

You haven't told us what the complementary pair transistor was, or whether its a quasi-complementary design or how many output transistor pairs but I'd be surprised if On-semi's audio transistors MJ15003/4 didn't do a better job all round. They aren't expensive and Ft is 2MHz - no big deal, so I don't think you will have anything to lose there as long as you replace all those in parallel, if they indeed are.

 

[mjarve]

With an Ft of 1MHz, 2N5630 would be vying for a place in the world's slowest slew rate audio amplifier stakes.

You haven't told us what the complementary pair transistor was, or whether its a quasi-complementary design or how many output transistor pairs but I'd be surprised if On-semi's audio transistors MJ15003/4 didn't do a better job all round. They aren't expensive and Ft is 2MHz - no big deal, so I don't think you will have anything to lose there as long as you replace all those in parallel, if they indeed are.

Should have qualified that with relatively high slew rate (36V/uS), which is quite a bit faster than the some others using the same unit (i.e. Dynaco Stereo 400 @ 8V/uS).

The outputs are complementary, with the PNP being the 2N6030.

I've attached the schematic for the CC-2, though, as I mentioned, the CC-3 seems to have a little more going on, at least on the front-end.

I'll give those ONsemi's a try. Just hope I don't end up with oscillation or worse.

I'll

 

[Ian Finch]

Thanks for posting that CC-2 schematic. It explains a couple of important features, like the use of current limiters MPSA 8099/8599ing to protect the outputs - but didn't.
I would double check (remove and properly test) some of those small transistors in the CC3, even if the amp otherwise appears to work.

I can imagine that front end having thermal stability and a couple more minor issues, so a revision would have been likely, if that's the only significant difference. These days, you wouldn't build a 100W/8R amplifier with those type parts, as most are obsolete and it could be done simpler and cheaper with more appropriate rated ones.

Still, sound quality is bound up in distortion, often intrinsic to old designs and as you fear, messing with old, less linear parts can spoil the fun by killing the nice distortion and possibly introducing instability and its not-so-nice distortion.

Any way you look at it though, your replacements need a Vceo of 100V minimum and finding complementary TO3 pairs will be difficult as you'll probably be tracking down NOS parts. Central Semi though, seem to still market the closely related types 2N5629/6029 which should be directly comparable. I have no idea of cost and availability, however. Considering the many designs here, using 2N3055 (60V parts) designs with 40V rails, I wouldn't be too concerned running 2N5629 with 45V rails.
http://www.datasheetcatalog.com/datasheets_pdf/2/N/5/6/2N5629.shtml