BGW 250D output transistors

[emazur]

Hi,

 

I got a BGW 250D that sounds very nice. While doing a recap I noticed that the complimentary output transistors on both channels are of different makers: the PNP set are Motorola SJ9216 and the NPN are RCA 6803515 (or GB03515). I know about the Motorola 9216 but can't find anything on the RCA.

 

 

The manual says they should be MJ15016 and MJ15015. The solder behind is pristine and matches everything else, so I think this came from the factory like that. I know they probably have the same parameters, but the question is: does it change the sound in anyway?

 

Thanks.

Elias

 

 

[agedhorse]

Nope, those are house numbers for the same part or the factory equiv. Won't matter one bit.

[Shaster]

I'm probably repeating myself, but my first "real" PA had a BGW 250 for lows and mids, and a one space BGW for tops. Three way system with an unknown (can't remember) crossover. That was the late seventies when the 4560's were like the buffalo in the wild west; very plentiful.

 

I see they're still selling those amps used, but as this post suggests they'll likely need some TLC. Now if I just had the Senn 441 we used on our singer - that would be cool.

[agedhorse]

I just sold the last 441 about a month ago... dead mint condition. Went to a studio guy for a specific project.

[emazur]

Nope' date=' those are house numbers for the same part or the factory equiv. Won't matter one bit.[/quote']

 

Thanks agedhorse. I suspected it wouldn't matter. Since in a full complementary setup NPNs and PNPs don't really truly match and it's up to the circuit to compensate, as long as the parameters are similar, different manufacturers don't really make much of a difference.

 

I have a few quasi-complementary amps (AB model 200 and Soundcraftsmen MA-5002) which do sound a bit different that the fully amps I got. What's your take on the two topologies? I find the quasi a bit smoother, but less detailed.

 

Thanks.

Elias

[agedhorse]

While quasi amps use the same output devices and the assumption is that symmetry might be better, it's often ignored that the necessary drive circuitry is much less symmetrical, adding a whole host of more significant problems with more serious artifacts, IMO. There is do much more involved with the overall topology, especially overload handling and recovery, that factors into amp performance. In general, in well designed amps, symmetrical topologies tend to fare better, but of course the devil's in the details.

[agedhorse]

I used to have some involvement with AB back in the day, the 200 is a good example of an amp whose topology has changed over the life cycle from qasi to (iirc) a form of differential symmetry... one if my favorite topologies and one that I have continued to use in class AB based products.

[emazur]

I actually have the model 2220 but it looks like it's the same as the model 200. It's a quasi topology. I compared the AB with the BGW closely and I can definitely tell the more laid back character of the AB. Again, it could be other things in the circuit such as the op-amp input of the BGW.

[agedhorse]

Most certainly the difference can be other parts of the circuit (or specifically defects in the design).

 

Looked at my latest doc. notes and even in 1991, the 200 was still quasi while the other models had migrated to full complimentary. Don't remember why/\.